Paleoseismicity: Seismicity Evidence for Past Large Earthquakes

Abstract

Clusters of earthquakes in continental intraplate regions are used to estimate the times and magnitudes of past earthquakes in a model we call "paleoseismicity." The time of a past earthquake is estimated from an Omori-law decay of the aftershocks with time, while the magnitude of the earthquake is inferred from the length of the current zone of seismic activity. The observed aftershocks of several intraplate earthquakes are used to find the parameters describing the Omorilaw aftershock decay, and these parameters are found to fall in the same range as those for aftershock sequences from California. The paleoseismicity model is shown to be approximately consistent with the current seismicity rates at the New Madrid, Missouri; Charleston, South Carolina; and Charlevoix, Qudbec seismic zones. Near Basel in Switzerland, the paleoseismicity model is consistent with the occurrence of the large earthquake there in 1356. However, at ArdennesHautes Fagnes, Belgium; Hainaut, Belgium; and Bree, Belgium the paleoseismicity model either underestimates the rate of current seismicity or suggests earthquakes not known in the historic record. The paleoseismicity model may be most applicable to low-strain-rate, intraplate regions where aftershock rates above the background seismicity level can persist for very long periods of time. If many current small earthquakes are aftershocks of past large events, then it may not be appropriate to use earthquake rates from recent seismicity to calculate the seismic hazard in probabilistic analyses.

Wagon Loads of Sand Blows in White County, Illinois

“…Using a model incorporating rate-and-state friction, Dieterich (1994) shows that the rate of aftershocks divided by the background seismicity rate is proportional to the mainshock stressing rate normalized by the long-term stress rate. This model is consistent with the observation that long-lived aftershock sequences are relatively common in intraplate regions (Ebel et al, 2000), as intraplate earthquakes are generally thought to be associated with high stress-drop values (Scholz et al, 1986) as well as low background stressing rates. As Stein and Newman (2004) showed, quantitative estimates of aftershock duration in low-strain-rate regions depend critically on parameters that are difficult to determine with precision, but with plausible choices of parameters for the New Madrid sequence, the method of Dieterich (1994) does predict sequences that last for several hundred years.…”

Megathrust and accretionary wedge properties and behaviour in the Makran subduction zone

“…These events may be late-stage aftershocks of the 1945 earthquake, as aftershock sequences have been known to continue for decades or even centuries after the mainshock (Ebel et al, 2000). Taking the fault planes of the shallow thrust earthquakes to be the northward-dipping nodal planes, most have dips of 8-10…”

Spatial Variability of "Did You Feel It?" Intensity Data: Insights into Sampling Biases in Historical Earthquake Intensity Distributions

“…This event has been interpreted by some studies as a late, large aftershock of the 1811-1812 New Madrid sequence (e.g., Ebel et al, 2000;Stein and Liu, 2009), although the interpretation for a long-lived aftershock sequence has recently been called into question (Page et al, 2012). Whether or not the 1843 event is an aftershock, it was widely felt throughout the region and emerges as an important event for assessing seismic hazard.…”