Moment tensor inversion of local earthquake data—II. Application to aftershocks of the May 1980 Mammoth Lakes earthquakes

Abstract

Near‐source data were collected by the USGS from the Mammoth Lakes earthquakes aftershock sequence in May/June 1980. This data set was used to perform moment tensor inversions for events where recordings existed at more than 10 stations. Since 1‐D reflectivity modelling was used for calculating the appropriate Green's functions, the 10 station constraint was imposed to try to minimize the influence of complex structure in the vicinity of Long Valley caldera. Due to these constraints only relatively strong events in the magnitude range 3.5 ≤ML≤ 4.5 were studied. The moment tensors from the inversions indicate that in almost all cases only the m2 or (M12) component was significantly excited. This type of moment tensor corresponds to a pure vertical strike–slip mechanism striking north with left‐lateral movement. This result is in good agreement with results by Lide & Ryall (1985), who found hypocentre lineations for the aftershocks on N–S extending zones. They are also similar to the mechanisms initially proposed for the four ML= 6 mainshocks by other investigators as well as consistent with the composite fault plane solution of Archuleta et al. (1982) and cannot be interpreted in terms of a CLVD mechanism for dike injection. Copyright © 1991, Wiley Blackwell. All rights reserved