ANSS/USArray National Backbone Network

FINAL REPORT Incorporated Research Institutions for Seismology Subaward Agreement No. 383 Under NSF Cooperative Agreement No. EAR-0004370

Station CCUT—Cooperative Broadband Seismograph Station Near Cedar City, Utah (ANSS/USArray National Backbone Network)

Prepared for Incorporated Research Institutions for Seismology Washington, D.C.

Prepared by Walter J. Arabasz, David L. Drobeck, Relu Burlacu, Kristine L. Pankow, and James C. Pechmann University of Utah Seismograph Stations Department of Geology and Geophysics University of Utah 135 South 1460 East, Rm 705 WBB Salt Lake City, Utah 84112

July 7, 2006

DISCLAIMER This document was prepared as an account of work to the Incorporated Research Institutions for Seismology (IRIS) and the National Science Foundation. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government, the National Science Foundation, IRIS, or the University of Utah. The views, opinions, and conclusions expressed herein are those of the authors and do not necessarily state or reflect those of the United States Government, the National Science Foundation, IRIS, or the University of Utah.

ii

TABLE OF CONTENTS

___________________________________________________________________________ Page EXECUTIVE SUMMARY

vi

ACKNOWLEDGMENTS

vii

1.0

INTRODUCTION 1.1 Background 1.2 Cooperative Funding of Station CCUT 1.3 Project Objectives 1.4 Project Timeline 1.5 Scope of this Report

1-1 1-1 1-1 1-2 1-2 1-2

2.0

SITE SELECTION 2.1 Background 2.2 Noise Testing, Autumn 2004 2.3 Location and Site Conditions of Station CCUT 2.4 Site-Use Permits

2-1 2-1 2-1 2-2 2-2

3.0

INSTRUMENTATION AND INSTALLATION 3.1 Some General Comments About Station Design 3.2 Instrumentation 3.3 Design and Construction of Sensor Vault 3.4 Power System 3.5 Digitizer and Telemetry

3-1 3-1 3-2 3-2 3-3 3-3

4.0

STATION METADATA AND DATA MANAGEMENT 4.1 Location and Instrumentation 4.2 Instrument Response Files and Calibration 4.3 Data Management

4-1 4-1 4-1 4-1

5.0

PRELIMINARY EVALUATION OF DATA QUALITY 5.1 Noise Analysis of Broadband Data 5.2 Example Waveforms from Teleseismic and Local Earthquakes 5.3 Troubleshooting a “Data-Gap” Problem

5-1 5-1 5-2

6.0

MANAGEMENT DETAILS 6.1 Maintenance and Operation of CCUT 6.2 Title to Equipment 6.3 Data Availability

6-1 6-1 6-1

7.0

REFERENCES

7-1 iii

TABLE OF CONTENTS (continued)

___________________________________________________________________________ LIST OF TABLES Table 1-1

Chronology for Installation of Station CCUT

LIST OF FIGURES Figure 1-1

Map of ANSS/USArray national backbone network of broadband seismograph stations, June 2006

Figure 1-2

Map showing the location of station CCUT with respect to the distribution of stations in the University of Utah’s regional/urban seismic network, June 2006

Figure 2-1

Photo showing the location of station CCUT with respect to surrounding topography and underlying massive porphyritic intrusive rock of Tertiary age

Figure 2-2

Location map for station CCUT

Figure 2-3

Photo showing the site of station CCUT (prior to construction) and line of sight to a radio repeater site

Figure 3-1

Photo showing one of three “barrels” used for below-ground enclosures

Figure 3-2

Photos showing excavation of sensor vault

Figure 3-3

Schematic cross section and photo showing details of sensor vault

Figure 3-4

Photo giving an overview of elements of station CCUT

Figure 3-5

Photos illustrating construction details of the power system

Figure 3-6

Photos illustrating selected details of the digitizer-telemetry system onsite

Figure 3-7

Photos showing UUSS radio repeater at BLM communications site 5.5 km to the eastnortheast of station CCUT and details of electronics

Figure 3-8

Photos showing details of radio receiver site in Cedar City

Figure 5-1

Comparison of revised PDF noise levels for seismic test data recorded in Autumn 2005 at two candidate sites for station CCUT

Figure 5-2

Photos showing the installation of a Guralp CMG-40T broadband seismometer used to sample data displayed in Figure 5-1

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TABLE OF CONTENTS (continued)

___________________________________________________________________________ Figure 5-3

PDF noise plots for station CCUT (STS-2) for a seven-day period, June18–25, 2006

Figure 5-4

Composite figure showing PDF noise plots for three-component broadband data at station CCUT before and after completion of the station together with corresponding plots for station SRU

Figure 5-5

Raw and displacement broadband seismograms recorded at CCUT from an MW 6.2 earthquake in the Aleutian Islands (Δ = 50º) on June 27, 2006

Figure 5-6

Signal and noise spectra calculated from the raw data of Figure 5-5

Figure 5-7

Raw broadband seismograms recorded at CCUT for an ML 2.2 local earthquake on June 26, 2006, located 72.5 km away

Figure 5-8

Plots of gaps per day, from the IRIS Quack system, for each of the three broadband channels at CCUT for the two-month period May 1–June 30, 2006

APPENDICES Appendix A

Metadata and Response Files for Station CCUT

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EXECUTIVE SUMMARY This report summarizes a cooperative project to fund and install a permanent high-quality broadband seismograph station near Cedar City, Utah (station code CCUT), as part of a “national backbone” network of 100 uniformly spaced broadband stations in the continental United States. This nationalscale network is a key element of the Advanced National Seismic System (ANSS) and also is intended to serve as a reference network for EarthScope’s USArray project, managed by the Incorporated Research Institutions for Seismology (IRIS) and funded by the National Science Foundation. The project was undertaken jointly by the University of Utah Seismograph Stations (UUSS), IRIS, and the U.S. Geological Survey (USGS). UUSS took the lead in siting and installing station CCUT with the cooperative involvement of the USGS and with partial funding from IRIS/NSF in the amount of $30,362. Total direct costs for the completed project are estimated to have totaled approximately $62,000 for equipment, hardware, supplies, travel, and labor. Of the total direct costs, IRIS/NSF contributed 42%, USGS contributed 32% (primarily in equipment), and UUSS contributed 26% in state funds. CCUT will be operated and maintained as a cooperative UUSS/USGS station under the ANSS program. The essential seismic instrumentation at station CCUT includes: (1) a REF TEK 6-channel, 24-bit digital seismic recorder (Model 130-01/6) with GPS receiver/clock and 1 GB flash memory, (2) a Streckheisen triaxial broadband seismometer (Model STS-2), and (3) an Applied MEMS, Inc., triaxial micro-electro-mechanical system (MEMS) force-balance accelerometer (REF TEK Model 131A-02/3) with ±3.5g full scale. The sensors are set in a buried vault on bedrock made up of Tertiary porphyritic igneous rock associated with a shallow hypabyssal intrusive. CCUT is located in the Pine Valley Ranger District of the Dixie National Forest; a special use permit from the U.S. Forest Service was issued to the University of Utah for constructing, operating, and maintaining the station. Continuous seismic data from CCUT are telemetered by digital spread-spectrum radio first to a radio repeater 5.5 km distant and then another 25 km to Cedar City, where an Internet connection is made to the UUSS network operations center on the University of Utah campus in Salt Lake City. From there, continuous waveform data are forwarded to the USGS National Earthquake Information Center (NEIC) via an Earthworm export module and to the IRIS Data Management Center (DMC) through one of the UUSS Earthworm public waveservers. The period of performance for this IRIS/NSF award was June 1, 2005–May 31, 2006. CCUT was first installed in a temporary mode and was delivering continuous data to both the IRIS DMC and the USGS NEIC on March 1, 2006. Installation of the six-component broadband/strong-motion station was completed on May 25, 2006, and the station was fully operational in a permanent mode on June 2, 2006. A preliminary evaluation of the quality of the completed station, based on spectral analyses of recorded earthquakes and background seismic noise, indicates that CCUT indeed is a high-quality station, possibly as good as station SRU—a premium backbone station in east-central Utah. Extensive details are provided in the report relating to the installation of station CCUT—including site selection, design and construction of the sensor vault, professionally designed lightning protection, power system, and telemetry. The documentation and technical descriptions should be of interest to others involved in siting and installing similar seismic stations. vi

ACKNOWLEDGMENTS The success of this project would have been impossible without the supportive involvement of Kent Anderson and Rhett Butler of the Incorporated Research Institutions for Seismology (IRIS) and of Harley Benz and Alena Leeds of the U.S. Geological Survey (USGS). We owe special thanks to many staff members of the University of Utah Seismograph Stations (UUSS) who were involved in completing various project tasks; in particular, we thank Ken Whipp for invaluable help with site reconnaissance, site construction work, and field engineering; Gordon Johansen for his hard work in field construction at the station and relay sites; Ali Moeinvaziri for computer support; and Michelle Kline and Paul Roberson for help with graphics. We also thank Pamela Christensen of the Pine Valley Ranger District of the Dixie National Forest, U.S. Forest Service, for help getting a special use permit for the installation and operation of station CCUT, and Elaine Robinson and Marcus Brinkerhoff of the U.S. Bureau of Land Management (BLM) for permission to install radio-repeater equipment on a BLM communications structure in the Harmony Mountains. The following individuals kindly helped us to establish an Internet connection at a state office building in Cedar City: Bill Lund, Utah Geological Survey; Dave Yardley, Iron County Clerk; and Walt Rodriguez and Charmain Malan, Utah Department of Natural Resources. Greg Steiner of VLF Designs, Germantown, Tennessee, designed the special lightning-protection features we used in constructing station CCUT. Partial funding for this project was provided by IRIS, Subaward Agreement No. 383 under National Science Foundation Cooperative Agreement NO. EAR-0004370. Some government-furnished equipment (broadband sensor and accelerometer) was provided by the USGS. Contributing support was also provided by the State of Utah, under a line-item appropriation to UUSS, and by the USGS under Cooperative Agreement No. 04HQAG0014, which provides support to UUSS for implementing the Advanced National Seismic System in the Utah region.

vii

1.0 INTRODUCTION 1.1 Background The U.S. Geological Survey (USGS) and the Incorporated Research Institutions for Seismology (IRIS) share a common goal of achieving the installation of a “national backbone” network of 100 uniformly spaced broadband seismograph stations in the continental U.S. (Fig. 1-1). For the USGS, the backbone is the key national-scale element of an Advanced National Seismic System (ANSS). For IRIS, the national backbone is intended to serve as a reference network for USArray—the rolling transportable array of 400 broadband seismometers managed by IRIS that forms a major component of the EarthScope project funded by the National Science Foundation (NSF). As of early 2005, one of the unfilled “holes” in the ANSS/USArray national backbone network was a station site near Cedar City in southwestern Utah that appeared on planning maps as “CCUT” (see Fig. 1-1). The completed station that forms the subject of this report retains that station code. The University of Utah Seismograph Stations (UUSS) had a particular interest in CCUT—first, because we needed additional seismographic coverage in southwestern Utah and second because we wanted to ensure the outcome of a high-quality low-noise station. CCUT promised to be a key station in the Utah region for earthquake monitoring, moment-tensor control, and ShakeMap control (see the regional-network map in Fig. 1-2). Our network field engineers had considerable experience in site selection and field engineering of high-quality broadband stations in the Utah region. So we took a proactive role in pursuing CCUT as a cooperative venture with the USGS and IRIS. 1.2 Cooperative Funding of Station CCUT In May 2005, the University of Utah submitted a proposal to IRIS requesting partial funding to enable the installation of CCUT as a six-component broadband/strong-motion seismograph station. The requested funds were primarily for labor, travel, and construction costs related to the installation of the new station and completion of a telemetry link to a telecommunications node in Cedar City, Utah. The budget also included $10.1K for the purchase of a REF TEK 130-01/6 data logger. UUSS proposed to take the lead in siting and installing the station with the cooperative involvement of the USGS. The intent was to operate and maintain CCUT as a cooperative UUSS/USGS station under the ANSS program. As part of the national backbone network, the station would jointly serve ANSS and NSF’s EarthScope/USArray project. In June 2005, IRIS awarded an amount of $30,362 to the University of Utah, as requested, to cooperatively fund station CCUT. (For reference below, the award amount included $25,996 in direct costs and $4,366 in indirect costs.) As part of the cooperative venture, the USGS provided sensors and UUSS contributed partial costs for labor, travel, and supplies. The costs for this completed project are estimated to have totaled ~$62K in direct costs (besides the $4.4K in indirect costs paid to the University of Utah by the IRIS award). Of the total direct costs, IRIS contributed $26K (42%), USGS contributed $20K in equipment (32%), and UUSS contributed $16K (26%) in funds from the state of Utah. The UUSS contribution included $5K in labor and travel costs for site exploration and noise testing in 2003–2004 and about $11K (mostly in personnel costs) in 2005–2006 for fieldwork, work in our network operations center to record and get qualitycontrolled data to IRIS and the USGS, and for project management.

1-1

1.3 Project Objectives The primary goal of this project was to site and install a broadband/strong-motion seismograph station near Cedar City in southwestern Utah that would have low-noise characteristics, telemeter data continuously in real time, and be a high-quality permanent addition to the ANSS/USArray national backbone network. Project objectives/tasks included the following: • • • • • • • • • •

Site selection and noise testing Site permitting Engineering of a real-time telemetry link from the station site to the UUSS network operations center in Salt Lake City Purchase/acquisition of station instrumentation Construction at (1) the station site (including customized sensor vault and specially designed lightning protection), (2) the radio repeater site, and (3) the telecommunications junction with the Internet in Cedar City Installation and calibration of seismographic equipment Completion of telemetry routing to UUSS and configuration of data recording Continuous data streaming to the USGS’s National Earthquake Information Center in Golden, Colorado Submission of continuous data to the IRIS Data Management Center in SEED format Evaluation of signal and data quality

1.4 Project Timeline The period of performance for this IRIS subaward was from June 1, 2005 to May 31, 2006. Table 1-1 outlines the chronology for the installation of station CCUT, extending from initial reconnaissance for candidate sites as early as 2002 to completion of the station installation on May 25, 2006 (the station was fully operational on June 2, 2006, after a GPS clock repair). The timeline reflects many of the realities of planning and installing a permanent, high-quality broadband station in the Intermountain area, particularly on a cooperative basis. These realities include careful noise testing, the lengthy time to secure a site-use permit on federal land, coordination among funding partners, the usual constraints of winter weather, and “shakedown” typically required when the telemetry scheme is complex. Given the challenges described in the timeline, our field staff did an admirable job of (1) achieving a first-stage installation of CCUT under winter field conditions during November 2005–February 2006 and (2) completing the final station installation on schedule. 1.5 Scope of this Report

To fulfill the terms of our IRIS agreement, this report describes the completed activities funded by this award—notably the successful installation and operation of station CCUT. Besides documenting essential information such as station metadata, we describe other details that we believe will be of interest to others involved in siting and installing similar seismic stations. In section 2.0 we review the process of site selection, followed in section 3.0 by a description of technical details of the station instrumentation and installation, including details of the sensor vault design and construction. Next, section 4.0 provides station-metadata and data-management information. Section 5.0 then describes a preliminary evaluation of the evidently high quality of station. Finally, we call attention to some project-management details in section 6.0, including the future maintenance and operation of CCUT and the title to permanent equipment. 1-2

Table 1-1 Chronology for Installation of Station CCUT Date

Milestone/Other Detail

2002–2004

Reconnaissance by UUSS field staff for candidate sites for national backbone station CCUT in the general vicinity of Cedar City, Utah—including evaluation of sites at Page Ranch, Ox Valley, and Upper Grants Ranch

2004—Aug.–Sept.

Comparative broadband noise testing at candidate sites near Ox Valley and Upper Grants Ranch (ultimately selected site)

2004—Dec. 6

Teleconference involving UUSS and USGS parties to decide on site selection, instrumentation, and other issues for installing CCUT

2004—December

Site-use application for CCUT submitted to U.S. Forest Service by UUSS

2005—Feb. 17

Draft proposal to Rhett Butler of IRIS for partial funding of CCUT

2005—April 13

Permission from U.S. Bureau of Land Management (BLM) to install a radio repeater at BLM communications site in the Harmony Mountains

2005—May 11

Formal UUSS proposal to IRIS

2005—early June

IRIS Subaward Agreement to University of Utah for CCUT; authorized signatures completed on June 15, 2006

2005—late June

REF TEK 130-01/6 data logger ordered

2005—Oct. 19

Data logger received from REF TEK

2005—Oct. 19

Oral approval from U.S. Forest Service allowing UUSS to proceed with site construction of CCUT on or after Nov. 6, 2005

2005—early Nov.

STS-2 broadband sensor received by UUSS from USGS

2005—Nov. 22

Radio repeater installed at BLM communications site in the Harmony Mts.

2005—Dec. 20–21

Despite challenge of winter snow conditions, initial site construction work done at CCUT

2005—Dec. 22

Installed master radio and connection to Internet at Utah Geological Survey regional office in Cedar City

2006—Jan. 9

CCUT broadband sensor installed in a temporary vault; station up and recording but unstable and requiring further shakedown through January and early February

2006—Feb. 23

Recording of CCUT stable

2006—March 1

Dataless SEED volume, including information for CCUT, provided to IRIS DMC; start of streaming of CCUT data to USGS/NEIC via Earthworm export

1-3

Table 1-1 (continued) Chronology for Installation of Station CCUT Date

Milestone/Other Detail

2006—March 3

Formal special use permit for CCUT issued by U.S. Forest Service; authorized signatures completed on Apr. 28, 2006

2006—March 31

MEMS accelerometer received by UUSS from USGS

2006—Apr. 25–26

After snowstorms in March and early April, UUSS field staff finally able to construct a permanent sensor vault at CCUT; concrete left to cure

2006—May 25

Station installation completed: Broadband sensor and accelerometer installed in permanent vault and power system with engineered lightning protection completed; GPS clock failed when station power turned on

2006—June 2

GPS clock replaced; station fully operational

1-4

Figure 1-1. Map of ANSS/USArray national backbone network of broadband seismograph stations, June 2006. Labeling indicates the location of station CCUT in southwestern Utah. (Base map courtesy of Harley Benz, USGS)

1-5

Figure 1-2. Map showing the location of station CCUT (lower left) with respect to the distribution of stations in the University of Utah’s regional/urban seismic network, June 2006. (Note: Although station KNB, owned and operated by Lawrence Livermore National Laboratory, is relatively close to CCUT, it has not provided data to the USGS National Earthquake Information Center or to the IRIS Data Management Center since October 2003.) 1-6

2.0 SITE SELECTION 2.1 Background As early as 2002, UUSS undertook to help the USGS find a site for a broadband national backbone station in southwestern Utah. The USGS wanted a site location within about 50 km of Cedar City, Utah. Originally, it also wanted a site with AC power for satellite telemetry. With this guidance, our field staff made several scouting trips to the area in late 2002 and 2003, including a trip with Alena Leeds of the USGS. Finding a reasonable site with AC power was a problem. One possible site was found at Page Ranch, 34 km west-southwest of Cedar City, but the availability of AC power inherently meant a compromise in terms of accepting some nearby cultural and minor traffic noise. When it later became apparent that the USGS was considering relaxing the power and telemetry requirements for national backbone stations, further action on the Page Ranch site was suspended. A more remote quieter site was preferred. In the summer of 2004, the USGS gave us new guidelines for a national backbone station that allowed the possibility of onsite solar power and non-satellite telemetry. Freed from the AC-power constraint, we expanded scouting efforts in the Cedar City area to find remote but accessible outcrops of geologic units that, from experience, were likely to be suitable for low-noise seismographic recording. Issues such as permitting, wintertime access, exposure to the elements, and telemetry options were also considered. In particular, the feasibility of a digital radio link to an Internet connection in either Cedar City or Enterprise, 59 km to the west, greatly opened up our siting options. Two candidate sites were identified—one on a ridge south of Enterprise (“Ox Valley” site) and another (“Upper Grants Ranch” site) approximately 30 km southwest of Cedar City in the western part of the Harmony Mountains. Both sites were on outcrops of Tertiary porphyritic intrusive rock. 2.2 Noise Testing, Autumn 2004 At the Ox Valley and Upper Grants Ranch sites, continuous seismic data were recorded for approximately one week at each site in August–September 2004 using a 30-sec-period Guralp CMG40T seismometer and REF TEK digitizers (16-bit DAS at Ox Valley and 24-bit DAS at Upper Grants Ranch). The data were analyzed using probability density functions (PDF; McNamara and Buland, 2004). Our original PDF results from the comparative noise testing showed similar noise levels at both sites. Subsequently, we discovered that the PDFs for the Ox Valley noise data were computed incorrectly because a wrong constant was used for the 16-bit digitized data. The corrected PDFs show noise levels about 10 dB lower in the 10–100 sec range compared to the test data from the Upper Grants Ranch site (discussed below in section 5.1). However, these results would not have changed our decision to select the latter site. The noise tests in 2004 demonstrated sufficiently low noise levels at both sites, but we preferred the Upper Grants Ranch site for the following reasons. First, it allowed easier wintertime access. Second, it was situated on a relatively massive outcrop of large areal extent (Fig. 2-1) that had a lower fracture density than the same rock at the Ox Valley site. Third, it was a more sheltered site and we judged that it would be less susceptible to wind noise than the ridge-top location of the Ox Valley site. In our original proposal to IRIS dated May 11, 2005, we showed noise results for the verticalcomponent test data from the Upper Grants Ranch site, which we put forward as our site of choice. We noted that the noise results for the horizontal components were very similar and said: “The noise results [are] below the high-noise model (McNamara and Buland, 2004), and the absolute power levels should decrease with a permanent installation. The very

2-1

narrow power range evident in the PDF indicates that this should be a stable and quiet site (D. McNamara, personal communication, 2004).” In section 5.1 we revisit the PDFs for the 2004 noise testing at the Upper Grants Ranch site to compare the 2004 PDFs with those from the finally installed station. 2.3 Location and Site Conditions of Station CCUT Station CCUT is located approximately 30 km southwest of Cedar City, Utah, in the western part of the Harmony Mountains. As shown in a location map in Figure 2-2, the station is approximately 1.9 km straight-line distance northeast of Upper Grants Ranch1; the closest distance to the unimproved dirt road shown on the map is about 200 m. The GPS-determined coordinates for station CCUT (see Appendix A) are 37º 33.040′ N. latitude, 113º 21.765′ W. longitude. A station elevation of 2124 m was determined from a 1:24,000 topographic map having a 20-ft contour interval. The foundation rock at station CCUT is a porphyritic silicic igneous rock of Tertiary age formed as part of a shallow hypabyssal intrusive. Figure 2-3, a photo of the station site taken prior to construction, shows the foundation rock, which would be classified as NEHRP VS30 Site Class “A” (hard rock). 2.4 Site-Use Permits Station CCUT is located in the Dixie National Forest, managed by the Pine Valley Ranger District of the U.S. Forest Service. UUSS formally applied to the Forest Service for a special use permit in December 2004, following a teleconference between UUSS and USGS parties on December 6, in which a decision was made to go ahead with the Upper Grants Ranch site. After a long process, including required archeological and other impact assessments, we were given oral permission by the Forest Service in October 2005 to proceed with site construction of CCUT. A written permit was issued to the University of Utah later in March 2006 (Special Use Permit PNV008301). In late 2004–early 2005, we also began a permitting process to locate a radio repeater on a mountain top 5.5 km to the east-northeast of CCUT (see Fig. 2-3), where the U.S. Bureau of Land Management (BLM) has communications infrastructure. After numerous communications with the BLM and a visit to their office in Cedar City, a decision was made by the BLM in April 2005 that we did not need our own Right of Way permit for our radio repeater. We were given permission to locate our equipment in a stand-alone fashion—not using their power and not placing equipment inside a BLM hut at the site (see Fig. 3-7). Oral permission to install communications equipment at a county-owned building in Cedar City where the Utah Geological Survey has a regional office and where we planned to connect to the Internet was given by David Yardley, Iron County Clerk, during an early scouting trip. The Internet connection was arranged with our contacts at the State of Utah Information Technology Services during the summer of 2005.

1

The site of Upper Grants Ranch labeled on Figure 2-2 apparently is the vestige of a former homestead. There are no buildings now at this site. At Grants Ranch (Fig. 2-2), there is a lodging that, to appearances, is occasionally occupied.

2-2

Figure 2-1. Photo looking to the north with yellow dot (upper left) marking the location of station CCUT. Most of the topography in the photo is underlain by massive porphyritic intrusive rock of Tertiary age.

2-3

CCUT x

Figure 2-2. Location map for station CCUT (marked by red X in upper right of figure). Coordinates: lat. 37º 33.040' N, long. 113º 21.765' W, elevation 6970 ft (2124 m). Site is approximately 30 km southwest of Cedar City, Utah, in the western part of the Harmony Mountains. All roads shown in the figure are unimproved dirt roads. Straight-line distance from Upper Grants Ranch (in the center of the map) to the site is approximately 1.9 km (1.2 mi.). [Note: There are no buildings at “Upper Grants Ranch,” apparently the site of a former homestead, and at Grants Ranch there is a lodging that, to appearances, is occasionally occupied.]

2-4

Figure 2-3. View from site of station CCUT (prior to construction) looking to the east-northeast towards planned radio-repeater site. Tertiary porphyritic intrusive rock underlies the site and forms the surrounding topography.

2-5

3.0 INSTRUMENTATION AND INSTALLATION 3.1 Some General Comments About Station Design Before describing details of our installation of station CCUT, we offer some general comments about factors that influenced our decision-making in designing the permanent station: 1.

Our selected site was inaccessible to heavy equipment such as a backhoe. This was one of the basic trade-offs in finding a low-noise site on competent bedrock, away from cultural noise and hidden as well as possible from potential vandalism.

2.

From decades of experience, our field staff believes that a custom-designed station that deals with the particular circumstances of an individual site is generally better than a "standardized" station—with the possible exception of a heavy-duty sensor vault when a site is accessible to a backhoe.

3.

Part of our station-design philosophy is that no more infrastructure should be installed than is necessary. (We have a good reputation with federal and state agencies from which we seek siteuse permits in Utah, in part because they know they can trust us to be environmentally sensitive and as non-intrusive as possible on public lands. In Utah, 65% of the land is owned by the federal government.) For example, although tower-mounted equipment may present a professional appearance, there was no compelling need for a tower at CCUT. We guessed that snow depth would be less than a meter in a heavy snow year, so we designed a special mount for solar panels that would be high enough but would hide their visibility from a distance. Also, we chose to mount a radio antenna in a tree, which serves just as well as a mast or tower section.

4.

The dry climate and alkaline soils of Utah make for ease of station design and installation in some respects (e.g., less concern about water). However, these same conditions call for greater attention to properly grounding equipment for surge protection, which influences many aspects of the station design.

5.

To safeguard the equipment investment at CCUT—as well as at our other costly broadband stations—we contracted professional help to design a robust lightning-protection system. For good grounding and to minimize spurious noise on the DAS inputs, the REF TEK recorder and radio were put in a partially buried steel barrel close to the sensor vault, instead of, say, in a box mounted above ground. The metal barrel provides the most effective grounding in a setting like this. Sensor-to-DAS cables are best kept as short as to prevent pickup of unwanted signals induced by time-varying changes in the atmosphere, notably lightning.

6.

From long experience we’ve found that, besides having an adequate solar array, battery longevity (and hence station reliability) is dramatically enhanced by ensuring that the dry-cell type of batteries used in our solar-power systems are kept at a uniform temperature. Keeping batteries from getting hot is particularly important. We have a simple battery “vault” design (described in section 3.4) that achieves this goal and works well in Utah,2 although it may not be suitable in wetter climates. Advantages of our insulated vault design include: (1) keeping the batteries from getting too cold in winter, which temporarily decreases their capacity exactly when needed the most; (2) reducing the number of temperature cycles the batteries go through, which decreases battery life; (3) avoiding different charging chemistry in parts of a battery—for example, where one side of the battery in an above-ground box gets hot from the sun beating on the box while the

2

At many of our network stations, the batteries have now been operating in good condition for over ten years using our scheme for insulated battery storage. At one site, a load test was done on a 12-year-old battery and it tested better than a new one brought to the site for its replacement. Before implementing our vault design it was common for batteries to fail within 1–3 years after installation.

3-1

opposite side may still be cold from the nighttime; (4) adequate ventilation, which a tight box does not provide; (5) reduced condensation; and (6) effective grounding in our dry climate and alkaline soils by putting the batteries in a metal barrel. 7.

Based on discussions with the USGS in December 2004, the option of constructing CCUT without satellite telemetry was judged to be attractive for the overall robustness of the national backbone system. From the UUSS point of view, reliable telemetry without recurring telecommunications costs was an important design consideration.

3.2 Instrumentation The essential seismic instrumentation at station CCUT includes: (1) a REF TEK 6-channel, 24-bit digital seismic recorder (Model 130-01/6) with GPS receiver/clock and 1 GB flash memory, (2) a Streckheisen triaxial broadband seismometer (Model STS-2), and (3) an Applied MEMS, Inc., triaxial micro-electro-mechanical system (MEMS) force-balance accelerometer (REF TEK Model 131A-02/3) with ±3.5g full scale. (See Appendix A, Table A-1, for sensor sensitivity specifications and serial numbers for the seismic recorder and sensors.) Accessory equipment at CCUT includes solar panels and batteries, a spread-spectrum radio and antenna, and site hardware for suitably enclosing instrumentation, for cabling, and for lightning protection. 3.3 Design and Construction of Sensor Vault Timing.—The STS-2 broadband sensor was first installed at CCUT in a temporary fashion, under winter conditions, on January 9, 2006, and it operated this way until ground conditions allowed the construction of a permanent sensor vault in late April and May of 2006 (see Table 1-1). From January 9 until May 25, 2006, the STS-2 was simply in a shallow rock hole and covered by an inverted insulated water cooler that was partly buried with soil. A permanent sensor vault was constructed at CCUT April 25–26, 2006. Digging, jack-hammering, and concrete work was done at that time. After allowing a few weeks for the concrete to cure, the final vault and power system were completed on May 25. Lightning protection.—CCUT is the first station we have installed to incorporate a professionallydesigned scheme for robust protection from serious electrical surges due to lightning. The design work was done by Greg Steiner of VLF Designs, Germantown, Tennessee. In general terms, all barrels and solar panel frames are grounded together with #6 wire, and there is surge protection at each end of the cabling between the solar panels and the charger-battery as well as at each end of the power cable between the battery and the digitizer barrel. On the coaxial cable from the antenna, there is also a 1/4-wave shorting stub (i.e., a piece of cabling 1/4 wavelength long that essentially acts as a bandpass filter for the frequency of interest while shorting all others to ground). For want of a better word, we use the term “barrel” herein to refer to cylindrical sections of corrugated steel culvert, 24" diameter x 24" or 18" height, to which 1/2" wire mesh has been fastened to the bottom (Fig. 3-1). The purpose of the wire mesh is to act as a Faraday cage in order to keep any electrical surges which may enter from going through any instruments or electronics inside the barrel to ground. Vault construction.—The sensor vault was excavated on the north side of a low bedrock ledge (Fig. 32, lower left) in order to minimize sun exposure and allow whatever snow that accumulates in winter to drift in and add more thermal stability. A portable jackhammer was used to excavate about two feet of rock, removing weathered rock in the process and opening a hole for emplacing and burying one of the culvert barrels (Fig. 3-2, upper right). After digging out the hole we cleaned the foundation rock 3-2

and set one of the steel culverts with a wire-mesh base into it; we then poured in two 80-lb bags of concrete, embedding the wire-mesh base into the concrete and making sure the concrete was well bonded to the bedrock. A drain hole and tubing were installed on the downhill side of the barrel in case of any water seepage into the barrel. Figure 3-3 shows relevant details of the sensor vault. A ceramic tile (1ft square) was embedded in the concrete, rough side up, to serve as a foundation for the STS-2 sensor. This foundation was to avoid placing the sensor’s aluminum feet directly on the concrete, thereby preventing their corrosion. The Applied MEMS accelerometer, which has stainless-steel feet, is bolted to the concrete. Cabling to the REF TEK recorder, located in an adjacent barrel approximately 2 feet away, goes through a conduit to that barrel. For thermal stability, we considered filling the conduit with some spray foam but decided that would inevitably present some maintenance headaches. Instead, we used cloth-filled plastic bags tightly squeezed into both ends of the conduit, which should adequately stop air movement. The interior sides of the barrel are insulated with two cylindrical wraparounds of 1/2" polyethylene foam (1" total thickness), and the inside of the lid is insulated with 4" (two 24"-diameter disks) of polystyrene foam, which rests on top of the side foam. After sensor operation was confirmed, a steel lid was put in place and the entire barrel was buried with dirt, approximately 2–3 feet deep (see Fig. 33). The sensors consequently are 4–5 feet underground. We did not put a cloth bag filled with sand into the barrel to fill the void space, as USGS staff at the Albuquerque Seismological Laboratory recommend, but we can do that at a later date if desired. This step has the advantage of increasing thermal stability as well as preventing the broadband sensor from moving if significant ground motion occurs. It has the disadvantage, however, of retaining moisture. 3.4 Power System Power is provided by two sealed Absorbed Glass Mat (AGM) 12-volt batteries (100 amp-hr) charged by two 80-watt solar panels and a Flexcharge NC30L12 charging regulator. The power system is located 50 feet north of the digitizer/sensor barrel. The panels are mounted to a custom-welded rack made of Unistrut, which is bolted into bedrock. The photo in Figure 3-4 shows the structure and location of the solar-panel rack. Additional photos in Figure 3-5 illustrate some of the construction details of the power system. For reasons given in section 3.1 (Comment No. 8), the batteries were placed below ground in a barrel next to the solar-panel rack. Similar to the sensor barrel, the battery barrel is a cylindrical section of a corrugated steel culvert (24" diameter x 18" height) with a wiremesh base embedded in concrete. The wire-mesh base, together with surge protection electronics bolted to the side of the barrel, provide lightning protection. The interior of the barrel is insulated with two cylindrical wraparounds of 1/2" polyethylene and 2" polystyrene disks on top and bottom, and it has a small drain hole on the downhill side. 3.5 Digitizer and Telemetry Onsite elements.—Data from the sensors at CCUT are digitized by the REF TEK 130-01/6 seismic recorder, which is connected via Ethernet to an Intuicom Ethernet Bridge spread-spectrum radio modem. The seismic recorder, radio, and the STS-2 “host box” are all installed in a barrel (referred to as the “digitizer/radio barrel”) located less than one meter west of the sensor vault (Fig. 3-6, upper left). Like the sensor vault and battery barrel, the digitizer/radio barrel is a section of corrugated steel culvert, in this case 24" diameter x 18" deep, with a wire-mesh base embedded in concrete and surgeprotection electronics bolted to the side of the barrel (Fig. 3-6, upper right). The interior of the barrel is insulated with two cylindrical wraparounds of 1/2" polyethylene and 2" polystyrene disks on top and bottom; it also has a foam shelf to keep everything off the bottom of the barrel in case water gets in. As shown in Figure 3-6 (lower left), the GPS clock/receiver is mounted on a T-post beside the digitizer/radio barrel. A 9-dBd Yagi radio antenna is mounted on a nearby piñon pine trunk (Fig. 3-6, 3-3

lower right). Cables to the antennas run out of the barrel through aluminum flex conduit which follows the cables up high enough off the ground to prevent rodent access (allowing for some snow accumulation). Offsite elements.—Telemetry options were carefully investigated as part of the site selection process for CCUT. For the Upper Grants Ranch site, we determined at an early stage the feasibility of using digital radio from the site to Cedar City via a radio repeater at the BLM mountaintop communications site described in section 2.4. In Cedar City, we had access to an Internet connection at a state office building. When the U.S. Forest Service assured us in late October 2005 that we would be issued a site-use permit for the Upper Grants Ranch site, we proceeded to plan and install the radio repeater because the BLM mountaintop site posed the prospect of difficult wintertime access. The repeater site is 5.5 km to the east-northeast of CCUT; its coordinates are: 37º 33.695′ N. latitude, 113º 18.144′ W. longitude, elevation 2530 m. There the BLM has a tower about 10 m high, a small locked hut, and a solar array (Fig. 3-7). At the repeater site we installed a 20-watt solar panel and a rugged 6-dBd omni-directional antenna mounted on a 2"-diameter mast on the northeast side of the BLM hut. A 100 amp-hr AGM battery, charging regulator (VLF Designs SR-2), and radio (Intuicom Ethernet Bridge) are housed in an 18"diameter barrel (a steel culvert section similar to those described earlier), which is buried under rocks outside the edge of the BLM hut. Because of the exposed mountaintop location, extensive grounding of everything was done for lightning protection. (Note: We initially considered siting and building our own radio repeater—until we discovered the BLM communications site. Despite the convenience of the BLM site, it is vulnerable to vandalism. Our solar panel at the BLM site was stolen in January 2006, so the replacement was welded to the antenna mast. If vandalism problems recur, we will move our repeater to a more remote site.) Radio signals from the radio repeater at the BLM site are transmitted 25 km northeast to a countyowned building in Cedar City (Fig. 3-8), where the Utah Geological Survey (UGS) has a regional office and where an Internet connection is made. The Internet connection was brought up on January 9, 2006. Equipment at this location includes the master radio (Intuicom Ethernet Bridge) located in a telecom closet next to a UGS office, a 9-dBd Yagi antenna mounted on the outside wall of the building, and a Netgear RP614 router used to “hide” the radio (a Layer 2 bridge) from network traffic located in the basement where the state has it's router/switch (the radio gets overloaded if it sees too much network traffic). A minor amount of debugging was required.

3-4

Figure 3-1. Photo showing one of three “barrels” used at station CCUT for below-ground enclosures. Each barrel consists of a cylindrical section of corrugated steel culvert 24" in diameter and either 24" or 18" in height. For lightning protection, a 1/2" wire mesh is fastened to the bottom, thus serving as a Faraday cage to keep any electrical surges from going through instruments or electronics inside the barrel to ground. For each barrel at CCUT, the wiremesh base was embedded in concrete, bonded to the underlying bedrock.

3-5

Figure 3-2. Photos showing excavation of sensor vault at station CCUT using a portable jackhammer (lower left). Approximately two feet of rock was excavated to create a hole with a solid bedrock base (upper right) for emplacing a steel barrel to enclose the sensors.

3-6

Figure 3-3. Schematic cross section (lower left) showing details of the sensor vault at station CCUT. Inset photo (upper right) shows view from above into the corrugated steel culvert before burial; note: ceramic tile beneath STS-2 was not aligned in a preselected compass direction. 3-7

D C B

A

Figure 3-4. Photo (looking south) giving an overview of elements of station CCUT, including: (A) solar panels mounted on a custom-welded Unistrut rack, (B) buried sensor vault, (C) digitizer/radio barrel (steel lid visible at ground surface), and (D) T-post on which GPS receiver/clock is mounted.

3-8

Figure 3-5. Photos illustrating construction details of the power system. Installing 3/4" copper conduits from solar panels to the battery barrel (upper left). Close-up of layout (upper right): one conduit contains solar-panel wires and ground wire; the other, DC power cable to seismic recorder and ground wire. View from above into insulated battery barrel (lower left) showing AGM batteries, charging regulator, and surge-protection electronics bolted to the side of the barrel. View of completed construction (lower right) with battery barrel covered with soil for added thermal insulation. 3-9

Down

Figure 3-6. Photos illustrating selected details of the digitizer-telemetry system onsite at station CCUT. (Upper left) View from above into the digitizer/radio barrel showing the REF TEK recorder with a black PDA sitting on top of it; the STS-2 host box can be seen on the right side of the barrel; surge-protection electronics are on the left side beneath an aluminum drip cover. (Upper right) Detail of surge-protection electronics, including ground wires at top, circuitry at right, and ¼-wave shorting stub atop the Intuicom radio (before coaxial cable was connected to the radio). (Lower left) View of vertical T-post with attached GPS receiver/clock immediately to the left of the digitizer/radio barrel (lid visible at ground level); dirt pile in foreground covers the sensor vault. (Lower right) Yagi radio antenna mounted on tree trunk.

3-10

Figure 3-7. (Upper right) Photo showing UUSS radio repeater at BLM communications site on mountaintop 5.5 km to the east-northeast of station CCUT (for scale, note 10-ft ladder leaning against right side of green enclosure). UUSS antenna mast, with attached solar panel and an omni-directional radio antenna, is at the left of the green enclosure. From this site, radio signals from CCUT are re-transmitted to the site of an Internet connection in Cedar City, 25 km to the northeast. (Lower left) View from above into 18"-diameter insulated barrel, buried near the UUSS antenna mast; inside the barrel are a 12-volt AGM battery with an SR-2 charging regulator, an Intuicom radio in the upper right, and surgeprotection electronics mounted on the side of the barrel in the upper part of the view.

3-11

Figure 3-8. (Upper left) Photo showing Yagi radio antenna mounted on the outside wall of a countyowned building in Cedar City, Utah, at 88 East Fiddler Canyon Road; digital radio signals from station CCUT received at this point from the radio repeater at the BLM communications site (Fig. 3-7) are linked to the Internet. (Lower right) Photo showing an Intuicom master radio mounted in a telecommunications closet inside the building; the black coaxial cable atop the radio is connected to the Yagi antenna and the blue-gray network cable connects to a state Internet node in the basement of the building.

3-12

4.0 STATION METADATA AND DATA MANAGEMENT 4.1 Location and Instrumentation The site location of CCUT was described in section 2.0, and a general description of the instrumentation was given in section 3.2. A detailed tabulation of metadata for station CCUT’s location and instrumentation is given in Appendix A (Table A-1). 4.2 Instrument Response Files and Calibration We constructed the response files for both the Streckheisen STS-2 broadband sensor and the REF TEK 131A-02/3 strong-motion sensor using information provided by the manufacturers. All of the information we used for the 131A-02/3 sensor was provided directly by REF TEK. For the STS-2, we used the sensitivity provided in the user’s manual and a pole-zero representation of the transfer function found in links at http://orfeus.knmi.nl. Specific information for both sensors and response files (IRIS SEED Reader, Release 4.6) are given in Appendix A. It is standard UUSS practice to calibrate broadband digital telemetry stations using a step-function method (Pechmann et al., 1999). The software we use for these calibrations, a macro for the Seismic Analysis Code (Goldstein et al., 2003), is available via anonymous FTP to in the file . In this method, the observed and predicted outputs from step function calibration inputs are analyzed to check and revise the manufacturer-supplied instrument response parameters. This simple calibration method appears to work well at periods longer than about onetwentieth of the seismometer free period. However, its absolute accuracy depends on the accuracy of the manufacturer-supplied feedback coil constants, which relate calibration input to acceleration. The feedback coil constants provided with STS-2 seismometers are not sufficiently accurate for use in calibrating the absolute gains of these instruments (Robert Hutt and Joseph M. Steim, written communication, 2005). Therefore, the step function calibration procedure can only be used as a rough check on the response files for the broadband components at CCUT. The broadband channels at CCUT have not yet been calibrated because of a limitation of 300 sec on the spacing of step-function calibration inputs produced by the REF TEK 130-01/6 data logger. A spacing of at least 1200 sec is needed in order to prevent the resulting outputs from the STS-2 seismometer from interfering with each other, given the 120 sec free period of this instrument. Note that we do not use the first step function in a calibration sequence for calibration purposes because of possible interference between the calibration enable signal and the calibration signal itself. The limitation in the spacing of the step function calibration inputs has been reported to REF TEK and a firmware upgrade will soon be available that will allow a longer time interval between such inputs. 4.3 Data Management Data from CCUT (HH[ZEN] and EN[ZEN]) are transmitted from the station site to our UUSS network operations center on the University of Utah campus in Salt Lake City via radio, relay, and Internet as described in section 3.5. At the request of NEIC/USGS we added CCUT HH[ZEN] to the list of stations for which UUSS exchanges continuous data with them via a TCP connection using Earthworm export/import modules. The data streaming to NEIC/USGS began on March 1, 2006. The transfer of continuous waveform data to the IRIS DMC is accomplished through the UUSS Earthworm public waveservers. The IRIS DMC retrieves continuous waveform data from our waveservers several times a day. The continuous waveform data from CCUT are available at the IRIS DMC starting with March 1, 2006. At that time 4-1

we also submitted the metadata (instrument response files) for the CCUT broadband STS-2 waveforms. Essential sensitivity information for the strong-motion triaxial accelerometer was not received from REF TEK until June 28, 2006. The data were then used to build the corresponding instrument response files. Waveform data and the metadata from the triaxial accelerometer at CCUT were submitted to the IRIS DMC on July 5, 2006. The continuous waveforms for these channels are available on the IRIS website, starting with July 1, 2006 (see http://www.iris.edu/servlet/quackquery/budFileSelector.do?station=CCUT&network=UU).

4-2

5.0 PRELIMINARY EVALUATION OF DATA QUALITY 5.1 Noise Analysis of Broadband Data Revisiting the Autumn 2004 noise tests.—In section 2.2 we noted what turned out to be an inconsequential error when we evaluated comparative noise data from two candidate sites for CCUT, the Ox Valley site and the Upper Grants Ranch site, which was ultimately selected. Because we later became aware that an incorrect digitizing constant was used to analyze the Ox Valley data, and also because there was some uncertainty in reconstructing the response file used in the original analysis, we decided to reanalyze those noise data. Once again we used the PDF stand-alone software package of McNamara and Buland (2004), and we consulted with Dan McNamara to verify that our procedures were correct. The revised PDF results are shown in Figure 5-1. Note that the noise data were recorded using a Guralp CMG-40T 30-sec-period seismometer and that at each site the seismometer was placed on bedrock in a shallow hole and simply covered with an inverted foam-insulated water cooler (Fig. 5-2). We make two observations. First, the revised data indicate noise levels about 5–10 dB lower at the Ox Valley site. However, for reasons explained in section 2-2, we still would have selected the Upper Grants Ranch site. Second, the noise tests—at least not with a CMG-40T seismometer installed as we described—do not accurately reflect how good a site can be. To emphasize this point, we next look at noise data recorded after a sensor vault was carefully built at the Upper Grants Ranch site. Preliminary noise data from CCUT.— Seven days of data in SAC format from CCUT HH[ZEN] for the period June 18–25, 2006, were translated to mini-SEED through a series of transformations—from SAC to SEGY to mini-SEED. This dataset was processed with the PDF software and the results are shown in Figure 5-3. The observed noise levels from this preliminary sample of data indicate that CCUT promises to be a high-quality station, with a statistical mode for the power spectral density favorably approaching the low-noise model of Peterson (see McNamara and Buland, 2004). Figure 5-4 is a composite plot that allows comparison of the latest CCUT noise data with (1) Autumn 2004 data recorded at the same site before construction of a sensor vault and (2) data from station SRU, another ANSS/USArray backbone station in Utah of known high quality. The seismic data recorded with the completed vault (Fig. 5-4, middle row) show markedly lower noise levels than the earlier test recording at the same Upper Grants Ranch site (Fig. 5-4, upper row). Noise levels at 10– 100 sec period are ~25 dB lower on the horizontal components and 30–50 dB lower on the vertical component. Although we are comparing “before” data recorded by a CMG-40T sensor with “after” data recorded by an STS-2, the improvement cannot be attributed solely to differences between the sensors. In the lower row of Figure 5-4, the noise data for SRU are from the IRIS Quack system for the month of January 2005 (data are unavailable for 2006). Again, although different broadband sensors are being compared (in January 2005 SRU had a Guralp CMG-3T seismometer), the noise analysis results suggest that CCUT may be at least as good as SRU. 5.2 Example Waveforms from Teleseismic and Local Earthquakes As another way to evaluate the quality of CCUT, we have examined teleseismic and local earthquakes recorded by the station and are very pleased with the data. We first show data from a teleseism of magnitude (MW) 6.2 that occurred in the Aleutian Islands on June 27, 2006 (02:39 UTC), at a distance of 50º from station CCUT. Figure 5-5 shows raw and displacement seismograms recorded by the STS-2 broadband seismometer. Figure 5-6 shows spectra calculated for both the signal and a preevent noise sample. For all three components the signal is clearly above the noise for frequencies from 0.01 to 2 Hz (0.5–100 sec period). 5-1

We next show an example of a local microearthquake recorded by the STS-2 at CCUT. Figure 5-7 shows the raw seismograms for an ML 2.2 event that occurred near Parowan, Utah, on June 26, 2006 (11:02 UTC), at a distance of 72.5 km from CCUT. As shown by this example, the high quality of the recordings is indicative of the station’s value for producing good records of small earthquakes located at significant distances. 5.3 Troubleshooting a “Data Gap” Problem One problem that has caught our attention is a disparity in data gaps between data recorded on our internal systems and corresponding data archived in the IRIS DMC—true not only for data from CCUT but for our other network stations. To illustrate, Figure 5-8 is a plot downloaded from the IRIS Web site showing data gaps per day during the two-month period, May 1–June 30, 2006, for each of the three broadband channels at CCUT. A mean of roughly 10 or more gaps per day is evident for each of the channels. In contrast, a review of our internally archived data for CCUT for this same twomonth period shows 44 days with no gaps and only 1–8 gaps per day per channel on the remaining days. By design, the IRIS DMC retrieves continuous waveforms from a UUSS PC via publicly available Earthworm waveservers. As we add new stations and channels, the PC system can become inadequate in preserving data integrity. Given the great effort and cost invested in making CCUT a high-quality station, we don’t want data quality degraded in the last step of providing data to the user community. We have begun a comprehensive study to determine the cause of this “data gap” problem and will correct it when we have identified the cause.

5-2

Ox Valley

Upper Grants Ranch

Figure 5-1. Comparison of revised PDF noise levels for seismic test data recorded in Autumn 2004 at two candidate sites for station CCUT. The sample data represent continuous recordings of approximately one-week duration at Ox Valley (upper row) and Upper Grants Ranch (below) using a 30-sec-period Guralp CMG-40T seismometer (see Fig. 5-2) and REF TEK digitizer. Data are for the HHE (E-W component), HHN (N-S component) and HHZ (vertical component), respectively.

5-3

Ox Valley

Upper Grants Ranch

Figure 5-2. Photos showing the installation of a Guralp CMG-40T broadband seismometer used to sample continuous seismic data for comparative noise testing in Autumn 2004 at Ox Valley (above) and Upper Grants Ranch (below). In each case, the seismometer was placed on bedrock, consisting of Tertiary porphyritic intrusive rock, in a shallow hole and covered with an inverted foam-insulated water cooler. In the upper row, views are seen before and after covering the seismometer.

5-4

Figure 5-3. PDF noise plots for station CCUT for a seven-day period June 18–25, 2006. STS-2 data are displayed for the HHE (E-W component), HHN (N-S component) and HHZ (vertical component), respectively. 5-5

CCUT (CMG-40T, pre-construction noise testing, 2004)

CCUT (STS-2, final installation, 2006)

SRU (CMG-3T, 2005)

Figure 5-4. Composite figure showing PDF noise plots for three-component broadband data at station CCUT before (upper row) and after (middle row) completion of the station together with corresponding plots for station SRU (see text for details).

5-6

Figure 5-5. Raw and displacement seismograms recorded by the STS-2 broadband seismometer at CCUT from an MW 6.2 earthquake in the Aleutian Islands (Δ = 50º) on June 27, 2006. The displacement traces were obtained by removing the instrument response in the frequency domain and applying a 0.02 to 25 Hz bandpass filter. 5-7

Figure 5-6. Signal (red) and noise (blue) spectra calculated from the raw data in Figure 5-5. A standard FFT was applied to 1000 sec of noise immediately before the P-wave to determine the noise spectra and to 2000 sec of signal immediately after the P-wave onset to determine the signal spectra. The spectra have been smoothed with a moving average window of ± 2 points.

5-8

Figure 5-7. Raw seismograms recorded by the STS-2 broadband seismometer at CCUT for an ML 2.2 local earthquake on June 26, 2006, located 72.5 km away near the town of Parowan, Utah.

5-9

Figure 5-8. Plots of gaps per day, from the IRIS Quack system, for each of the three broadband channels at CCUT for the two-month period May 1–June 30, 2006. Corresponding data internally archived at UUSS contain far fewer gaps (see text).

5-10

6.0 MANAGEMENT DETAILS 6.1 Maintenance and Operation of CCUT Station CCUT is now part of the national backbone network of broadband stations jointly serving the Advanced National Seismic System and NSF’s EarthScope/USArray program. The University of Utah Seismograph Stations (UUSS) has taken the lead in siting and installing CCUT. As stated in our proposal to IRIS submitted May 13, 2005: “UUSS will assume primary responsibility for maintaining CCUT as its associated telemetry links as part of the routine maintenance and operation of its regional seismic network. Because the station effectively will be a new ANSS station, UUSS will seek O&M funding for CCUT under its ANSS cooperative agreement with the USGS.” We plan to maintain and operate CCUT as stated above. 6.2 Title to Equipment Item 7 (Title to Equipment) of the subaward agreement between IRIS and the University of Utah (“Awardee”) states as follows: “Title to all equipment (tangible, nonexpendable, personal property having a useful life of more than one year and an acquisition cost of $5,000 or more per unit) purchased and/or fabricated with funds under this Agreement shall pass directly to the Government from the vendor. The Awardee shall be responsible for control over such equipment in accordance with OMB Circular A-110, “Grants and Agreements with Institutions of Higher Education, Hospitals, and Other Non-profit Organizations,” as revised November 19, 1993, and amended September 30, 1999, until such time as it is delivered to an agent of the Government. Upon expiration or termination of this Agreement, disposition of the equipment will be determined by IRIS in consultation with NSF and the Awardee.” One item of permanent equipment is affected by the above stipulation: (1) REF TEK 6-channel seismic recorder (Model 130-01/6; serial number 9884) with GPS receiver/clock and other accessories; purchased 6/29/2005, acquisition cost = $10,118.24 Pursuant to the last sentence of Item 7 above, we request that IRIS/NSF consider transferring title to this equipment item to the University of Utah. Given that CCUT is a permanent station for which neither IRIS nor NSF intends to bear any responsibility for repair and maintenance, retaining title to this one equipment item seems impractical. Otherwise, we assume that IRIS/NSF will be responsible for repair costs if the seismic recorder fails after its warranty period. 6.3 Data Availability As an ANSS-funded regional seismic network, UUSS is required to adhere to the “Advanced National Seismic System Elements of Data Policy” adopted by the ANSS National Implementation Committee in December 2003. Under that policy, all digitally-recorded waveforms from stations we maintain and operate are archived at the IRIS DMC. (Data are also transmitted continuously to the USGS/NEIC; see section 4.3). Availability of data from CCUT as a national backbone station is assured. 6-1

7.0 REFERENCES McNamara, D. E., and R. P. Buland (2004). Ambient noise levels in the continental Unites States, Bull. Seism. Soc. Am. 94, 1517—1527. Pechmann, J. C., S. J. Nava, and W. J. Arabasz (1999). Installation and calibration of five new broadband digital telemetry stations in Utah, Seism. Res. Letters 70, 244. Goldstein, P., D. Dodge, and M. Firpo (2003). SAC2000: Signal processing and analysis tools for seismologists and engineers, in International Handbook of Earthquake and Engineering Seismology, Part B, W. H. K. Lee, H. Kanamori, P. C. Jennings, and C. Kisslinger (Editors), 1613-1614.

7-1

APPENDIX A METADATA AND RESPONSE FILES FOR STATION CCUT Key to Channel Response Labels in SEED Format HHZ

H (High broadband)

H (High-gain seismometer)

Z (Vertical-component)

HHE

H (High broadband)

H (High-gain seismometer)

E (East-West component)

HHN

H (High broadband)

H (High-gain seismometer)

N (North-South component)

ENZ

E (Extremely short period)

N (Accelerometer)

Z (Vertical-component)

ENE

E (Extremely short period)

N (Accelerometer)

E (East-West component)

ENN

E (Extremely short period)

N (Accelerometer)

N (North-South component)

A-1

Table A-1 Metadata for Station CCUT—Location and Instrumentation

Location Information Latitude: Longitude: Elevation:

37° 33.040′ North 113° 21.765′ West 2124 m

UTM North: 4158586.3 UTM East: 291282.2

Instrumentation •

REF TEK 6-channel, 24-bit digital seismic recorder (Model 130-01/6; S/N 9884) with GPS receiver/clock and 1 GB flash memory

•

Streckheisen triaxial broadband seismometer (Model STS-2; S/N 80223)

•

Applied MEMS, Inc., triaxial micro-electro-mechanical system (MEMS) force-balance accelerometer (REF TEK Model 131A-02/3; S/N 00081) with ±3.5g full scale

Digitizer Channel No.

Component

Sensor Model

Serial Number

Sensitivity

1 2 3 4 5 6

Z E N Z N E

STS-2 STS-2 STS-2 Applied MEMS Applied MEMS Applied MEMS

80223 80223 80223 00081 00081 00081

1500 V/m/s 1500 V/m/s 1500 V/m/s 2.462 V/g 2.454 V/g 2.416 V/g

A-2

A-3

A-4

A-5

A-6

A-7

A-8