Comparative study of two tsunamigenic earthquakes in the Solomon Islands: 2015 M-w 7.0 normal-fault and 2013 Santa Cruz M-w 8.0 megathrust earthquakes

摘要

The July 2015 M-w 7.0 Solomon Islands tsunamigenic earthquake occurred similar to 40 km north of the February 2013 M-w 8.0 Santa Cruz earthquake. The proximity of the two epicenters provided unique opportunities for a comparative study of their source mechanisms and tsunami generation. The 2013 earthquake was an interplate event having a thrust focal mechanism at a depth of 30 km while the 2015 event was a normal-fault earthquake occurring at a shallow depth of 10 km in the overriding Pacific Plate. A combined use of tsunami and teleseismic data from the 2015 event revealed the north dipping fault plane and a rupture velocity of 3.6 km/s. Stress transfer analysis revealed that the 2015 earthquake occurred in a region with increased Coulomb stress following the 2013 earthquake. Spectral deconvolution, assuming the 2015 tsunami as empirical Green's function, indicated the source periods of the 2013 Santa Cruz tsunami as 10 and 22 min.