SOURCE PROPERTIES OF THE JULY 19 2014 MW 7.4 INTRASLAB NORMAL FAULTING EARTHQUAKE OCCURRED NEAR SAN PEDRO DE ATACAMA, CHILE
In July 19, 2024, a large intraplate normal fault earthquake Mw 7.4 occurred with epicenter near San Pedro de Atacama, Chile. The United States Geological Survey (USGS) located the event at 127 km depth, with epicenter at 23.08°S, and 67.84°W. Seismological agencies determined the centroid moment tensor (CMT) using long period waves. A large non-double-component (NDC) is systematically observed. For instance, the USGS gives 31%, and the Global CMT 41%. The nodal planes (NPs) from W-phase CMT solution are, NP1: 172°/21°/-80° and NP2: 341°/69°/-94°, for strike/dip/rake, respectively; while the scalar seismic moment is M0=1.44×1020 N.m (Mw 7.37), and half-duration of 12.5 s. The solution from teleseismic body-waves determined by the USGS shows a similar steep nodal plane with a dip=71° and strike=346°, compared with the W-phase solution. We analyzed the source properties of the main shock using long period waves and we used the W-phase method to compute the CMT. The goal is to determine the causative fault and investigate the kinematic rupture using near-field and teleseismic body waves. We extract teleseismic body waves (P- and SH-waves) from broadband stations with epicentral distances between 30° and 90°. Near-field recordings were also analyzed using stations with epicenter distances up to 250 km. Starting from the best double-couple solution determined by the USGS using body-waves, we slightly adjusted the strike and dip of NP2 to be consistent with observed P-waves polarities, in order to set the fault geometry. Then, for each nodal plane we computed a kinematic rupture model for the 2024 Mw 7.4 San Pedro de Atacama earthquake from the joint inversion of teleseismic body waves and near-field data. Preliminary results show that the solution for the NP2 presents better fitting between synthetics and observed waveforms. The slip is distributed over an area of ∼60 × 75 km2, with a maximum slip of ~0.7 m with a rupture propagating downward from the hypocenter. Instead, for NP1 the rupture covers a similar area of ∼65 × 65 km2, with a maximum slip of ~0.75 m, and a rupture propagating mainly southward from the assumed nucleation point. The large non double-couple component of the event suggests that there is more complexity than the pure shear dislocation assumed in the finite-source analysis done in this work.