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Estimating earthquake location and magnitude from seismic intensity data

Bulletin of the Seismological Society of America

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Abstract

Analysis of Modified Mercalli intensity (MMI) observations for a training set of 22 California earthquakes suggests a strategy for bounding the epicentral region and moment magnitude M from MMI observations only. We define an intensity magnitude MI that is calibrated to be equal in the mean to M. MI = mean (Mi), where Mi = (MMIi + 3.29 + 0.0206 * ??i)/1.68 and ??i is the epicentral distance (km) of observation MMIi. The epicentral region is bounded by contours of rms [MI] = rms (MI - Mi) - rms0 (MI - Mi-), where rms is the root mean square, rms0 (MI - Mi) is the minimum rms over a grid of assumed epicenters, and empirical site corrections and a distance weighting function are used. Empirical contour values for bounding the epicenter location and empirical bounds for M estimated from MI appropriate for different levels of confidence and different quantities of intensity observations are tabulated. The epicentral region bounds and MI obtained for an independent test set of western California earthquakes are consistent with the instrumental epicenters and moment magnitudes of these earthquakes. The analysis strategy is particularly appropriate for the evaluation of pre-1900 earthquakes for which the only available data are a sparse set of intensity observations.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Estimating earthquake location and magnitude from seismic intensity data
Series title:
Bulletin of the Seismological Society of America
Volume
87
Issue:
6
Year Published:
1997
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Bulletin of the Seismological Society of America
First page:
1502
Last page:
1521