Magnitude 7.0 – HAITI REGION

Raw seismogram of Magnitude 7.0 earthquake in Haiti as detected in northeast Ohio late this afternoon.

Moving Up in the World

A couple of weeks ago, in a telephone conversation, my older son mentioned that it would be interesting to see if we could measure the Doppler shift in a satellite radio beacon as it passed overhead. He suggested, if I was interested, that he could bring along a radio and we could try it when they came home to visit at Christmas. Of course I was interested!

After supper on Christmas evening, he found a candidate satellite and set up the radio. We fed the audio from the radio to the line input of my MacBook to make the recording and do the analysis. The long and the short of it was that we picked off a nice Doppler shift on two passes, one on the evening of the 25th and one on the evening of the 26th. The Raven Lite software was great for monitoring the signal, both visually and audibly but it had the shortcoming of limiting the recording time to only a minute. For the pass on the 26th, we split the signal and used his MacBook to record the full pass of several minutes into one file using Audacity while keeping Raven Lite running on mine. Since the frequency shift was greater than the radio’s passband, it had to be retuned a few times.

I picked several points off of each file and manually adjusted each point for the time and any retuning of the receiver as needed. Then I used my linear path model for the curve fit after replacing the speed of sound with the speed of light. The first pass data fit very nicely. I haven’t done the fit on the second pass yet. Once I do a little more analysis, I’ll put up a page on it.

My son reminded me that there was a docudrama on PBS’s Nova many years ago (December 1989) called “The School Boys Who Cracked the Soviet Secret” about a science class in a private boys school in England that did a similar analysis on the Sputnik satellite right after it was launched. It would be interesting to watch that again.

This is a very interesting subject that has lots of avenues to study in more detail. We’ll have to see what develops as time passes. For right now though, the basic process was pretty easy, gives me a lot of things to think about… and was very cool.

NetQuakes

The American Geophysical Union held their Fall Meeting in San Francisco this week. My wife heard a report on some of the happenings of interest to the general public on the radio this afternoon. One of the reports described the NetQuakes program being undertaken by the U.S. Geological Survey.

The NetQuakes program asks volunteers to host small seismographs at their homes in order to increase the number of seismographs in the San Francisco Bay area.  These appear to be strong motion sensors based on triaxial accelerometers and record data only when triggered by an acceleration of 0.25% g.  The triggered waveforms are sent to the USGS via wifi through the vounteer’s internet connection and are immediately analyzed for possible earthquake events.  The triggered waveforms are also displayed on a page off of the NetQuakes homepage. 

As I was exploring the NetQuakes site, I noticed that several, but not all the stations showed a coherent signal at about 10:16:30 on Dec 18, 2009.  I clicked on on one, J021-NC.  Then I went the USGS Earthquake Hazards page to look for small California earthquakes at that time.  I looked first at the listing for Magnitude 3+ events but didn’t find any at the proper time, which I should have expected from the limited number of stations reporting the event.  When I looked at the Magnitude 1+ list I found a Magnitude 1.8 earthquake just a few miles from the J021-NC station.  The station names can be determined by clicking on the location map at the location indicators…pretty cool and it should give them very fast earthquake severity and location information.

Help Needed… Aircraft Spectrum Analysis

Unknown Spectral Feature - Air Tractor Fixed Wing Aircraft

My search for Doppler shifted sounds has resulted in a number of recordings of aircraft. As I studied those recordings for the Doppler shift, I noticed that there was also another feature in the spectrograms that I didn’t understand. There is a shallow bowl shaped feature centered on the time of closest approach, ie when the aircraft was roughly overhead. The “bowl” seems to be formed by harmonic content in the signal. The frequency increases not only as the aircraft is approaching, as one would expect for a Doppler shift, but also as it moves away. The two spectrograms accompanying this post, for the Air Tractor fixed wing and the Chinook helicopter, show the feature pretty clearly.

I have thought about refraction due to the temperature lapse rate as a function of altitude but the equations don’t show any frequency dependence. I considered source directivity but I see it in two very different aircraft.  If you listen carefully to an airplane or helicopter flying over you can hear a frequency component that is increasing as the craft flies away from you…it seems to be a real phenomenon.  I am stumped!

Please comment if you know what causes this feature or if you have a suggestion as to what it might be.

Thanks.

Unknown Spectral Feature - Chinook Helicopter

Magnitude 6.6 – QUEEN CHARLOTTE ISLANDS REGION

A strong Magnitude 6.6 earthquake struck the Queen Charolette Islands region off the west coast of Canada at 15:30:46 UTC on November 17, 2009.  Because it was shallow, the surface waves were quite strong and were clipped on my seismograph here in northeatern Ohio.  The two types of surface waves, the Love and Rayleigh waves, are also very well delineated in their arrivals, which is often not the case.

The arrival time information from the USGS is included below:

  DATE-(UTC)-TIME    LAT    LON     DEPTH MAG   Q   COMMENTS
  2009/11/17 15:30:46  52.15N 131.38W  11.6 6.6      US: QUEEN CHARLOTTE ISLANDS
   Expected 20s period surface wave amplitude [  1.07E+02 µm]  [  3.36E+01 µm/s]
   Expected 1s period body wave amplitude     [  8.99E-01 µm]  [  5.65E+00 µm/s]

delta   azimuth (degrees clockwise from north)
(deg)      eq-to-station     station-to-eq
35.41           89.1             306.0

                 travel   arrival time
    #  code      time(s)  dy hr mn sec
    1  P          415.68   0 15 37 41
    2  pP         419.26   0 15 37 45
    3  sP         420.80   0 15 37 46
    4  PnPn       494.28   0 15 39  0
    5  PP         496.11   0 15 39  2
    6  PnPn       498.58   0 15 39  4
    7  PnPn       498.59   0 15 39  4
    8  PP         514.92   0 15 39 20
    9  PcP        565.21   0 15 40 11
   10  S          751.10   0 15 43 17
   11  pS         755.35   0 15 43 21
   12  sS         757.22   0 15 43 23
   13  ScP        790.89   0 15 43 56
   14  PcS        792.36   0 15 43 58
   15  SnSn       891.40   0 15 45 37
   16  SS         906.01   0 15 45 52
   17  SS         939.25   0 15 46 25
   18  PKiKP     1006.43   0 15 47 32
   19  pPKiKP    1010.42   0 15 47 36
   20  sPKiKP    1011.88   0 15 47 37
   21  ScS       1035.38   0 15 48  1
   22  SKiKP     1217.87   0 15 51  3
   23  PKKPdf    1901.07   0 16  2 27
   24  SKKPdf    2112.52   0 16  5 58
   25  PKKSdf    2113.98   0 16  5 59
   26  SKKSdf    2325.36   0 16  9 31
   27  P'P'df    2407.79   0 16 10 53
   28  P'P'ab    2498.68   0 16 12 24
   29  S'S'df    3259.19   0 16 25  5
   30  LQ         898.62   0 15 45 44
   31  LR         997.34   0 15 47 23

Cell Size and Scale

Here is a great illustration of the size of small things… Cell Size and Scale

(You drag the slider under the illustration to make things happen…)

A tip of the hat to Kathy and Craig for 1) finding it and 2) sharing it…

Magnitude 7.8 – VANUATU (and others)

Signals from four large earthquakes are embedded in the seismogram (northeast Ohio, USA)  displayed above. They are

Time                                  Magnitude                         Location

20:52:13, Oct 7                5.9                                     East of Severnaya Zemlya

21:41:14, Oct 7                 6.7                                     Celebes Sea

22:03:15, Oct 7                7.8                                     Vanuatu

23:13:49, Oct 7                7.1                                      Vanuatu

A quick look at the extracted signals clearly shows the Russian surface waves.  I think the 7.8 magnitude signal probably obliterates the one from the Celebes Sea which was quite deep and therefore lacking significant surface waves.  The surface waves from the second Vanuatu earthquake are visible.  Aside from the Celebes Sea earthquake the other three were relatively shallow.

Postscript:

The USGS just added another one:  Magnitude 7.7 – SANTA CRUZ ISLANDS at 22:18:26 UTC

Magnitude 7.6 – SOUTHERN SUMATRA, INDONESIA

A Strong Magnitude 7.6 earthquake occurred this morning at 10:16:09 UTC Southern Sumatra.  A tsunami watch statement was issued but appears to have been cancelled.  The image shows the seismic signal for the Sumatran earthquake at the bottom.  The Samoa Islands signal is still in the image at the top.

Magnitude 8.0 – SAMOA ISLANDS REGION

A Great Earthquake of Magnitude 8.0 occurred this afternoon, September 29, 2009 at 17:48:11 UTC in the Samoa Islands Region.  A significant local tsunami was generated.  The image is from my seismometer in Millersburg, Ohio, roughly 6960 miles away.

Magnitude 7.1 – IZU ISLANDS, JAPAN REGION

A Magnitude 7.1 Earthquake occurred this morning (10:55:56 UTC) off the coast of Japan.  This is the extracted earthquake from my seismograph in Holmes County, Ohio.

This seismogram has several interesting features.  The two largest peaks appear to be related to the S body waves as indicated by the arrival time table generated for my location by the USGS Arrival Time Calculator linked at the right and copied below.  The first large peak is the direct S wave phase but due to the exact location of the hypocenter relative to my location and to its depth of 303 km, the ScS phase arrives at exactly the same time.   The ScS phase is the reflection of the S phase off the core!  The other tall peak is the SS body phase which is due to one reflection of the S phase off the earth’s surface!

So why do the S phase arrivals show so strongly in this seismogram?  Notice that the station-to-eq azimuth in the table below is 327.1°.  My seismograph is oriented to be most sensitive to east-west motion and the S phase is a transverse vibration.  The first arrival was out of the northwest with the vibration transverse to that direction, ie roughly east-west.

The hypocenter was located at a depth of 303 km so there is a noticeable absence of surface waves when compared with earthquakes at shallower depths.

Here is the arrival time table:

  DATE-(UTC)-TIME    LAT    LON     DEPTH MAG   Q   COMMENTS
  2009/08/09 10:55:56  33.14N 138.04E 303.1 7.1      US: IZU ISLANDS, JAPAN REGIO
   Expected 1s period body wave amplitude     [  1.02E+00 µm]  [  6.40E+00 µm/s]
 
 delta   azimuth (degrees clockwise from north)
 (deg)      eq-to-station     station-to-eq
 97.92           29.6             327.1
 
                 travel   arrival time
    #  code      time(s)  dy hr mn sec
    1  Pdiff      781.30   0 11  8 57
    2  pP         853.74   0 11 10  9
    3  sP         885.48   0 11 10 41
    4  PP        1024.18   0 11 13  0
    5  PKiKP     1053.11   0 11 13 29
    6  pPKiKP    1129.12   0 11 14 45
    7  sPKiKP    1160.03   0 11 15 16
    8  SKiKP     1238.36   0 11 16 34
    9  SKSac     1388.76   0 11 19  4
   10  SKKSac    1417.53   0 11 19 33
   11  S         1440.19   0 11 19 56
   12  ScS       1440.19   0 11 19 56
   13  pSKSac    1491.85   0 11 20 47
   14  sSKSac    1523.95   0 11 21 19
   15  SP        1526.97   0 11 21 22
   16  pS        1534.98   0 11 21 30
   17  PS        1565.69   0 11 22  1
   18  sS        1570.00   0 11 22  6
   19  PKKPbc    1772.87   0 11 25 28
   20  PKKPdf    1776.94   0 11 25 32
   21  SS        1851.15   0 11 26 47
   22  SKKPdf    1962.24   0 11 28 38
   23  SKKPbc    1963.43   0 11 28 39
   24  PKKSdf    1993.16   0 11 29  9
   25  PKKSbc    1994.50   0 11 29 10
   26  SKKSdf    2178.30   0 11 32 14
   27  SKKSac    2183.63   0 11 32 19
   28  P'P'df    2269.45   0 11 33 45
   29  S'S'ac    3100.03   0 11 47 36
   30  S'S'df    3104.71   0 11 47 40
   31  LQ        2485.30   0 11 37 21
   32  LR        2758.33   0 11 41 54