To carry out such conversions requires minimal calculation, therefore a simple
programming language is sufficient. Quickbasic is well suited, as it will run on any
...
PII:
Computers & Geosciences Vol. 24, No. 6, pp. 585±590, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain S0098-3004(98)00056-9 0098-3004/98/$ - see front matter
SHORT NOTE DATACON: A QUICKBASIC PROGRAM TO REFORMAT ORIENTATION DATA FROM FAULTS CHRISTOPHER SHORROCK*, and RICHARD J. LISLE Laboratory for Strain Analysis, Department of Earth Sciences, University of Wales, Cardi CF1 3YE, U.K. (Received 14 July 1997; revised 15 January 1998) Code available at http://www.iamg.org/CGEditor/index.htm
INTRODUCTION
CONVERSION OF STRUCTURAL DATA
Palaeostress analysis aims to infer the nature of ancient stresses responsible for the development of geological structures. Such analyses are often carried out using orientation data collected from fault planes and their associated slip lineations. A wide range of methods have been developed to carry out fault-striation analysis, a comprehensive review of which is provided by Angelier (1994). It is possible to specify the orientation of a fault surface and its associated slip direction by the means of a few variables, e.g. two to describe the attitude of the fault and a third to indicate the orientation of the slip direction within the plane of the fault. In practice this basic information is recorded in a great variety of ways, because structural geologists have preferences for dierent conventions of measuring and recording ®eld data. This has consequently resulted in computer programs being written to analyse such data (in terms of palaeostresses), that have been designed to accept data only with a particular format. Since existing palaeostress programs dier with respect to their assumptions and in the presentation of results, it is often found desirable to analyse the same data using a number of dierent programs and to compare the results. When this is attempted however, the diering input parameters required by the various programs means that tedious preliminary stages of data conversion must be undertaken. The purpose of this program is to facilitate this necessary data conversion. To carry out such conversions requires minimal calculation, therefore a simple programming language is sucient. Quickbasic is well suited, as it will run on any IBM compatible microcomputer system.
The number of variables which are frequently used to de®ne the orientation of a fault plane together with its movement direction and sense exceeds twenty. The program is designed to convert between such variables or combination of variables. Conversions for speci®c pairs of variables (e.g. calculating dip azimuth of the fault plane from the strike) are performed in separate subroutines. However the number of subroutines required for all conceivable combinations of input and output variables would be excessive. In order to reduce the number of subroutines needed, a strategy is adopted which ®rstly converts the input data into a ``standard format''. Once in standard form the data can then be converted into the desired variables. We have chosen a standard format on the basis of simplicity. This format is an adaptation of a spherical plot technique described by Fry (1992). In this, fault-striation orientations are described in terms of three quantities: (a) The angle of dip of the fault plane; (b) The dip azimuth of the fault plane. (c) The pitch of the striation within the fault, described by a three ®gure number which also incorporates information on the displacement sense displayed by the fault. Such a format can be recognised as providing an economical and easy-to-use method of recording fault-striation data. The authors feel that this format could go someway to providing a standard technique for the recording of such data. The conversion of data by running DATACON consequently follows a series of steps (Fig. 1): (1) Firstly the name of the input ®le is requested. (This will have already been created in a text ®le editor. The text ®le follows a layout, where each fault-striation description is con®ned to one row, and the data pertaining to that structure is situated
*E-mail:
[email protected]. 585
586
Short Note
within columns that are explicit to each of the utilised variables. Each fault datum is separated by commas.) (2) The name of the ®le to which the converted data is to be saved is then requested. (3) The user then speci®es the variables corresponding to each column of the input data ®le. (4) Finally the variables that will describe each of the data columns of the output ®le are speci®ed.
DATA CONVENTIONS
Azimuth convention This records orientation data as a direction in the range 0±3608 measured clockwise round from North. For example, due West is described as 270 in azimuth convention. Quadrant convention This system described by Marshak and Mitra (1988), records orientation data in degrees in relation to the four quadrants of the compass. Depending on the quadrant, directions are speci®ed relative to either North or South, with the angle measured in degrees towards either the East or West. For example 010, 100, 180 and 270 in the azimuth convention are N10E, S80E, S0E (or S0W) and N90W (or S90W), respectively. Quadrant description This gives an approximation of the dip direction of a plane and the plunge or pitch of a lineation according to the four points of the compass, or any combinations of the four (e.g. N, E, S, W, NW, SE, NNW, ESE, etc.). Its use lies in the speci®cation of such a measurement when only limited information is otherwise provided. Right-hand-rule convention This system used for recording the orientation of planes, obviates the need to specify the direction of dip explicitly. By choosing to quote the strike direction that lies 908 away from the dip direction measured in a clockwise fashion, the dip becomes unambiguous. This convention can be described by the recording of strike ``in the direction that the right index ®nger points when the thumb points down the dip (and the palm is facing the recorded surface)'' (Barnes, 1991). Left-hand-rule convention This ful®ls the same purpose as the right-handrule, but here the orientation of strike is selected by the direction of the index ®nger of the left hand when the palm is face down upon the planar surface, with the thumb pointing in a down dip direction.
Figure 1. Flow diagram of procedure to convert faultstriation data from one format to another INPUT AND OUTPUT VARIABLES
DATACON accepts 23 dierent types of input and output data. The composition of the input ®le in terms of the number and type of data is speci®ed by the user with the aid of a variables list presented on-screen. The desired format of the output ®le is chosen in a similar fashion. The supplied variable options attempt to describe comprehensively all known forms of recording orientation, inclination, motion sense and any other related information. Similarly keyboard input of text is not case sensitive. In some instances the choice of one variable alone from the INPUT FILE menu is sucient to allow the conversion of the selected data into one or more forms of output, chosen from the OUTPUT FILE menu. However in most cases one or more further related input variables will be required to enable the conversion of the selected input data into the required output variable/variables. For example; where striation geometry and sense are required for their conversion to the third
Short Note
587
Variable 5: strike (0±3608) This is the strike of the plane recorded in azimuth convention. At input either of the two azimuths (1808 apart) can be supplied. With the input of strike, if the corresponding dip direction is not supplied only that which has been input will be available for output. In cases where dip direction is input, rather than a strike value; the strike information provided for variable 5 will correspond to strike, right-hand-rule. Variable 6: strike (0±3608), right-hand-rule This is the plane's strike in azimuth convention, following the right-hand-rule system. Variable 7: strike (0±3608), left-hand-rule The strike is speci®ed in azimuth convention, according to the left-hand-rule system. Variable 8: strike, quadrant convention This describes the same data as variable number 5, but the direction is speci®ed by the quadrant convention. Variable 9: strike, quadrant convention, righthand-rule In this case a combination of the quadrant and right-hand-rule conventions is utilised to describe strike. Variable 10: strike, quadrant convention, left-handrule In this case a combination of the quadrant and left-hand-rule conventions are employed to describe strike.
variable of the authors standard format for the description of fault-striation data (i.e. converting from variables 11, 12 and 21 to variable 18). If a case arises where not enough data is supplied for the requested conversion to be made, the output ®le displayed through a text ®le editor will produce a column that will be either: blank in the case of an alphabetic output, or will contain ``999'' in the case of a numeric output, with the ``label'' variable in turn being displayed by ÿ100 (so as to avoid confusion with a datum numbered 999). If a variable is input and then output, the values may not be equal. This is the case when input data are mutually con¯icting. The 23 variables are grouped under four dierent headings: fault plane, lineation, sense of slip and identi®cation. Each group relating to the description of one of the four main categories of data required for the completion of a structural data analysis.
Fault plane The various methods of describing a fault plane are detailed below. In order to understand best the requirements for, and the results of, the conversion between these methods by DATACON, it is recommended that this section is read in conjunction with reference to Table 1. Variable 1: angle of dip (0±908) From the input of the angle of dip only, DATACON cannot carry out any conversions. Variable 2: dip direction (0±3608) This is recorded in azimuth convention and relates to the orientation of the angle of dip. Variable 3: dip direction, quadrant convention This eectively describes the same information as variable 2, but utilises the quadrant convention. Variable 4: quadrant of dip direction This provides an approximation of the data described by variable 2. It refers to a point of the compass for which there is a component of dip. For example a plane having a dip direction of 010 could equally be described by the North or East compass point.
Lineation In order to understand best the dierent methods of describing fault-striation interactions and the conversions between them by DATACON, it is recommended that this section is read in conjunction with reference to Table 2. Variable 11: angle of plunge (0±908) An angle describing the vertical declination of the lineation. Conversions from this variable to another, can only be made when ``angle of plunge'' is accompanied by either variable 12, 13 or 14. Variable 12: plunge direction (0±3608) This is recorded in azimuth convention and records the orientation of the angle of plunge. Conversions from this variable do not require the accompaniment from variable 11.
Table 1. Examples of various methods of recording fault-plane orientations that can be converted between and produced by variables included in DATACON Variables 2 0 45 90 135 180 225 270 315 360
3
4
5
6
7
8
9
10
N0E N45E N90E S45E S0W S45W N90W N45W N0W
N E E S S W W N N
90 135 180 225 270 315 0 45 90
90 135 180 225 270 315 0 45 90
270 315 0 45 90 135 180 225 270
N90E S45E S0W S45W N90W N45W N0E N45E N90E
N90E S45E S0W S45W N90W N45W N0E N45E N90E
N90W N45W N0E N45E N90E S45E S0W S45W N90W
588
Short Note Table 2. Examples of dierent manners by which complete fault-striation interactions, (®rstly described by three central variables 1: ``angle of dip'', 2: ``dip direction'' and 18 ``pitch incorporating slip sense, taken clockwise from strike (0±3608)'' can be described or can be converted between with DATACON Variables 1
2
18
11
12
13
14
15
16
17
5 10 15 30 40 55 65 75 90
180 225 270 315 360 0 45 90 135
0 45 90 135 180 225 270 315 360
0 7 15 21 0 35 65 43 0
90 179 270 4 90 299 45 165 225
N90E S1E N90W N4E N90E N61W N45E S15E S45W
E S W N E W E S W
0 45 90 45 0 45 90 45 0
E S S E E W N S W
0 45 90 135 180 45 90 135 180
Variable 13: plunge direction, quadrant convention This is the direction of plunge of the linear structure given in quadrant convention. Variable 14: quadrant of plunge A compass quadrant for which a linear structure has a component of plunge. Variable 15: angle of pitch (0±908) This is the acute angle measured in the fault plane between the strike of the fault and the lineation. Starting from the strike line, the angle is measured in a sense which is down the dip of the plane. This is used in conjunction with variable 16. Variable 16: quadrant of pitch The variable is used to indicate the direction of the strike from which the angle of pitch (variable 15) is measured. Variable 17: pitch, taken clockwise from strike (0± 1808) This is the angle measured in the fault plane between the strike given by the left hand rule and the lineation. The angle is recorded in a clockwise sense (looking down upon the fault plane) and has a range from 0 to 1808, Figure 2(a). This conveys equivalent information to a combination of variables 15 and 16. Sense of slip Conversion between variables; 18, 19, 20 and 21, allows the alteration of the user's rough and often geometrically imperfect description of fault slip sense, to one that is geometrically acceptable. Variable 18: pitch incorporating slip sense, taken clockwise from strike (0±3608) This convention (described by Fig. 2B) based upon a method described by Fry (1992), combines the information provided by variable 17, with the sense of movement displayed by the given fault plane. The angle is measured between the strike (given by the lefthand-rule) and the lineation, in a clockwise sense (looking down upon the fault plane). However, the angle has a range from 0 to 3608 in this case. The ®rst 1808 (forming the down-dip arc of the fault plane), are used to describe those faults whose sense of motion displays a component of normal slip. The up-dip range from 180 to 3608 is used to describe those faults with a reverse sense of displa-
Figure 2. (A) Striated dipping fault surface, displaying convention used in Variable 17: ``Pitch taken clockwise from strike (0±1808)'', to record pitch and pitch quadrant in three ®gure datum. Example shows that by measuring angle between strike, left-hand-rule (shown as 0), and lineation lying in down-dip arc of fault surface, we obtain a result of 135. (B) Same surface is used to display convention used in Variable 18: ``Pitch incorporating slip sense, taken clockwise from strike (0±3608)'' to record pitch, pitch quadrant and displacement sense in one three®gure datum. Example shows that by measuring angle between strike, left-hand-rule (shown as 0) and lineation displaying sense of motion of missing fault block, we obtain a result of 135 in case of this normal motion. (Reverse fault motion would, in this case provide a result of 315)
Short Note
589
Table 3. Examples of some of more popular palaeostress analysis packages and their input formats. Detailing order in which speci®ed data variables are required for running of these programs Authors Hardcastle (1989) Hardcastle (1989) Hardcastle and Hills (1991) Sperner and others (1993) Nemcok and Lisle (1995) Lisle (1988) Ciscato (1996)
Program
No. of Variable Variable Variable Variable Variable Variable Variable variables No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7
BRUTE 3 RECHES 4 SELECT
6 6 6
7 7 7
1 1 1
12 12 12
11 11 11
19 19 19
22 22 22
INVERS
7
2
1
12
11
19
22
FLTCLAN
6
5
1
12
11
19
20
ROMSA RIGHT TRIHEDRA
6 6
1 1
2 2
11 11
12 12
19 19
20 20
cement. Pure sinistral or dextral strike-slip motion, results in an output of 0 and 1808, respectively. ``Pitch taken clockwise from strike'' therefore provides an economical method of recording three pieces of information in one easy-to-read datum. Due to the method's virtue of compactness it has been chosen as the last of the three central components of the DATACON program. Variable 19: normal or reverse Given the wide variety of personally preferred notations used for the recording of normal and reverse motion, DATACON allows the user to de®ne his or her own input and output slip sense notation. This is done by a prompt from the program for the user to input their chosen abbreviation for normal and reverse. These should be typed; separated by a comma. Thus full length words, parts of words, abbreviations, single letters and ®gures can be utilised to provide descriptors for both normal and reverse. Variable 20: dextral or sinistral Similar to variable number 18, DATACON allows the user to de®ne labels in the input and output ®les to specify dextral and sinistral movement senses. Variable 21: normal, reverse, dextral or sinistral DATACON allows any form of normal, reverse, dextral or sinistral slip notation to be used by the program at both input and output stages of the conversion of the slip data. Variable 22: con®dence of slip sense (1±10) Field assessment of the sense of movement is not always unambiguous. Therefore an index of con®dence is sometimes used to quantify the degree of certainty in the determined sense of slip. This variable does not convert into any other variable and therefore the user can choose to avoid this variable, to utilise only part of the range (e.g. 1 to 4), or to use the range in either ascending or descending order in accordance with the degree of con®dence. Similarly the output for variable 22 will therefore remain the same as the input. However this will allow the incorporation or addition of this variable at the time of conversion of any other data from the data®le in question and it will also negate the
23
need to delete it from data®les that will be converted. Identi®cation Variable 23: fault label This is an identi®er of the fault and can take the form of either numbers, names or comments, but must not include any spaces or punctuation marks (e.g. ``Faultnumber1carboniferouslimestoneSouthWales''). It is not subject to conversion. DATA FILES FOR EXISTING PROGRAMS
The 23 input and output variable options are provided so as to allow the implementation of all programs presently available that deal with such information, with particular emphasis on palaeostress analysis. Table 3 displays examples of data format for some commonly used programs. It describes their input layouts and variable options, for use in conjunction with DATACON, and consequently with each other. AcknowledgmentsÐThe authors wish to thank Kenneth Hardcastle, B. Ciscato, M. Nemcok, B. Sperner, L. Ratschbacher and R. Ott for allowing wide access to their computer packages. We are grateful to Norman Fry for his comments upon the ``standard format''.
REFERENCES Angelier, J. (1994) Fault slip analysis and palaeostress reconstruction: In Continental Deformation, ed. P. L. Hancock, pp. 53±100. Pergamon Press, Oxford. Barnes, J. (1991) Basic Geological Mapping, 2nd edn. Open University Press, Milton Keynes, 119 pp. Ciscato, B. (1996) Principal stress orientations from faults: a C++ program. In Structural Geology and Personal Computers, ed. D. G. De Paor, pp. 325±342. Pergamon Press, Oxford. Fry, N. (1992) Stress ratio determinations from striated faults: a spherical plot for cases of near-vertical principal stress. Journal of Structural Geology 14(10), 1121± 1131. Hardcastle, K. C. (1989) Possible paleostress tensor con®gurations derived from fault-slip data in Eastern
590
Short Note
Vermont and Western New Hampshire. Tectonics 8(2), 265±284. Hardcastle, K. C. and Hills, L. S. (1991) Brute3 and Select: Quickbase 4 programs for determination of stress tensor con®gurations and separation of heterogeneous populations of fault-slip data. Computers & Geosciences 17(1), 23±43. Lisle, R. J. (1988) ROMSA: A Basic program for palaeostress analysis using fault-striation data. Computers & Geosciences 14(2), 255±259.
Marshak, S. and Mitra, G. (1988) Basic Methods of Structural Geology. Prentice-Hall, New Jersey, p. 446. Nemcok, M. and Lisle, R. J. (1995) A stress inversion procedure for polyphase fault slip data sets. Journal of Structural Geology 17(10), 1445±1453. Sperner, R., Ratschbacher, L. and Ott, R. (1993) Faultstriae analysis: A Turbo Pascal program package for graphical presentation and reduced stress tensor calculation. Computers & Geosciences 19(9), 1361±1388.
