Body wave moment tensor inversion of local earthquakes: an application to the South Iceland Seismic Zone

• Published in: Geophysical Journal International
• Main Authors: Hossein Shomali, Z., Slunga, Ragnar
• Format: Text
• Language: English
• Published: Oxford University Press 2000
• Subjects: Articles; Iceland
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/140/1/63; https://doi.org/10.1046/j.1365-246x.2000.00989.x

The focal mechanisms and scalar seismic moments of four local earthquakes are determined using a seismic moment inversion method for frequencies larger than those of dominant oceanic noise and lower than the corner frequency. The earthquakes have epicentral distances ranging from 9 to 42 km and were recorded by the South Iceland Lowland (SIL) seismic network. Synthetic seismograms are computed using the frequency–wavenumber integration technique for an elastic horizontally layered medium. Moment tensor inversion is then carried out using windows designed around P and S waveforms on individual components and at individual seismic stations. The waveforms within each window are then inverted in the time domain simultaneously on all components and at all available seismic stations. The trace elements of the seismic moment tensor are subject to the deviatoric constraint (zero trace element). The results of the inversion are classified as a sum of double couple and CLVD sources, and then compared with the results from the automatic amplitude spectra method routinely used in the SIL network. The comparison shows fairly good agreement between the two approaches, considering that the former uses both amplitude and phase information and the latter uses only amplitude information. The first three events studied have moment magnitudes in the range 2.3 ≤ M w ≤ 3.1 and comprise two foreshocks and an associated main shock. The weighted least squares inversions for these events show dominant strike slip faulting with scalar seismic moments of the order of 0.285 × 1013 ≤ M 0 ≤ 4.966 × 1013 N m. The fourth event is characterized by a moment magnitude M w = 2.2 and scalar seismic moment M 0 = 0.243 × 1013 N m. This event also shows a significant strike slip component.