A Magnitude 4.0 earthquake occurred in southern Michigan at 12:23 EDT this afternoon generating a very clean signal on my seismograph at Millersburg in northeastern Ohio. The analysis I did using jAmaseis estimated the distance to the epicenter to be 353 km. The Google Earth ruler measured 348.5 km. The signal overlaid on the jAmaseis travel time curves is shown below.
There was a moderate, Magnitude 5.0, earthquake in southern Ontario, Canada this morning. It registered as a small but nicely formed signal on my seismograph in northeastern Ohio, showing the P, S, and surface arrivals. The orientation of my seismograph makes it less sensitive to earthquakes north and south of my location than it is to earthquakes east or west of us. By my calculation this earthquake was about 456 miles northeast of my location.
USGS Event page is here: http://earthquake.usgs.gov/earthquakes/eventpage/usb000gxna#summary
The USGS reduced the magnitude estimate to 4.4 after this post was written.
A Major earthquake with a Magnitude of 7.5 occurred off the coast of southeastern Alaska today at 08:58:16 UT. Initial estimates predict low property damage and loss of life due ground shaking but tsunami warnings are in effect for a long much of the coast of southeastern Alaska and British Columbia down to Vancouver Island. The fault mechanism is shown to be a strike slip earthquake along what I think is a transform fault off the coast. The worst tsunamis are generated by dip slip earthquakes occurring on thrust faults.
Here in Ohio, the signal from my seismograph dominates the helicorder display. The extracted signal clearly shows the first arrivals of the P, PP, S, SS, and Love phases. The PP and SS phases are reflections of the respective body phases off of the earth’s surface (from the inside of course).
One of my first thoughts was where the earthquake was in relation to the grounded Shell drilling rig near Kodiak Island. My best estimate is that the rig is in a sheltered area about 725 miles west of the epicenter and probably (?) out of harms way from any tsunami.
Another major earthquake, a Magnitude 6.9 in the Gulf of California, overnight added to the unusual collection of strong earthquakes from yesterday. I continue to have the display gain reduced to 1 on the helicorder of my seismograph here in northeastern Ohio.
Today two earthquakes of magnitude greater than 8.0 (8.6 and 8.2) took place in the Indian Ocean off the coast of Sumatra in a span of just over two hours. One might expect only one or two earthquakes of this size worldwide in a year but here were two that were close together in both time and space. The helicorder display on my seismograph was unreadable. I normally keep it set to a gain of 4 but dropped it back to 1 this evening to view a Magnitude 6.5 earthquake in the Michoacan, Mexico that had been originally reported as Magnitude 7.0. Embedded in the signal in the lower part of the display is a Magnitude 5.9 earthquake off the coast of Oregon. The image above shows the helicorder display as recorded in northeastern Ohio.
As I looked at the tectonic setting in Sumatra this morning I noticed that the convergence rate of the subducting plate in the Indian Ocean where today’s large earthquakes occurred was 52 mm/yr. That compares to 77 mm/yr off the coast of Peru where we spent a week last month and which experienced a magnitude 8.0 earthquake and an associated tsunami in 2007. The devastation there was still very much in evidence five years later.
A Magnitude 4.0 earthquake was reported this afternoon at 20:04:58 UTC in northeastern Ohio. This is in the same area as a sequence of earthquakes thought to be associated with injection wells used to dispose of oil drilling waste fluids. The injection wells operations were suspended yesterday by the state of Ohio and the operator of the well.
Even though my seismograph in Millersburg, OH is not well suited to picking up local earthquakes and the display has been quite noisy the last few days, with a small amount of processing I did pick up a signal that appears to be caused by the earthquake in question.
The USGS arrival time information is shown:
DATE-(UTC)-TIME LAT LON DEPTH MAG Q COMMENTS 2011/12/31 20:04:58 41.16N 80.73W 2.2 4.0 us: YOUNGSTOWN-WARREN AREA, delta azimuth (degrees clockwise from north) (deg) eq-to-station station-to-eq 1.06 236.2 55.4 travel arrival time # code time(s) dy hr mn sec 1 Pg 20.39 0 20 5 18 2 sPg 20.92 0 20 5 18 3 Pb 21.09 0 20 5 19 4 pPb 21.44 0 20 5 19 5 sPb 21.83 0 20 5 19 6 Pn 21.88 0 20 5 19 7 pPn 22.41 0 20 5 20 8 sPn 22.74 0 20 5 20 9 Sg 35.19 0 20 5 33 10 Sb 36.46 0 20 5 34 11 sSb 37.05 0 20 5 35 12 Sn 38.13 0 20 5 36 13 sSn 39.00 0 20 5 37 14 PcP 510.96 0 20 13 28 15 ScP 722.84 0 20 17 0 16 PcS 723.12 0 20 17 1 17 ScS 935.02 0 20 20 33 18 PKiKP 994.23 0 20 21 32 19 pPKiKP 994.99 0 20 21 32 20 sPKiKP 995.27 0 20 21 33 21 SKiKP 1206.10 0 20 25 4 22 PKKPdf 1917.27 0 20 36 55 23 SKKPdf 2129.14 0 20 40 27 24 PKKSdf 2129.42 0 20 40 27 25 SKKSdf 2341.29 0 20 43 59 26 P'P'df 2428.55 0 20 45 26 27 S'S'df 3276.86 0 20 59 34
Several people have asked me about the triggering of earthquakes by hydraulic fracturing and waste injection wells. The USGS has a FAQ page on the subject.
I was busy yesterday and had missed the earthquake activity in Oklahoma. The Magnitude 5.6 event early this morning (UTC) shown in the bottom of the display, was large enough to trigger a notification to me from the USGS but the others were below the threshold that I had set. When I looked this morning I had also picked up the Mag 4.7 at 7:12:45 UTC shown toward the top of the display. The display shows the relative difference in the size of the waveform for two earthquakes at the same distance but with a 0.9 difference in magnitude. The larger earthquake released 22.4 times as much energy as the smaller one and should be about 7.9 times bigger on the seismograph.