Rupture Process of the 2014 Iquique Earthquake Estimated from Tsunami Waveform and GPS Data

Abstract:

A great earthquake (Mw 8.2) occurred on April 1, 2014 at 23:46:46 off the coast of Iquique, Chile (USGS). The earthquake generated a tsunami that was recorded at four DART buoy and seven tide gauge stations. The tsunami amplitudes recorded at two closest tide gauge stations from the epicenter (Pisagua and Iquique) are both 187 cm. A GPS station in Iquique located about 98 km SE of the epicenter recorded the co-seismic displacement caused by the earthquake. The recorded horizontal and vertical displacements are -28.90(± 0.16) cm E, 3.90(± 0.12) cm N, and -3.80(± 0.60) cm Z. We use tsunami waveforms and co-seismic displacement data in a joint inversion to estimate the slip distribution of the 2014 Iquique earthquake. We apply a multiple time window inversion to show the spatial and temporal slip distribution. The fault geometry that we use is based on the SLAB1.0 model and aftershock depths. The fault geometry resembles the curvature of SLAB1.0 but with shallower depth; strike angle of 347°, rake angle of 90°, and sub-fault size of 20 km × 20 km are used. By assuming the rigidity of 4 × 10¹⁰ N/m², the seismic moment for the 2014 Iquique earthquake calculated from the estimated slip distribution is 1.04 × 10²¹ Nm, which is equivalent to Mw 8.0. The dimension of major slip region of the slip distribution is 80 km × 40 km, and the maximum slip amount is 7.06 m. The major slip region is located down dip of the hypocenter and the rupture propagates from the epicenter to the SE direction. Instead of an instantaneous rupture process, the use of a more realistic rupture velocity (2.0, 2.8, or 3.0 km/s) can better explain the tsunami data. The selection among these three realistic rupture velocities does not strongly affect the estimated slip distribution. We also estimate the slip distribution using three other fault geometries, two of which have the same curvature as our final model but with different depths, and the third has a single dip angle. Our final slip distribution gives simulated tsunami waveforms and calculated co-seismic displacements that are slightly closer to the observations compared to those that used other fault geometries. Deeper fault geometries give larger total seismic moment, and the precise slip amount on each sub-fault is strongly dependent on the assumed fault geometry.