Magnitude 7.8 – OFF WEST COAST OF THE SOUTH ISLAND, N.Z.

2009Jul15NZ

A Magnitude 7.8 earthquake occurred today off the South Island of New Zealand.  This is the extracted signal from my seismograph in Holmes County, OH.

The focus of this earthquake is in the “core shadow” zone for my location.   The simple P or S body waves are “blocked” by the core but remnants of them which have been reflected or refracted by interactions at the surface, the outer liquid core, and the inner solid core do appear as what are called “core phases” and surface reflections.  The arrival times become difficult to interpret, with the arrival of many core phases occurring within small time periods.  The PP phase that does show clearly is the reflection of the P phase off the earth’s surface.  Here is a partial list of phases (from the USGS Arrival Time Calculator linked at the right hand side of the page) that may or may not be visible in the signature.  The nomenclature for these phase can be found here.

  DATE-(UTC)-TIME    LAT    LON     DEPTH MAG   Q   COMMENTS
  2009/07/15 09:22:32  45.72S 166.64E  35.0 7.8      US: OFF W. COAST OF S. ISLAN
   Expected 20s period surface wave amplitude [  1.93E+02 µm]  [  6.07E+01 µm/s]

 delta   azimuth (degrees clockwise from north)
 (deg)      eq-to-station     station-to-eq
131.12           70.2             239.9

                 travel   arrival time
    #  code      time(s)  dy hr mn sec
    1  Pdiff      959.31   0  9 38 31
    2  pPdiff     970.47   0  9 38 42
    3  sPdiff     974.74   0  9 38 46
    4  PKPdf     1148.12   0  9 41 40
    5  PKiKP     1148.89   0  9 41 40
    6  pPKPdf    1159.57   0  9 41 51
    7  pPKiKP    1160.33   0  9 41 52
    8  sPKPdf    1163.78   0  9 41 55
    9  sPKiKP    1164.54   0  9 41 56
   10  PP        1285.42   0  9 43 57
   11  SKPbc     1348.99   0  9 45  0
   12  SKPab     1349.60   0  9 45  1
   13  PKSbc     1353.24   0  9 45  5
   14  PKSab     1353.87   0  9 45  5
   15  SKPdf     1360.56   0  9 45 12
   16  SKiKP     1362.01   0  9 45 14
   17  PKSdf     1364.77   0  9 45 16
   18  SKSac     1574.64   0  9 48 46
   19  SKSdf     1577.01   0  9 48 49
   20  pSKSac    1590.24   0  9 49  2
   21  pSKSdf    1592.67   0  9 49  4
   22  sSKSac    1594.47   0  9 49  6
   23  sSKSdf    1596.88   0  9 49  8
   24  SKKSac    1697.61   0  9 50 49
   25  PKKPdf    1746.34   0  9 51 38
   26  Sdiff     1771.91   0  9 52  3
   27  pSdiff    1786.63   0  9 52 18
   28  sSdiff    1791.11   0  9 52 23
   29  SP        1894.18   0  9 54  6
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4 thoughts on “Magnitude 7.8 – OFF WEST COAST OF THE SOUTH ISLAND, N.Z.

  1. Dave,
    I assume you are talking about a seismograph and not an earthquake.

    Go for it. All things considered they are quite inexpensive. An old Windows computer, a $25 ADC, a magnet, lots of brass and stainless screws, some pipe fittings, and wire you have it. You need a simple amplifier too. It is easy to build but some parts (like winding the coil) are a little tedious (but you have more experience with coil winding than I have). I still have the spool of #34 wire from the back room…let me know when you need it. Actually, I have seen where someone used the coil out of a 240 volt relay as the sensor.

    Mic

  2. Yeah – it would be selfish of me to want a 7.9 earthquake in the “heartland”.

    I assume all the needed info is contained in your sidebar and the posts therein?

    I’ve got an old Compaq laptop with a fried hard drive – don’t know how much a replacement would be.

    D

  3. Yep, I think my Lehman Seismograph page has the basic idea. The Public Seismic Net page ( http://psn.quake.net/lehman.html ) has the text of the original Lehman article from Scientific American and the main page ( http://psn.quake.net/ ) has a lot of other information. The Loomis amplifier is good… http://users.viawest.net/~aloomis/seisprea.htm . Digi-Key and your friendly local electronics store have all the parts. The Dataq starter kit works well for $25. They’re just up in Akron so you’ll have it the next day after you order it. McMaster-Carr has magnets… http://www.mcmaster.com/#horseshoe-magnets/=2ray5b . You need 20-30 lb pull and a big enough gap to take your coil.

    It’s a great project…

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