ALBERT

Description: The ability to confidently estimate the depths of small-to-medium sized (3.5 ≤ m b  ≤ 5.5) seismic disturbances is important both in plate tectonics studies, and when monitoring compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Seismic source depths can be determined by identification of the teleseismic depth phases pP and sP , and also by modelling surface wave amplitude spectra. The radiation pattern of the teleseismic depth phase pP and fundamental mode Rayleigh amplitudes show that the effectiveness of these methods of earthquake depth estimation is dependent on the orientation of the focal mechanism and the station locations. For some focal mechanisms, the predicted amplitude of the teleseismic depth phase pP will only be large for stations in certain locations, and the Rayleigh wave spectral nulls that tightly constrain the seismic source depth when modelling surface wave amplitude spectra often only occur for a limited range of azimuths. In this study, we show that for sources where Rayleigh wave spectral nulls are not observed and the source depth cannot be constrained using the surface wave amplitude spectra, the focal mechanism obtained by modelling Rayleigh and Love wave amplitude spectra can be used to identify the locations of stations where pP should have a large amplitude and hence be easiest for an analyst to identify. The increased global coverage of seismometer stations means that there is an increased likelihood that stations exist in the locations where the predicted amplitude of pP is large. As the identified depth phases are consistent with the focal mechanism this approach allows increased confidence to be placed in the identified depth phases and hence the estimated source depth. This approach could potentially be used with other methods of focal mechanism estimation provided that the method used to estimate the focal mechanism is independent of the source depth.