Magnitude 6.9 – BAJA CALIFORNIA, MEXICO

A strong Magnitude 6.9 earthquake occurred at the northern end of the Gulf of California this evening at 22:40:39 UTC.  The surface wave signal went offscale for roughly 15 minutes on my seismograph in northeastern Ohio.

The travel time information is shown below:

  DATE-(UTC)-TIME    LAT    LON     DEPTH MAG   Q   COMMENTS
  2010/04/04 22:40:39  32.09N 115.25W  32.3 6.9      CI: BAJA CALIFORNIA, MEXICO
   Expected 20s period surface wave amplitude [  3.14E+02 µm]  [  9.88E+01 µm/s]
   Expected 1s period body wave amplitude     [  2.69E+00 µm]  [  1.69E+01 µm/s]

 delta   azimuth (degrees clockwise from north)
 (deg)      eq-to-station     station-to-eq
 28.05           63.0             263.1

                 travel   arrival time
    #  code      time(s)  dy hr mn sec
    1  P          348.27   0 22 46 27
    2  pP         357.60   0 22 46 36
    3  sP         361.79   0 22 46 40
    4  pP         362.32   0 22 46 41
    5  sP         366.59   0 22 46 45
    6  PnPn       396.29   0 22 47 15
    7  PP         411.89   0 22 47 30
    8  PcP        542.03   0 22 49 41
    9  S          631.62   0 22 51 10
   10  pS         642.31   0 22 51 21
   11  sS         647.64   0 22 51 26
   12  SPg        649.31   0 22 51 28
   13  SnSn       709.29   0 22 52 28
   14  ScP        760.33   0 22 53 19
   15  PcS        764.25   0 22 53 23
   16  ScS        992.93   0 22 57 11
   17  PKiKP      997.98   0 22 57 16
   18  pPKiKP    1008.66   0 22 57 27
   19  sPKiKP    1012.55   0 22 57 31
   20  SKiKP     1206.72   0 23  0 45
   21  PKKPdf    1903.14   0 23 12 22
   22  SKKPdf    2111.88   0 23 15 50
   23  PKKSdf    2115.77   0 23 15 54
   24  SKKSdf    2324.45   0 23 19 23
   25  P'P'df    2411.51   0 23 20 50
   26  P'P'ab    2527.79   0 23 22 46
   27  S'S'df    3258.93   0 23 34 57
   28  LQ         711.89   0 22 52 30
   29  LR         790.10   0 22 53 49

Postscript:

USGS subsequently re-estimated the magnitude to be 7.2 and raised the hypocenter estimate from ~32 km to 10 km.

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2 thoughts on “Magnitude 6.9 – BAJA CALIFORNIA, MEXICO

  1. 15 minutes off scale… in Ohio…. that blows my mind

    Have you ever seen that much off-scale activity? I know it was a lot closer than most… but…

  2. I wish I knew what the scale is/was. My calibration check is to make sure that I get 60%-80% of full scale when I walk up and stand beside the sensor on my basement floor.

    To answer your question, yes, it goes off scale rather often, depending on the magnitude, the distance, the depth of the focus, and the details of the focal mechanism. The big one in Chile in February was off scale for 25 minutes or more. These big earthquakes are pretty amazing. The displacement due to the Sumatra Andaman Island earthquake back in 2004 was measured to be 1 cm in Scotland, about as far away from the epicenter as you can get.

    The dynamic range of my seismograph is not large enough to handle the range that I want/need to see. I have the amplification about as high as I can get it without getting a lot of noise due to the wind in the trees and against the house. I still don’t see all of the US earthquakes that I think I ought to see. But with the amplification that high, I intentionally sacrifice the details in the really big ones just because of my limited dynamic range. I think the professionals use 24 bit ADCs. Mine is 10 bits. That’s probably more than you wanted to know about it…

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