[S13-P] Poster

[S13-P-02] Centroid moment tensor solution using 3D heterogeneous anisotropic Earth: application to Papua New Guinea and Solomon Islands

^○Babak Hejrani¹, Hrvoje Tkalcic¹, Andreas Fichtner² (1.The Australian National University, Research School of Earth Sciences, ACT, Australia, 2.ETH Zurich, Zurich, Switzerland)

Moment tensor (MT) representation of the earthquake source is well established and is being routinely calculated on a global scale by Global-centroid moment tensor project (GCMT). Routine calculation of MT is usually done using Green's functions calculated from a 1D layered Earth velocity structure. Here, we have calculated CMTs for 318 events with Mw > 5.0 occurred in Papua New Guinea and Solomon Islands during 2006 - 2016 using a continental scale 3D heterogeneous upper-mantle velocity structure model, AMSAN19 (Fichtner et al. 2009). Our solutions show considerable differences in comparison to GCMT. The most prominent difference is in double-couple (DC) percentage which shows a significant increase. We also observe differences in strike, dip and rake angles of the DC part of MT, which provides new insight into the tectonics of the region. The resolution in centroid depth has increased specifically for shallow events (depth < 25 km) and our new centroids shed light on dipping structures at the New Guinea Trench. The new CMT solutions obtained using the 3D model are superior to those using the spherically-symmetric models of the Earth, which is evident in the data fit increase of about 30%.
We have shown the feasibility of using a 3D velocity model on the continental scale to improve the recovery of depth, location and MT components for shallow events, which opens new avenues to more reliable tectonic interpretations and hazard assessments. Our library of synthetic seismograms will be used at Geoscience Australia to supplement existing tools for moment tensor inversion.

Reference:
Fichtner, A., Kennett, B.L.N., Igel, H. & Bunge, H.-P., 2009. Full seismic waveform tomography for upper-mantle structure in the Australasian region using adjoint methods, Geophys. J. Int., 179, 1703–1725.