Comparative evaluation of tsunami-GPS and teleseismic body wave inversion methods for the 2014 Iquique, Chile, earthquake

Aditya Riadi Gusman, #Satoko Murotani, Kenji Satake, Mohammad Heidarzadeh, Shingo Watada (ERI, Univ. Tokyo), Endra Gunawan (Nagoya Univ.), and Bernd Schurr (GFZ)

Seismological Society of Japan Meeting, Niigata, Japan, 24-26 November 2014.

1. Introduction
Tsunami waveforms, land based GPS data and teleseismic body waves respectively provide good estimate on spatial slip distribution of submarine earthquake, static slip distribution beneath land, and the precise timing of slip history. Here we compare the slip distributions of the April 1, 2014 Iquique earthquake (Mw 8.2: USGS) from teleseismic inversion and a joint inversion of tsunami waveforms and GPS data.

2. Data and methodology
We used tsunami waveforms recorded at DART buoys across the Pacific Ocean and near-field tide gauges, and co-seismic displacements recorded by northern Chile GPS networks in the joint multi-window inversion to estimate the spatial and temporal slip distribution. In constructing the tsunami Green’s function we consider the effects of the elastic loading of the seafloor by the tsunami, the density variation of the compressible seawater, and the geopotential variation due to the movement of water mass on the linear long-waves (Watada et al., 2014: JGR), which gives the ability to use far-field tsunami waveforms in the inversion.
For the teleseismic waveforms, we inverted 54 P-wave vertical components and 1 SH-wave horizontal component using the method of Kikuchi and Kanamori (1991: BSSA) based on the same fault geometry of the tsunami and GPS data joint inversion.
Rupture durations of 45 s and 44 s on each subfault are assumed for the joint inversion and teleseismic inversion, respectively. To evaluate the sensitivity of rupture velocity to the estimation of slip distribution, we used different rupture velocities.

3. Estimated rupture processes
The teleseismic inversion with different rupture velocities yielded similar moment rate functions (Fig.b) but their spatial slip distributions are different. On the contrary, the joint inversion gives a stable spatial slip distribution (Fig.a) for different rupture velocities. Tsunami waveforms do not have the resolution in determining precise rupture history; therefore, the maximum rupture duration has to be guided by the moment rate function estimated from teleseismic inversion. When the same duration is assumed, the total seismic moment estimated by the teleseismic inversion (2.33 × 1021 Nm, Mw 8.2) is larger than that from the joint inversion (1.20 × 1021 Nm, Mw 8.0).
Fig. a) Slip distribution of the 2014 Iquique earthquake estimated from tsunami waveform and GPS data. b) Moment rate functions from teleseismic body waves using different rupture velocities. c) Moment rate functions from tsunami waveforms and GPS data using different rupture velocities.

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