Magnitude 3.9 - UTAH
2007 August 06 08:48:40 UTC
- This event has been reviewed by a seismologist.
|Depth||1.6 km (~1.0 mile)|
|Distances||40 km (25 miles) WSW of Price, Utah|
60 km (35 miles) ESE of Nephi, Utah
80 km (50 miles) SSE of Spanish Fork, Utah
155 km (95 miles) SSE of SALT LAKE CITY, Utah
|Location Uncertainty||horizontal +/- 0.4 km (0.2 miles); depth +/- 1 km (0.6 miles)|
|Parameters||Nph= 33, Dmin=18.9 km, Rmss=0.19 sec, Gp= 47°,|
M-type=local magnitude (ML), Version=5
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A shallow seismic event, magnitude 3.9, was recorded on stations of the USGS Advanced National Seismic System at 02:48 AM MDT on August 6, 2007. The event was located in the vicinity of the Crandall Canyon Mine in the Wasatch Plateau coalfield of east-central Utah. Abundant mining-induced seismicity and less frequent natural earthquake activity have been instrumentally recorded in this area for decades. The largest of past seismic events related to mining activity in this region had magnitudes in the 3.5 to 4.2 range.
The M3.9 event does not have the characteristics of a typical, naturally occurring earthquake. Instead, preliminary observations suggest a shock induced by underground coal mining. Detailed seismological analyses by scientists at the University of California at Berkeley support this interpretation. The findings of the Berkeley team indicate that the source mechanism of the August 6 seismic event is most consistent with the collapse of an underground cavity ( http://seismo.berkeley.edu/~peggy/Utah20070806.htm).
Twelve seismic events were recorded by the regional seismic network in the first 38 hours following, and in the vicinity of, the large event of August 6. These smaller events range in magnitude from less than 1.0 to 2.2. A shock of magnitude 2.1 occurred about 17 hours after the main event (at 8:05 PM MDT, August 6); another of magnitude 2.2 occurred about five hours later (at 01:13 AM, August 7). These shocks are interpreted to reflect settling of the rockmass following a cavity collapse.
Scientific & Technical Information
- Preliminary Earthquake Report
- University of Utah Seismograph Stations