ISSN 07479239, Seismic Instruments, 2014, Vol. 50, No. 3, pp. 206–220. © Allerton Press, Inc., 2014. Original Russian Text © A.V. Danilov, G.N. Antonovskaya, Y.V. Konechnaya, 2013, published in Seismicheskie Pribory, 2013, vol. 49, no. 3, pp. 5–24.
Specific Features of Seismic Station Installation in the Arctic Region of Russia A. V. Danilova, G. N. Antonovskayaa, and Y. V. Konechnayaa, b a
Institute of Environmental Problems of the North, Ural Branch, Russian Academy of Sciences, Arkhangelsk, Russia email:
[email protected];
[email protected] b Geophysical Survey, Russian Academy of Sciences, Obninsk, Russia email:
[email protected] Abstract—The methodological and technical guidelines for setting up seismic event recording stations in Russia’s Far North are presented. The main types of recommended seismic instruments and dataacquisition and transmission methods are discussed. Keywords: seismology, Arctic Region of Russia, seismic instruments, principles and methods for setting up seismic stations, seismic data transmission DOI: 10.3103/S0747923914030037
INTRODUCTION In connection with planned intensification of industrial development of the Russia’s Arctic region, primarily, the mining, manufacturing, and transporta tion industries, safe functioning of the corresponding enterprises has become a line of research. Safety mea sures are provided for all phases of an industrial project’s lifetime: design, construction, and opera tion. The current OSR97 general seismicriskzoning map used to check the engineering projects under development for potential seismic impacts (SNiP II781*..., 2007) as applied to the northern ter ritories including the Arctic region, does not reflect the uptodate level of knowledge on the seismic con ditions and requires updating. In particular, as moni toring results show, the shelf areas of the EuroArctic region display noticeable seismic activity not embod ied in OSR97 maps. In this connection, a survey is extremely urgent to more more precisely evaluate the seismicity of the Arctic and Subarctic territories. The OSR97 maps are based on a probabilistic approach to temporal and spatial origination of foci of earthquakes with different magnitudes (Ulomov, 2009; 2012). However, owing to the fact that seismological investigations of the Russian Far North territories have not received adequate attention, the information on the seismicgeodynamic processes in this region is not comprehensive. At present, Russia is falling consider ably behind its Arctic neighbors Norway, Denmark, and Canada in investigating the seismicity of the region. The network of seismic stations in the Russian Far North is sparse and nonuniformly distributed, partly due to a number of objective factors: a low degree of
planning and management of land use, poorly deveóloped road networks in combination with natu ral, climatic, and permafrost conditions of the Far North, etc. All this restricts the choice of sites suitable for setting up seismic stations and corresponding infrastructure. Moreover, until recently, the platform regions have been considered aseismic, i.e., those not on the list of observation priorities. Until 1960, information on earthquakes in the Arc tic region came from seismic stations located in Rus sia’s midlatitudes; they could provide data only on severe earthquakes. A major breakthrough in studying of the seismicity of the Arctic was achieved in the 1957– 1958 International Geophysical Year. The network of analog seismic stations created by 1960 north of the Arctic Circle reliably recorded arctic earthquakes with magnitudes of M = 4.5 and above and, for some regions, weaker events with M = 4 (Assinovskaya, 1994). By the late 1980s, 43 seismic stations were operating in the Arc tic region, 22 of which were located in the western and 21 in the eastern parts of the Arctic (Avetisov, 1996). After the collapse of the Soviet Union, only sta tions of the Kola Peninsula seismic network were able to continue operating; this network, integrated into the Geophysical Survey of the Russian Academy of Sciences, is predominantly engaged in seismic moni toring of the western part of the Arctic region (Asming, Kremenetskaya, and Ringdal, 1998; Vinogradov et al., 2012). Since there have been hardly any seismic sta tions over the entire period of development of Russian seismic stations, the eastern part of the region has been underexplored. Only since 2004, when a regional net work began to be developed “from nothing” in Arkhangelsk oblast, systematic acquisition of seismic information began (Seismologicheskie…, 2011). A fun
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damental contribution to this work was made by F.N. Yudakhin, Corresponding Member, Russian Academy of Sciences, and V.I. Frantsuzova, Cand. Sci. (Phys.– Math.). When positioning the Arkhangelsk regional net work, the developers faced an absence of norms or rec ommendations for placing seismic station networks starting from the installation of individual stations to seismic station groups. Presently, there are no engi neering regulations on seismic station equipment or the testing of modern instruments designed for seis mological monitoring (Mishatkin and Zakharchenko, 2010) that could be compared to the manual (Appa ratura..., 1974). Special normative documents for positioning of which are engaged in solving particular problems, e.g., provision and safe operation of critical facilities within their competence, including those located in the high seismic activity zones (STO 70238424.27.140.032– 2009, STO 95.103–2013). A characteristic feature of these documents is recommendations on the structure and instrument completion of the monitoring systems. These documents contain general information but do not deal with engineering issues. As an example, we consider a number of problems to be dealt with: at what depth should the foundation of a seismic station be constructed and what height it should be; how should the parameters depend on ground type; which type of structures—castinplace, prefabricated, etc.—can be used when laying the foundation; the grade of cement; permissibility of reinforced struc tures; and what the seismic structure (underground shelter) should be, as well as its allowable dimensions are. Under certain circumstances, these questions can be difficult for even an experienced seismologist to answer. Even greater difficulties arose when the seismic sta tions were installed north of the Arctic Circle. The researchers of the seismological laboratory of the Institute of Environmental Problems of the North, Ural branch, Russian Academy of Sciences, resumed operating the seismic event recording station in the settlement of Amderma in 2010. The real situation in the area showed that there was no possibility of install ing sensors where they had been installed previously, in a coal mine (Vinogradov et al., 2012). At present, the seismic station is at the edge of the settlement, on the territory of a weather station in a deserted basement; however, engineering problems concerned with checking the equipment and the data transmission techniques had to be solved. In 2011, seismic stations in NaryanMar and in Franz Josef Land were launched. Today, three sets of seismic instrumentation have been installed on Alexandra Land of the Franz Josef Land archipelago (Antonovskaya, Konechnaya, and Morozov, 2013). This activity made it possible to pool the experi ence of installing seismic event recording stations; the concept of placing such stations under Far North con SEISMIC INSTRUMENTS
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ditions was developed, including acquisition and transmission of seismic information. We hope that this experience will be helpful for institutes engaged in ensuring seismic safety of Far North territories and allow them to avoid many unfor tunate mistakes in the future, because every error in severe Arctic conditions are, in economic and engi neering terms, much more difficult to correct than in other regions located further south. SEISMIC INSTRUMENTATION The seismic instrumentation to be installed in seis mic event recording stations in the Arctic region has to meet the following requirements: —reliable operation at low temperatures (to – 35°C) and high humidity (relative air humidity 80– 90%); —transportability; —manufacturability and serviceability (possibility of training personnel with no special knowledge); —backup storage on the sensor’s or recorder’s internal data medium; —availability of backup power; —low power consumption; —remote control (adjustment, restart, reports on sensor state, and uploading of data from internal data medium). Tables 1 and 2 show information on the sensors and recorders used in practice and evaluation of usability of the instrumentation under Far North conditions. Sensors and recorders produced by the companies Kinematrics and Nanometrics are the most robust and widely used by the world seismic community in north ern regions. Less widely used are instruments pro duced by Guralp Systems Ltd. Among domestic man ufacturers of instrumentation designed for the Far North and successfully tested us, noteworth are the RSensors Company, which develops only veloci meters, accelerometers, and torsion oscillation sen sors, and OOO AlexLab, which has developed the KBS1…3 recorder series; among its latest develop ments is the ADSR3 station (Udalennyi …, 2013). Only Guralp Systems Ltd.—NPP VULKAN— has an official representative in Russia; therefore, most seismic station networks in Russia are equipped with instruments produced by this company. The Arkhangelsk network is no exception; there, the seis mic stations are equipped predominantly with three component wideband CMG3ESP and CMG6TD velocimeters. The CMG6TD velocimeter is com bined sensor and recorder. It has proven to be a multi purpose tool for solving both fundamental and applied problems. Let us consider in detail the CMG6TD sensor and its basic technical characteristics established during its operation under Far North conditions.
SEISMIC INSTRUMENTS
3
3
Velocimeter CMG3ESP
Velocimeter CMG6T
3
3
Accelerometer CMG5T
Velocimeter CMG40T
1
2
1
Velocimeter SM3KV
Number of components
Sensor
Table 1. Seismic equipment
Analog/digital
Analog/digital
Analog/digital
Analog/digital
Analog
3
Type of output signal
0.03–50
0.03–100
0.008–50 0.03–50
0–100
0.5–100
4
Frequency band, Hz
–20 ... +75
–40 ... –75/ –20 ... +85
–20 ...+65
–20 ... +70
–10 ... +40
5
2.5
2.5/2.7
9.3/8.3
2.7/4.3
8
6
+
+
–
+
–
7
Operation Usability temperature Weight, kg (+/–) range, °C
Great Britain (Guralp..., 2013)
Russia (SM3KV..., 2013)
8
Manufacturer
Recording of seismic events of various types
Recording of seismic events of various types. Sensitive to transporta tion and temperature dif ferences
Recording of seismic events of various types
Recording of local and regional events. Sen sitive to transportation
9
Remark
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3 linear and 3 torsion
6channel bottom sensor CME 206CWP10
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Analog
Analog
Analog
Analog
3
3
3
3
3
3
Velocimeter Trillium Compact
Velocimeter Trillium 120
Downhole velocimeter Trillium PH
Velocimeter Trillium 240
Velocimeter STS2.5
Downhole velocimeter STS5A
Analog
Analog
3
Analog
Analog
Analog, differential
3
Type of output signal
METR03LT torsion oscillation sensor
3
2
1
Velocimeter CME4211
Number of components
Sensor
Table 1. (Contd.)
0.008–50
0.008–50
0.004–200
0.008–150
0.008–145
0.008–100
0.05–20
0.033–50
1–300 linear 0.03–100 torsion
4
Frequency band, Hz
–20 ... +70
–20 ... +70
–20 ... +50
–40 ... +55
–20 ... +50
–40 ... +60
–12 ... +55
12
14
16
7.5
1.2
1
4.9
5
–40 ... +50
–12 ... +55
6
5
+
+
+
+
+
+
+
+
–
7
Operation Usability temperature Weight, kg (+/–) range, °C
USA (Kinemetrics..., 2013)
Canada (Nanometrics..., 2013)
Russia (RSensors..., 2013)
8
Manufacturer
Recording of seismic events of various types
For engineering problems
Recording of seismic events of various types
Recording of local and regional events. Light weight. Requires improvements according to the seismic survey needs
9
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Number of recording channels
24 24
3
12, 24, 36
6
Basalt 4X Basalt 8X
Q330HR
The Taurus Digital Seismograph Granite
4 8
5
Power consumption
6
Ethernet/Wi Fi/
Options +
+
Flash
+
– +
12 channels: 335 mA = 4.02 W
127 dB at 200 counts/s; 130 dB at 100 counts/s
145 mA = 1.74 W 230 mA = 2.76 W
6 channels: 208 mA = 2.5 W
62.5 mA = 0.75 W
+
+
+
+
2.5
4
0.5 0.5
8
Weight , kg
–40 ... +60
1.8
–20 ... +70
–20 ... +70 4.6 7.3
7.3 –20 ... +70 (12 chan nels ) 3.6
–20 ... +60
7.2
2
2 (4 chan –30 ...+50 nels)
–20 ... +40
–20 ... +55
–40 ... +75
–20 ... +40
7
Operating temperature range, °C
Flash –40 ... +80 carrier 140 mA = 1.68 W Flash –20 ... +70 carrier
4 channels: 67 mA = 0.8 W, 32 channels: 417 mA = 5 W 3 channels: 77 mA = 0.92 W; 6 channels: 120 mA = 1.44 W 2W
58 mA = 7 W
129 dB at 100 counts/s; 133 dB at 50 counts/s >141 dB at 100 counts/s
135 dB at 100 counts/s
137 dB at 100 counts/s; 141 dB at 40 counts/s
124 dB at 50 counts/s; 120 dB at 250 counts/s
144.5 dB
120 mA = 1.44 W 108 dB at 100 counts/s 130 dB at 200 counts/s; 160 mA = 1.92 W 142–144 dB in band 20 Hz To 6 W 120 dB
4
Dynamic range
144–145 dB 3 HR 26bit and 3 standard 24bit 127 dB at 200 counts/s; 24 130 dB at 100 counts/s
24
24
32
24
16
24
31
22
3
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3
3, 6, 9, 12
432
3
2–4–6– ... ⎯24 or 3–6– 9–...–24
3
3
2
ADC digital capacity
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GSR24
Baikal
CMGDM24
ZET 048I
UGRA
DIOGENX/24S
ADSR3
KBS3
1
Model
Table 2. Recorders
9
Usability at fixed stations (+/–) +
+
+
+
+
–
+
–
–
+
– +
USA (Kinemetrics..., 2013)
Russia (RSensors..., 2013) Switzerland (Recorders..., 2013) Canada (Nanometrics..., 2013)
Great Britain (Guralp..., 2013)
(Mekhryushev, 2007) Russia (ZET048I..., 2013)
Russia
Russia (Diogen..., 2013)
Russia Russia
10
Manufacturing country
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The major advantages of this instrument, as com pared with its counterparts, include: a lightweight sen sor, which is a combined velocimeter and recorder; a robust waterproof anodized aluminum housing; ease of assembly and start (horizontal deviation toler ance 3°; when connected to the power source, data recording starts almost immediately); operability in various data recording modes, including internal flash memory; a wide frequency range of recorded signals; high sensitivity; low power consumption; and remote control of the equipment. All this justifies its preferen tial use in field investigations in a wide range of weather conditions and geophysical problems. The CMG6TD sensor is equipped with a GPS antenna; the GPS module itself is located inside the sensor. Without the GPS antenna, the current data and exact time can be reset by the instrument at a default value. This can result from a fault in the GPS module, like when dogs bit the GPScable in one of the instrument kits of the Franz Josef Land seismic station. Such events are a harsh reality: animals in the Far North, such as polar bears, dogs, birds, etc., are a real threat to reliable recording. The fault could be repaired only in summer: they had to break into the underground shelter, remove the sensor, and restore the settings. As a result, the seismic data acquired over more than two months was lost. Consequently, the GPS cables must always be protected. Another drawback of the CMG6TD sensor is that the pendulums are not arrested, i.e., the moving sensi tive part of the working parts is not mounted on mechanical stoppers when the instrument is trans ported and/or stored. The manufacturer advises that such a procedure is not required and it suffices merely to handle the instrument carefully. However, owing to specific conditions when delivering equipment in the Far North, especially by air, helicopter, and offroad vehicles, even when handled carefully, the sensors can deviate from a zero setting. In such a case, one has to reset them to a zero setting manually, which can dam age the instrument’s pendulum when the housing is removed or mounted. The next disadvantage of the CMG6TD sensor is unreliable operation of the internal software. For example, data may not be uploaded from the sensor’s internal memory directly to computer owing to certain errors in the sensor’s microprogram. In addition, sometimes the sensors spontaneously restart and the adjusted settings are completely reset to the default settings; the latter has occurred only twice in two years of operation. In all probability, these problems are also related to the instrument software. Such a decrease in reliability, which is insignificant when there is a per manent operator, may cause irreparable data loss when a specialist cannot get to the sensor immediately. SEISMIC INSTRUMENTS
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SELECTION OF WHERE TO INTSALL A SEISMC EVEN RECORDING STATION When selecting the place to install the seismic event recording station, depending on the geology and the geophysical structure of the area, one should be guided by the following requirements: —The area where a new station is to be installed must sufficiently significance for geodynamic investi gation of the territory and complement the existing seismic station network in the best way. —It is necessary to take into consideration the seismic characteristics of the ground (the ground of categories I or II is preferable). Rocky ground is opti mal, but any other dense types of ground like marl or limestone are also suitable. Areas with the occurrence of heavy claysand layers should be avoided. When the sensors are installed on ice, the temperature in the vicinity of the sensor should be stabilized in order to prevent melting of ice and deviation of the sensor level from the horizontal position. —It should be possible to either construct a seis mic underground shelter for the sensor or install the sensor without any shelter but with protection from weather impacts such as fluctuations in pressure, tem perature, and humidity, as well as from unauthorized access. —Accessibility of the place of installation to the transport. —The place for the station must be maximally insulated from the external oscillation sources (a low level of natural microseisms and manmade vibra tions). —Possibility of laying out cables—a 12, 24 or 220V power cable and/or a signal wire—from the computer to the recording devices. —The server/computer should be in a room where the temperature does not fall below 0°C. —Possibility of online data transmission, trans mission in a nearrealtime mode or in any other accessible mode. As a rule, a several most suitable—in terms of external and geological conditions—places should be chosen where the microseismic background is ana lyzed and, according to this, the most suitable place for installation is selected (Yudakhin, Kapustyan, and Antonovskaya, 2007). CONSTRUCTION OF A SEISMIC UNDERGROUND SHELTER Installations designed for seismic survey should meet the following requirements: —appropriate conditions should be ensured for equipment operation, e.g., pressure, thermo, and hydraulic insulation; —proper mechanical contact between seismome ters and the underlying rock;
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mines, but one should consider potential exogenous natural microseisms associated with the internal stresses of the environment, such as noise in salt beds, stress relief in mine workings, etc. (see (Kapustyan and Yudakhin, 2007)). If the conditions do not enable proper burying, for example, in the presence of a rocky ground, the sensor should be placed on a ground sur face provided with appropriate protection. Under per mafrost conditions and in the absence of specialized heavyduty construction equipment, digging a pit for a seismic structure becomes extremely complicated. Based on their experience, the authors can say that a petrol rock breaker considerably simplifies the task (Jackhammers..., 2013). With scant financing, 200L metal fuel and lubri cant barrels (Fig. 1) widely available at the site can be employed to equip seismic stations in the Far North.
Fig. 1. Barrels used as the base for a seismic underground shelter.
—reduction in noise caused by exogenous natural processes and manmade noise; —a preset stable temperature and humidity values in the operational ranges; —shielding and protection from lightning, grounding of the seismic equipment; —vandalproofing and prevention from rain, snow, dust, dirt, mould, insects, and animals. In order to reduce the level of ground noise from manmade and exogenous natural microseisms, the seismometers should be buried; the deeper the seismic facility, the better. A good option is decommissioned (a)
A barrel is cut into two parts 20 cm below the upper edge. The height of the larger part of the barrel allows all necessary manipulations with equipment, namely, to easily place the sensor at the bottom of the barrel and position it horizontally using a bubble level. Along the circumference of the both barrel parts, 5–7cm deep cuts should be made to connect them more easily afterwards. First, a pit for the barrel is dug. Judging from the authors’ experience, the optimal depth of the pit, tak ing into consideration the barrel’s dimensions, is 60– 70 cm. A foundation of a cement–sand mixture is made at the bottom of the barrel, onto which the barrel is mounted before it has completely cured. The cement should be of M400 grade at least; at a temper ature below 5°C, a lowtemperature accelerator should be added. After the cement has cured—about 24 h later—the pit is filled with earth and rammed (Fig. 2a). The barrel should protrude 10–15 cm over the ground level. (b)
Fig. 2. (a) Preparation of the base and (b) placing of the barrel. SEISMIC INSTRUMENTS
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(b)
Fig. 3. Construction of a seismic underground shelter.
Then, the barrel has to be coldproofed. As a heat saving material, pieces of foam polystyrene can be used, which are laid out as shown in Fig. 2b. The pieces are toroidal in shape; their minimum number is determined by the height of the sensor. In the middle of the piece, an opening is cut out equal to the sensor diameter with an additional 10–15 cm to enable level ing of the sensor. In addition, solid pieces (without a central opening) of the heatsaving material are made, one of which, provided with a small hole for cables from the sensor to the computer, is glued to the inter nal surface of the smaller part of the barrel, which serves as the cover. After mounting the equipment and laying out the cables, the vacant space inside the barrel is filled up with the heatsaving material and the barrel is closed (Fig. 3a). All gaps between the cover and the lower part of the barrel have to be sealed with a waterproof sealant or a reinforced tape. After all these procedures are completed, the barrel is covered with earth (Fig. 3b). DATA TRANSMISSION A seismic signal can be transmitted from the sensor to the receiving computer via copper wires, optical fiber, or wireless communication channels. For data transmission, standard communication tools offered by instrument manufacturers are used; for CMG6TD velocimeters, these are EIA232 (RS232) interfaces. However, when the data are transmitted over distances larger than those enabled by a standard interface, auxil iary builtin interfaces can be used. Depending on the sensor bundling, it can be WIFI and/or Ethernet inter SEISMIC INSTRUMENTS
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faces or some auxiliary external devices (signal convert ers (Tables 3 and 4)). Over short distances to 20 m, an EIA232 (RS232) interface can be used; over distances to 100 m, an Ethernet 100BASET interface; and for distances over 100 m, specialpurpose converters are used, which are presented in Table 3. The most convenient and economically effective signal transmission medium is a radio signal. How ever, in case of any faulty operations or a loud noise, for example, thunderstorm static, the wireless data transmission module integrated into the sensor is dis connected. Its restart and resetting is possible only if it is connected to a standard EIA232 (RS232) inter face. To prevent this, a standard EIA232 (RS232) interface should be employed, which, when transmit ting data for a distance over 20 m, is converted into either a WIFI radio channel or an EIA485 (RS 485) or EIA422 (RS422) interface. Analysis of Table 3 shows that the EIA485 (RS 485) or EIA422 (RS422) interfaces are the most suitable for data transmission in arctic conditions. Their major difference is that the EIA422 (RS422) interfaces are always duplex with four conductors and the EIA485 (RS485) interfaces can be both semidu plex with two conductors and duplex with four con ductors. The EIA485 (RS485) interface ensures a multipoint structure and enables connection of several receivers–transmitters to one line, unlike the EIA 422 (RS422) interface, which enables only one receiver–transmitter and several receivers in the line. As a rule, converters that combine interfaces of both types are manufactured. Reasoning from the above, the authors selected the EIA485 (RS485)
SEISMIC INSTRUMENTS
WiFi radio channel
Optical fiber
EIA422 (RS422)
EIA485 (RS485)
Data transmission device
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Antenna DLink ANT242100
To 10000
To 2000
Antenna DLink ANT240800
2500
Advantech ADAM4541 (multimode optical fiber) To 3000
5000
Korenix JetCon 2401m (multimode optical fiber)
Antenna HiTE WiFi19
40000
+
+
+
+
+
+
+
Advantech ADAM4522
MOXA TCF142SSTT (monomode optical fiber)
+
+
Korenix JetCon 220 liw
1200
–
ICP DAS I7520AR
MOXA TCC100I
+
NIL AP NL232C
+ –
1200
–/283
–/103
–/112
–/214
–/138
–/428
+/71
+/100
+/121
+/70
+/95
+/55
+/121
Data transmission Possibility of duplex Ease of assembly/ distance in one line data transmission cost (USD) segment, m
OVEN AS3M
MOXA TCC100I
Signal converter
Table 3. Data transmission options using the EIA232 (RS232) interface
–40...+70
–40...+80
–30...+70
–10...+70
–20...+70
–40...+75
–10...+70
–40...+70
–20...+60
–25...+75
–40...+70
–20...+75
–20...+60
Operating temperature range, °C
(WiFi..., 2013)
(WiFi..., 2013)
(InSAT..., 2013)
Source
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Table 4. Types of signal converters connected to the computer Data transmission device
Signal transformation
EIA485 (RS485) interface In the USB
EIA485 (RS485)interface In the Ethernet
Optical fiber
Signal converter OVEN AS4
–
+/59
MOXA UPort 1150
+
+/89
Kron TUSB485 GS V12
–
+/70
Advantech ADAM4571
+
+/179
VSCom NetCom 113 Din Rail
+
+/127
MOXA NPort 5130
+
+/135
Advantech EKI2541MAE (multimode optical fiber)
+
–/156
MOXA IMC21MSC (multimode optical fiber)
+
–/182
MOXA IMC21SSC (monomode optical fiber)
+
–/271
Korenix JetCon 1301m (multimode optical fiber)
+
–/88
Korenix JetCon 1301s (monomode optical fiber)
+
–/138
interface and employed it in one of the instrument sets in the FJL seismic station for data transmission within a distance of 1000 m. The signal from the sensor is converted from the EIA232 (RS232) into the EIA 485 (RS485) interface. Afterwards, the EIA 485 (RS485) interface has to be converted to be con nected to the computer. To adapt to the computer’s standard interfaces, interface converters or media converters are used, the main types of which are pre sented in Table 4 (InSAT..., 2013). The data are transmitted from the sensors to the computer via specialpurpose software. Thus, when using the Guralp instrumentation, the Scream! seis mic monitoring software is used to compose files with seismic records and visualize them on the computer (Guralp…, 2013). Depending on the geology and the remoteness of the area where a seismic station is installed, infrastruc ture availability, and other conditions, the mounting of radioantenna supports may be significantly compli cated. Moreover, the quality of the transmission signal is affected by the weather conditions, which can cause intermittent communication and the data may get lost. Unlike wireless channels, cable lines ensure stable signal transmission. Owing to the technical infeasibil ity of laying out/connecting optical fiber under Far North conditions, e.g., the need to engage specialized companies and lack of financing, preference was given SEISMIC INSTRUMENTS
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Duplex Ease of assembly/ data transmission Price (USD)
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to copper wires, since this could be done without out side assistance. When selecting the data transmission cable, atten tion should be paid to the following: —availability of an armored covering as a protec tion against mechanical damage; —shielding to prevent impact of external fields on the signal; —availability of polyethylene insulation, which ensures good insulating properties; low dielectric losses; light weight and smaller dimensions of the cable as a whole, which facilitates its layingout in both cable work and in the ground in complicated cable trenches; high moisture resistance; a smaller bending radius; and the possibility of laying the cable in trenches with an unlimited difference of levels. Table 5 shows the main types of cables that meet the above requirements. The choice of the conductor cross section and number of conductor pairs depends on the problems to be solved. For example, for a volt age of 24 V and a transmission distance of 1 km, the optimal conductor cross section is at least 1.5 mm2. The P270 cable meets all the above requirements in the best way; therefore, the authors chose this type of cable to be laid out on Alexandra Land in the Franz Josef Land archipelago. Depending on the conditions where the seismic station is installed, the cable is laid out over the earth surface, in the ground, or strung between special poles. In some cases, when the cables
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Fig. 4. Laying out of cables for a seismic station in a metal tube.
need additional protection, e.g., in places where cer tain means of transport run, they are laid out in tubes of the required diameter (Fig. 4). So that they will not be chewed up by animals, cables are also laid out in tubes or metal corrugation, or lubricated with some chemical compound, e.g., lithium grease. The data can be transmitted to the data processing center via satellite communication, the Internet, or by mail, depending on the infrastructure available in the area where the equipment is installed. If no communi cation means are available, the operator copies the data to a portable data medium and sends it to the data center via any available means. For example, in the Kola branch of the Geophysical Survey, Russian Academy of Sciences, the data from sensors of the Apatity seismic station group are transmitted to the data center in Apatity via rf modems. There, these data are supplemented with data from the Apatity long period seismic station; the information is integrated into secondary blocks and recorded in a circular disk buffer. In the circular disk buffer, the data are stored for 14 days and then replaced by updated information. During this period, an automatic event detector (EL software package) browses through the data, which selects the record fragments that correspond to real seismic events, stores them in the form of CSS files, and locates them (Seismic..., 2013). The Iridium OpenPort satellite communication system is the most stable in the Arctic regions of Rus sia; its main drawback is its very high price (Satellite…, 2013). The data are transmitted via the Internet either using specialpurpose equipment and software from the provider, e.g., 3G modems, or via standard com puter soft and hardware. The data can be transmitted to the data processing center both in the online mode and in the nearrealtime mode in the form of the files, depending on the capacity of the Internet channel.
INSTALLATION AND ADJUSTMENT OF SEISMIC INSTRUMENTATION As shown above, to perform the seismic survey, the sensor (a velocimeter/accelerometer) is placed in a specially prepared barrel at the seismic station. When an analog sensor and a recorder are used, the latter is installed at the top of the barrel over the sensor between the heatsaving material layers (Fig. 5). Then, the barrel is densely closed with a cover and com pletely buried in the ground. The GPS antenna is fixed to a mast (pole) near the station. The necessary software bundled, as a rule, with the sensor, is installed on the receiving computer. An operation mode is selected in the sensor, in which the data are automatically sent to the computer and the sensor’s internal flashmemory if possible. Afterwards, the data are forwarded to the data processing center via any available means. ELECTRIC POWER SUPPLY FOR SEISMIC EVENT RECORDING STATIONS To set up a seismic event recording station, an electric power supply is essential. To date, there exist a great num ber of independent power supply sources. The most widely used systems are based on (Types…, 2013: —diesel or petrol generators directly connected to 220V power grids; —wind power generators; —solar cell panels; —automated complexes that comprise an inverter, electric batteries, and a generator; —inverters or uninterruptible power supplies (UPSs) fitted with rechargeable batteries. The advantages of systems that use generators are their low cost and complete independence from exter SEISMIC INSTRUMENTS
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Fig. 5. Installation of a velocimeter in the prepared underground shelter.
nal power grids. Their drawbacks are a high noise level, short lifetime, and difficult maintenance. Alternative power sources, such as wind power gen erators and solar cell panels, are completely indepen dent and do not involve any fuel costs. Their disadvan tages include high cost, dependence on weather con ditions, necessity of safeguarding measures in some cases, and complicated assembly. Systems based on inverters or UPS equipped with accumulator batteries have the following advantages: —almost instantaneous switchingon of the stand by power supply without any interruption in the case of a sudden power outage; —installation in any place, even in a living area or unventilated space; —the absence of noise and exhaust gases; —they do not require constant control and fre quent servicing and have a long lifetime; —they consume power in the most efficient way depending on load; —reasonable cost. Among the disadvantages of such systems are a lim ited operation time, which depends on the battery capacity: in standby mode, the batteries have to be constantly recharged from the power grid, which results in extra power consumption, and impossibility for the inverters to operate for a lengthy period of time for high load and power values. To avoid such problems, systems based on an auto mated complex comprising an inverter, rechargeable batteries, and a generator are used. The generator is automatically switched on upon battery discharge, ensuring simultaneous power supply and battery charging, which considerably reduces fuel consump tion and enables the creation of a completely indepen dent power supply system. SEISMIC INSTRUMENTS
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The selection of a particular power supply system is determined by the problems to be solved, available finances, and the conditions in the area where the seis mic event recording station is installed. In the authors’ opinion, the system based on an automated complex comprising an inverter, rechargeable batteries, and a generator is the most economically sound solution for the conditions of the Far North. EXAMPLES OF SEISMIC EVENT RECORDINGS The difficulty in installing the seismic event recording stations in the Arctic is compensated by the possibility of obtaining data unique for the present time. The opening of the seismic event recording sta tion in the Franz Josef Land archipelago enabled recording of events with M = 1.9 that occurred in the Arctic region. In particular, the results of the constant survey carried out from September 2011 until December 2012 yielded new data on the seismicity on the boundary of the continental shelf (Fig. 6). Most recorded events refer to the slope of the oce anic shelf in the vicinity of the FranzVictoria Trench. To date, it is impossible to define focal earthquake mechanisms owing to the small number of stations that surround and record earthquake foci. The seismic activity in the area of the FranzVictoria Trench, unlike the St. Anna Trench west of the Franz Josef Land archipelago, is a natural phenomenon according to G.P. Avetisov (Avetisov, 1996) if the Svalbard Uplift is considered a uniform block responsible for the seismic process. Thus, the results confirm the seismic activity in the area of the FranzVictoria Trench and allow us to draw preliminary conclusions about specific features of the seismic conditions on the continental slope of Eurasia within the boundaries of the Franz Josef Land archi
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CONCLUSIONS
80°
Franz Josef Land
KBS SPITS N E
75°
W
1 10°
S
2 20°
30°
40°
Fig. 6. Map of sources of earthquakes recorded by the Franz Josef Land seismic station in the area of the conti nental shelf from September 2011 until February 2013. (1) Earthquake sources; (2) seismic station.
pelago, thereby stressing the uniqueness and signifi cance of the Franz Josef Land seismic event recording station for investigating the seismicity of the Arctic. Since the opening of the Amderma seismic event recording station in November 2010, the flow of recorded manmade events has increased, which allowed us to improve the methods for defining the nature of the recorded events (Fig. 7).
This work summarizes information on the types of seismic equipment, the selection of where to install seismic event recording stations, construction of underground shelters, techniques for data transmis sion, installation and adjustment of seismic instru mentation, and ways to ensure electric power supply for seismic stations. This enable one to select the most optimal options and equipment depending on the place where the station is installed and the available infrastructure. The work does not claim to provide comprehensive coverage of all variants for installing the seismic event recording stations in the Arctic region of Russia. We hope that our experience and the information we pro vide will be helpful to our colleagues and seismologists and allow them to avoid many engineering problems they may face when installing the equipment. ACKNOWLEDGMENTS The proposed materials are based on data collected when performing works aimed at expanding the Arkhangelsk seismic station network, supported by the “Human Resources in Science and Education for Innovative Russia for 2009–2013”; the Federal Target Program, contract no. 14.740.11.0195 and agreement no. 8331; the Russian Foundation for Basic Research, projects no. 100500497 and 110598800r_sever_a; by the Presidium of the Russian Academy of Sciences, program nos. 09P51019 and 12P51009; and by a grant from the President of the Russian Federation, project no. MK6178.2012.5.
55°
60°
65°
72°
70°
AMD
68° Vorkuta
Fig. 7. An example of the manmade event recorded by the Amderma seismic event recording station (denoted as AMD) in the opencast mine of the Vorkuta mining complex. SEISMIC INSTRUMENTS
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2.4 ... 144 2.4 ... 48 2.4 ... 48 8.10 ... 48 8.10 ... 48
OKBT
OKBs
OM3KGTs
OM3KGM
2/0.86
P296
OKBP
3/2
P269
1.2 ... 12
2/9.2
P270
Gerda KOUTK
2/1.5
2/1.5
2/1.5
Number of conductor (optical fiber) pairs/ conductor cross section, mm2
Gerda KUIN
Gerda KVIP
Gerda KPsK
Cable marking
Table 5. Types of cables and their characteristics
+
+
+
+
+
+
–/+
–/+
+/+
+/+
+/+
+/+
Armor/screen
–40 ... +70
–40 ... +70
–60 ... +70
–40 ... +60
–40 ... +60
–40 ... +50
Optical fiber
–50 ... +55
–40 ... +55
–40 ... +55
–50 ... +80
–50 ... +80
–50 ... +70
Copper lead of the cable
Operating tempera ture range, °C
+/–
+/–
+/–
+/–
+/–
+/–
+/+
+/+
+/+
+/+
+/+
+/+
Possibility of cable burial/ease of assembly
From 276
From 167
From 196
From 188
From 299
From 215
200
226
240
438
409
475
Cable weight per 1 km (kg)
(Yugtelekabel’..., 2013)
(VelkomSibir’, 2013)
(Gerda ..., 2013)
(Slavkabel’..., 2013)
(Gerda ..., 2013)
Source
SPECIFIC FEATURES OF SEISMIC STATION INSTALLATION 219
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