Source Parameters of Earthquakes in Eastern and Western North America Based on Finite-Fault Modeling

Abstract

The ground motion from large earthquakes is often predicted based on finite-fault modeling, in which the fault plane is discretized into small independently rupturing subfaults; the radiation from all subfaults is summed at the observation point. Despite the success of the method in matching observed ground-motion characteristics, the physical interpretation of the subfaults has remained largely unclear, and a rationale for the choice of the subfault attributes has been lacking. Two key parameters-the subfault size and the maximum slip velocity on the fault-govern the amplitude of the source spectrum at intermediate and high frequencies, respectively. We determined these key source parameters, on an event-by-event basis, for all well-recorded moderate to large earthquakes in western North America (WNA) by fitting simulated to observed response spectra. We compare the values of these source parameters with those obtained previously for eastern North America (ENA) and the Michoacan, Mexico, earthquakes (a total of 26 modeled events).We find that the characteristic subevent size increases linearly with moment magnitude in an apparently deterministic manner. The subevent size relationship obtained for WNA is not statistically different from that obtained for ENA. In both regions, the subevent size follows the trend of log Dl ‫ס‬ ‫2מ‬ ‫ם‬ 0.4 M (4 Յ M Յ 8), where Dl is the subfault size in km. This trend agrees well with independent studies by Somerville et al. (1999) and Aki (1992), in which the characteristic size of the patches ("asperities" or "barriers") on earthquake faults was determined. These results indicate that large earthquakes should be viewed as a sequence of smaller events that comprise the large rupture. Interestingly, the characteristic size of these constituent small events appears to be directly related to the size of the overall rupture.The slip velocities determined for all 26 earthquakes vary in a narrow range from about 0.25 to 0.60 m/sec, with a mean of 0.40 m/sec and standard deviation of 0.09 m/sec. The slip velocities for the ENA events are distributed randomly over this range, while those for the WNA region appear to exhibit a decreasing trend with increasing magnitude. Our results indicate that a generic, region-independent earthquake source model for engineering prediction of strong ground motions can be developed.

Broadband NDSHA computations and earthquake ground motion observations for the Italian territory

“…The lower corner frequency f C1 is related to fault dimensions or rupture duration, whereas the physical meaning of the second corner frequency f C2 is not so clear. Papageorgiou and Aki (1983) and later Beresnev and Atkinson (2002) relate f C2 to the characteristic size of an assumed crack-like subsource, whereas Gusev (2013) believes that it is related to the local rise time, T R , and to the slip-pulse width l. In the following, the main notion is the rms average acceleration source spectrum…”

“…For Japan, the absolute level is log 10 A HF (M w = 7) = 26.22 after Irikura and Miyake (2011). However, many authors (Toro et al, 1997;Beresnev and Atkinson, 2002;Halldorsson and Papageorgiou, 2005) identified scaling behaviour of AHF that violates similarity. All of them found slower increase of A HF vs. M 0 as compared to (4).…”

“…All of them found slower increase of A HF vs. M 0 as compared to (4). Beresnev and Atkinson (2002), on the basis of mean trends derived from the WUSA dataset, found that the effective Δσ for a point-source B70 model may drop from about 150 bars, for M w = 5, to (extrapolated) 25 bars for M w = 8. In other words, effective Δσ or 'stress parameter' decreases with decreasing M w .…”

Broadband NDSHA computations and earthquake ground motion observations for the Italian territory

“…For Japan, the absolute level is log 10 A HF (M w = 7) = 26.22 after Irikura and Miyake (2011). However, many authors (Toro et al, 1997;Beresnev and Atkinson, 2002;Halldorsson and Papageorgiou, 2005) identified scaling behaviour of AHF that violates similarity. All of them found slower increase of A HF vs. M 0 as compared to (4).…”

Heterogeneous Slip Distribution Self-Similarity on a Fault Surface

“…Okubo and Aki 1987;Lee and Schwarcz 1995). The self-similarity of earthquake slip distributions is an essential physical characteristic of earthquake kinematics and was discussed in previous studies (Beresnev and Atkinson 2002;Manighetti et al 2005Manighetti et al , 2007Wesnousky 2008;Klinger 2010). Wesnousky (2008) analyzed earthquake rupture traces and coseismic surface slip and obtained the scaling relationship between the slip and rupture length for strike-slip earthquakes.…”