Publication Date:
2013-02-07
Description:
In this study, we establish the empirical relationships between the spatial dimensions of the aftershock zones and moment magnitudes ( M w ) for the Taiwan region. The length ( l ) and width ( w ) of the aftershock zone of an earthquake is measured by the major and minor axes, respectively, of the ellipse of a two-dimensional Gaussian distribution of one-day aftershocks. Our data is composed of 649 mainshocks (depth≤70 km, M w 4.0–7.6) between 1990 and 2011. The relationships between aftershock zone dimensions and M w were obtained by least-squares method with the corresponding uncertainties estimated by bootstrap. Our study confirms that aftershock zone dimensions are independent of faulting types and the seismic moment is proportional to l 3 . The ratio ( w / l ) increases slightly with M w and is independent of faulting types. Together with previous study, our results suggest that earthquakes of both small ( M w =4.0) and large ( M w ≥7.0) magnitudes have similar focal zone geometrical parameters. By using the M w – S relation, where the aftershock zone area S is estimated from l and w , we also provide an independent examination of the variations in the median stress drop. We find that the median stress drops of strike-slip earthquakes are higher than those of thrust events. Moreover, the median stress drops are independent of the moment magnitudes for normal and strike-slip events but decrease for large thrust events. These results are consistent with the latest global observations. Regardless of faulting types, the median stress drop decreases for larger (6≤ M w ≤7.6) and relatively deep (depth~60–70 km) earthquakes. Online Material: Effect of up-dip rupture propagation on estimated maximum slip duration, details on teleseismic and geodetic stations, and figures of far-field displacements, temporal change in slip, and snapshots of the semblance-value distribution.
Print ISSN:
0037-1106
Electronic ISSN:
1943-3573
Topics:
Geosciences
,
Physics
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