Systematic analysis of deep seismicity: 200 centroid‐moment tensor solutions for earthquakes between 1977 and 1980

Abstract

A systematic study of deep seismicity is performed using wave‐form data from the GDSN between 1977 and 1980 and the Centroid Moment Tensor method of Dziewonski et al. Two hundred new CMT solutions are found for events deeper than 100km; their moments, obtained using the same algorithm, range between 7 × 1023 and 1.4 × 1028 dyne cm ‐ a factor of 20 000. A statistical analysis of the CMT parameters provides important conclusions. Among these, the shift in origin time for deep events is found to be almost independent of the seismic moment, providing an indication of the complexity of deep earthquakes. The deviation from the double couple model appears to be correlated to the state of stress of the subducting slabs; mechanisms showing down‐dip compression are generally dominated by the eigenvalue corresponding to the compression axis, and down‐dip tension correlates with the predominance of the tensional eigenvalue. Comparison with moment tensors obtained by other authors using different waveform data shows good agreement between different methods. Comparison with published focal plane mechanisms confirms the precision and reliability of the CMT method. Examples of CMT solutions used to identify patterns of seismicity associated with deep fault planes are shown. Copyright © 1984, Wiley Blackwell. All rights reserved