Large Earthquake in Ohio?

With the recent earthquakes in Haiti and Chile I have been thinking about the earthquake potential here in Ohio. Unlike Haiti and Chile, Ohio is not on the edge of a tectonic plate. But we still have an earthquake now and then. Several years ago, I found a USGS website with the capability to plot the location of historical earthquakes in a given geographical area. I created a map, shown above, for earthquakes in the eastern United States.

Human beings have an innate capacity for seeing patterns, sometimes even where there are none. Being human, I can’t escape that tendency. When I look at my map, I see two broad lines of earthquakes, one on each side of the Appalachian mountains and running roughly parallel to the eastern coast of the country. I speculate that these earthquakes occur on cracks and faults in the earth’s crust that are remnants of the collisions and breakups of supercontinents hundreds of millions of years ago. While most of the earthquakes on the map are minor, a number of them have caused structural damage, most notably to chimneys and other masonry structures. A few have been large. The 1811-1812 series of earthquakes in the region around New Madrid, Missouri are among the largest known earthquakes the conterminous United States. That includes California! While they occurred prior to the invention of the seismograph the magnitudes of two of those earthquakes are estimated to have been between 7.2 and 8.0. These and several other large historical earthquakes in the eastern United States and Canada are listed below.

The New Madrid series, including:

1811, December 16, 08:15 UTC. Northeast Arkansas  Magnitude ~7.2 – 8.1

1811, December 16, 14:15 UTC, Northeast Arkansas

1812, January 23, 15:00 UTC, New Madrid, Missouri  Magnitude ~7.0 – 7.8

1812, February 7, 09:45 UTC, New Madrid, Missouri  Magnitude ~7.4 – 8.0

M7.3 Charleston, SC, 1886

Large earthquakes in southeastern Canada, including:

The 1925 Charlevoix-Kamouraska earthquake (Magnitude 6.2);

The 1929 Grand Banks (or Laurentian Slope) earthquake (Magnitude 7.2) which generated a 7 meter tsunami in Newfoundland;

The 1935 Timiskaming (or Témiscaming) earthquake (Magnitude 6.2);

The 1944 Cornwall-Massena earthquake (Magnitude 5.6).

The 1988 Saguenay earthquake (Magnitude 5.9).

There are a number of named seismic zones along the western line of earthquakes. The most famous is the New Madrid seismic zone but the Charlevoix-Kamouraska zone in Quebec also generates a lot of earthquake activity. Between those two there are other lesser known zones in southern Illinois/Indiana, western Ohio near Anna, and northeastern Ohio near Painsville. But the activity seems to thin out through Ohio…is that because that region is just more stable or is it because the stresses are still accumulating in the faults here? Could we have a large earthquake here in Ohio?

My amateur speculations are generally corroborated in the two page GeoFacts No.3 published by the Ohio Department of Natural Resources Division of Geological Survey. But my questions are not answered…the nature of Ohio’s subterranean faults is just not known.

Earthquakes are not something we live with on a daily basis in Ohio.  Most people in Ohio don’t even think about earthquakes.  I don’t expect a large earthquake here during my lifetime…but knowing what I know, however limited that knowledge is,  I won’t be surprised if there is one.

Magnitude 8.8 – OFFSHORE MAULE, CHILE

A Great Earthquake of Magnitude 8.8 occurred off the coast of Chile this morning at 06:34:14 UTC.  The extracted signal from my seismograph in northeastern Ohio shows severe clipping on the surface wave portion of the signal due to the size of this earthquake.  This earthquake was approximately 500 times stronger (energy released)  than the earthquake in Haiti last month.

The earthquake occurred offshore along the convergence zone of the Nazca and South American plates.  This is a thrust fault due to the subduction of the Nazca plate under the South American plate.  The earthquake occurred just 250 km north of the location of the largest earthquake recorded on instruments, a magnitude 9.5 event in May of 1960.   A series of significant aftershocks is expected.  One of these, at magnitude 6.9, occurred at 08:01:24 UTC.

The type of fault and its location and magnitude prompted several tsunami warnings and watches.  The following tsunami levels have been reported:

 Location                   Lat.   Lon.    Time        Amplitude
 ------------------------  -----  ------  -------     -----------

 40min     SAN FELX    C  26.3S   80.1W  0809UTC       0.69M/2.3FT
 27min     Corral  Chile   39.9S   73.4W  0727UTC      1.45M/4.8FT
 40min     Talcahuano  C   36.7S   73.1W  0659UTC      1.80M/6.0FT
           VALPARAISO  C   33.0S   71.6W  0708UTC      2.60M/8.6FT

Time - Time of measurement.
Amp. - Tsunami amplitudes are measured relative to normal sea  level.  It is NOT crest-to-trough wave
height.  Values are given in both meters (M) and feet (FT).

The phase arrival time information for my location is shown below:

 delta   azimuth (degrees clockwise from north)
 (deg)      eq-to-station     station-to-eq
 76.50          352.8             172.4

                 travel   arrival time
    #  code      time(s)  dy hr mn sec
    1  P          706.39   0  6 46  0
    2  pP         717.33   0  6 46 11
    3  PcP        717.67   0  6 46 11
    4  sP         721.65   0  6 46 15
    5  PP         878.25   0  6 48 52
    6  PKiKP     1050.19   0  6 51 44
    7  pPKiKP    1061.66   0  6 51 55
    8  sPKiKP    1065.86   0  6 51 59
    9  SKiKP     1261.00   0  6 55 14
   10  S         1290.15   0  6 55 44
   11  pS        1304.08   0  6 55 58
   12  sS        1308.82   0  6 56  2
   13  SKSac     1314.20   0  6 56  8
   14  SKKSac    1315.27   0  6 56  9
   15  ScS       1319.14   0  6 56 13
   16  SPn       1326.49   0  6 56 20
   17  pSKSac    1329.16   0  6 56 23
   18  PnS       1331.50   0  6 56 25
   19  sSKSac    1333.57   0  6 56 27
   20  SS        1586.24   0  7  0 40
   21  PKKPdf    1846.31   0  7  5  0
   22  PKKPbc    1858.17   0  7  5 12
   23  SKKPdf    2057.33   0  7  8 31
   24  PKKSdf    2061.53   0  7  8 35
   25  SKKSdf    2272.32   0  7 12  6
   26  P'P'df    2341.82   0  7 13 15
   27  S'S'df    3201.00   0  7 27 35
   28  S'S'ac    3212.35   0  7 27 46
   29  LQ        1941.66   0  7  6 35
   30  LR        2154.97   0  7 10  8

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.