Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by SINGH, S. K. Articles by SUÁREZ, G. Search for Related Content GeoRef GeoRef Citation

Regional variation in the number of aftershocks (m_b 5) of large, subduction-zone earthquakes (M_w 7.0)

INSTITUTO DE GEOFISCIA UNIVERSIDAD NACIONAL AUTONOMA DE MEXICO, 04510 MEXICO, D.F. Mexico

Abstract

It is reasonable to expect that the number of aftershocks following a large earthquake should reflect the degree of heterogeneity on and near the fault plane. To investigate this question, we plot N, the number of aftershocks with m_b 5.0 occurring within the next 30 days after large, subduction-zone, thrust-faulting earthquakes (M_w 7.0), versus the magnitude (M_w) of the main shock. Only earthquakes that occurred after the installation of the World-Wide Standard Seismographic Network stations are considered. Because the detection threshold of aftershocks in many regions is greater than m_b = 5.0, N is obtained by fitting the data to Gutenberg and Richter's relation (log N = a – b · m_b). For the same M_w, N varies by a factor of about 40 in different regions. N is less than expected in the eastern Pacific (including Alaska) and is greater than expected in the western Pacific. Relative lack and excess of N correlates well with regions of supposedly strong and weak coupling, respectively. While small and large N also show some correlation with the expansion rate of aftershock area with time, the variation in N is much larger than would be expected from the mere increase of aftershock areas. In some cases, it appears that the number of aftershocks, N, for earthquakes of similar M_w, may also reflect the complexity and enrichment of the P-wave amplitude spectra from 1 to 10 sec. For example, the Valparaiso, Chile, earthquake of 1985 (M_w = 8.0) generated N = 46 earthquakes, whereas for the Michoacán, Mexico, event of 1985 (M_w = 8.1), N is only equal to 5. Furthermore, for the Valparaiso earthquake, P waveforms are much more complex, and the spectra are more energetic at 1 to 10 sec as compared to the 1985 Michoacán event.

This article has been cited by other articles:

				Strongly Depth-Dependent Aftershock Production in Deep Earthquakes Bulletin of the Seismological Society of America, October 1, 2004; 94(5): 1808 - 1816.

				F. Courboulex, M. A. Santoyo, J. F. Pacheco, and S. K. Singh The 14 September 1995 (M = 7.3) Copala, Mexico, earthquake: A source study using teleseismic, regional, and local data Bulletin of the Seismological Society of America, August 1, 1997; 87(4): 999 - 1010. [Abstract] [PDF]

				S. K. SINGH, D. COMTE, and M. PARDO Background seismicity and strength of coupling in the subduction zones Bulletin of the Seismological Society of America, October 1, 1992; 82(5): 2114 - 2125. [Abstract] [PDF]