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Hough, S.E., K. Mueller,
R. Bilham, N. Ambraseys, and S. Martin, "Remotely triggered
earthquakes in Intraplate Regions: Distributed Hazard, Dependent
Events", EOS, Transactions of the American Geophysical Union 84
(46), Fall Meeting, Abstract S31G-07., 2003. |
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Abstract: The
central and eastern United States has experienced only 5 historic
earthquakes with Mw above 7.0, the 1886 Charleston earthquake and
four during the New Madrid sequence of 1811-1812 (three principal mainshocks and the so-called ``dawn aftershock'' following the first
mainshock.) Careful consideration of historic accounts yields
compelling evidence for a number of remotely triggered earthquakes
in both 1812 and 1886, including several events l |
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arge enough to be potentially damaging.
We propose that one of the (alleged) New Madrid mainshocks, on 23 January 1812, may itself be a remotely
triggered earthquake, with a location some 200 km north of the New
Madrid Seismic Zone. Our proposed source location is near the
location of the 1968 southern Illinois earthquake, which occurred on
a blind thrust fault at 20-25 km depth. Intensity data for the 1812
event are consistent with expectations for a similarly deep event.
Such triggered events presumably do not represent a wholly new
source of hazard but rather a potential source of dependent hazard.
That is, the common assumption is that the triggering will
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cause only a "clock
advance,'' rather than causing earthquakes that would not have
otherwise occurred. However, in a low strain-rate region, a given
dynamic stress change can potentially represent a much larger clock
advance than the same change would cause in a high strain-rate
region. Moreover, in regions with low seismicity and a short
historic record, overlooked remotely triggered historic earthquakes
may be important events. It is thus possible that significant events
are currently missing from the historic catalogs. Such events--even
if large--can be difficult to identify without instrumental data.
The (interplate) 1905 Kangra, India earthquake, further illustrates
this point. In this case, early seismic records provide
corroboration of an early triggered event whose existence is
suggested--but difficult to prove--based on detailed macroseismic
data. In the central United States, where even moderate earthquakes
are uncommon, our results suggest that the largest known historic
earthquakes in three states (Kentucky, Illinois, and Mississippi)
may have been remotely triggered earthquakes. |
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