The present HYP071PC distribution disk contains the following six files:(1) README a copy of this note. ( 2) HYP071PC.EXE executable code for the program HYP071PC. (3) INPUTSTA.EXE executable code for helping you to enter station data. (4-) INPUTPHA.EXE executable code for helping you to enter phase data. (5) HYP071.INP test data from the original HYP071 program. (6) HYP071.0UT output file by HYP071PC using HYP071.INP as input data.This distribution disk is NOT bootable. The reason for making this change is that many users prefer to boot the PC with their own disk. In order to run HYP071PC, you must have at least 256K bytes of RAM, a math coprocessor (Intel 8087 or 80287), and the operating system must be DOS 2.1 or higher. You must also have enough room ( >4-0K bytes) in your default disk for output.To check the files on the disk you received, please make a test run using the file HYP071.INP as input (see attached Manual for details). Answer the prompt for the input data filename by typing HYP071.INP and press the ENTER key. Please note the default choice (by pressing only the ENTER key) is for a file called HYP071PC.INP which is NOT on the distribution disk. The word HYP071 contains 2 parts: (1) the letters H.Y.P.O (not zero), and (2) the numbers 7 and 1.You may answer the prompts for the output print and punch files by pressing the ENTER key; the output will then be written in files called HYP071PC.PRT and HYP071PC.PUN. Actually, there is no punch output for the test input file HYP071.INP, but a file called HYP071PC.PUN is created anyway. The program should terminate with the message Execution terminated : 0.Next, compare the file HYP071PC.PRT with the file HYP071.0UT on the distribution disk by using the COMP command (read your DOS Manual for the COMP command). These two files should be identical and compared O.K.; if not, you may have a bad distribution disk (possibly caused by mailing).Abnormal termination of HYP071PC during execution is usually indicated by an error message on your display screen with an error number. Consult the IBM Professional Fortran Manual for explanations (Appendixes in the Installation and Use binder list the Runtime error messages). The fallowings are some examples: (1) Error Number 4-001 No math coprocessor; you need £o install a math coprocessor (Intel 8087 or 80287 chip) in your PC. (2) Error Number 4-002 Wrong DOS, i.e., you need DOS 2.1 or later versions. (3) Error Number 3000'sProblems in reading or writing from disk. Check for enough space on your default disk to hold the output. The size of the output files depend on your choices and are usually ten times larger than your input file size. If you have enough space, then make sure your disk is good (i.e., you should be able to display your input file on screen), and is NOT write protected.If you have problems, contact Willie Lee (415-323-8111 ext. 2630), or mail him a copy of your input file on a disk & tell him the problems you have. A copy of the FORTRAN source code for HYP071PC is also available upon request (with a blank ...

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The Petatlan earthquake of March 14, 1979 (Ms = 7.6), occurred between the Middle America trench and the Mexican coast, 15 km southwest of Petatlan, Guerrero, Mexico. From seismograms recorded on smoked paper, FM, and digital tapes, we have identified 255 aftershocks with coda lengths greater than 60 s that occurred 11 hours to 36 days after the main shock. Based on these events, the aftershock epicentral area defined during the period be, tween 11 and 60 hours was about 2000 km2; between 11 hours and 6 days it was about 2400 km 2. Although the area grew to 6060 km 2 in 36 days, most of the activity was still confined within the area defined after 6 days. This suggests that the smaller aftershock area might represent an asperity. The distribution of events and energy release per unit area confirm the existence of heterogeneity in the aftershock area. Thus our data support the concept of an inhomogeneous rupture area that includes an asperity, as suggested by Chael and Stewart (1982) to account for the differences they computed for the body and surface wave moments from WWSSN data. However, the combination of the moments Reichle et al. (1982) report for body and surface waves from IDA data and the rupture areas reported in this paper results in a solution that is most physically realizable in terms of stress drop and slip. We calculate stress drops of 5 and 15 bars, the former for the average over the entire area, the latter for the asperity, and an average slip of 60 cm for the entire area and 120 cm for the asperity. These values for slip are 30% and 60%, respectively, of the convergence of the Cocos plate relative to the North America plate during the 36-year period between the last two major earthquakes in the Petatlan area. Hypocenters of the aftershocks define a zone about 25 km thick, dipping 15 ø with an azimuth of N20øE, which is perpendicular to the Middle America trench. Most aftershocks are below the main shock. The b value estimated for aftershocks in the range 3.0 -< MoL --< 4.5 is 60% higher than one determined similarly by Hsu (1981) for the foreshocks.