Intraplate Triggered Earthquakes: Observations and Interpretation

Abstract

We present evidence that at least two of the three 1811-1812 New Madrid, central United States, mainshocks and the 1886 Charleston, South Carolina, earthquake triggered earthquakes at regional distances. In addition to previously published evidence for triggered earthquakes in the northern Kentucky/southern Ohio region in 1812, we present evidence suggesting that triggered events might have occurred in the Wabash Valley, to the south of the New Madrid Seismic Zone, and near Charleston, South Carolina. We also discuss evidence that earthquakes might have been triggered in northern Kentucky within seconds of the passage of surface waves from the 23 January 1812 New Madrid mainshock. After the 1886 Charleston earthquake, accounts suggest that triggered events occurred near Moodus, Connecticut, and in southern Indiana. Notwithstanding the uncertainty associated with analysis of historical accounts, there is evidence that at least three out of the four known M W 7 earthquakes in the central and eastern United States seem to have triggered earthquakes at distances beyond the typically assumed aftershock zone of 1-2 mainshock fault lengths. We explore the possibility that remotely triggered earthquakes might be common in low-strain-rate regions. We suggest that in a low-strain-rate environment, permanent, nonelastic deformation might play a more important role in stress accumulation than it does in interplate crust. Using a simple model incorporating elastic and anelastic strain release, we show that, for realistic parameter values, faults in intraplate crust remain close to their failure stress for a longer part of the earthquake cycle than do faults in high-strain-rate regions. Our results further suggest that remotely triggered earthquakes occur preferentially in regions of recent and/or future seismic activity, which suggests that faults are at a critical stress state in only some areas. Remotely triggered earthquakes may thus serve as beacons that identify regions of long-lived stress concentration.

Lithospheric velocity structure of the New Madrid Seismic Zone: A joint teleseismic and local P tomographic study

“…Three stars show the estimated epicenters of the 1811-1812 M w ! 7.0 events [Johnston and Schweig, 1996;Hough et al, 2003]. Two diamonds show the estimated locations of the 1843 Marked Tree, Arkansas earthquake (M $ 6.3) and the 1895 Charleston, Missouri earthquake (M $ 6.6), respectively [Johnston, 1996].…”

“…The microseismicity delineates three linear faults in the NMSZ ( Figure 1): (1) the NE-trending Blytheville Fault Zone (BFZ), (2) the NW-trending Reelfoot Fault (RF), and (3) the NNE-trending New Madrid North Fault (NN) [Johnston and Schweig, 1996]. The largest events including the 1811 -1812 main shocks [Johnston and Schweig, 1996;Hough et al, 2003], the 1843 Marked Tree, Arkansas earthquake (M $ 6.3), and the 1895 Charleston, Missouri earthquake (M $ 6.6) [Johnston, 1996] are thought to have occurred on those faults (Figure 1). Paleoseismologic studies also suggest that several large earthquakes similar to the 1811 -1812 sequence have happened in the NMSZ in the past a few thousand years [Tuttle et al, 2002].…”

Remotely Triggered Earthquakes Following Moderate Mainshocks (or, Why California Is Not Falling into the Ocean)

“…Hough (2001) and Hough et al (2003) presented evidence that remotely triggered earthquakes occurred during both the 1811-1812 New Madrid earthquake sequence and the 1886 Charleston, South Carolina earthquake. One of the supposed New Madrid mainshocks may in fact have been a triggered earthquake in the Wabash Valley (Mueller et al, 2004).…”

“…This period represents a compromise between the need to have sufficient data to resolve seismicity fluctuations and the desire to focus on events that might be associated with a given mainshock. The simplest explanation for delayed triggering is that transient stress changes cause very early triggered events, either large or small, and these initial triggered events cause local disturbances that generate subsequent local sequences (Hough and Kanamori, 2002;Hough et al, 2003). This hypothesis implies that immediate triggering occurs in locations where delayed triggering occurs.…”

Cataloging the 1811-1812 New Madrid, Central U.S., Earthquake Sequence

“…One immediate complication, in particular for analyzing events for which only a few accounts are available, is that one cannot assume that all of the events occurred in the New Madrid region. That is, Hough (2001) and Hough et al (2003) conclude that the 1811-1812 sequence included remotely triggered earthquakes, including at least three moderate events in the Louisville, Kentucky, region. More recently, several studies have concluded that remote triggering occurs pervasively in diverse tectonic settings (Hough 2005;Hough 2007;Velasco et al 2008).…”