Source Parameters of the Mw 5.7 Pica Crustal Earthquake in Northern Chile

On 10 September, 2008, an M-w 5.7 earthquake occurred under the Central Valley of northern Chile near the town of Pica at a depth of similar to 33 km within the continental crust of the South America plate. We find this earthquake to be a high stress-drop, reverseoblique event that generated unusually high ground accelerations of up to 0.67g. Overall, its observed ground motion intensities are considerably larger than those predicted by ground motion models, particularly at short periods. The source properties inferred through waveform modeling indicate reverse-oblique fault motion on a similar to 75 km(2) plane dipping to the northeast, which is corroborated by the located aftershock distribution. Stress-drop values of the mainshock and larger aftershocks were estimated through S-wave spectrum modeling, with values up to similar to 250 MPa for the mainshock. The event occurred in a cold section of the continental crust under the Central Valley, and its fault kinematics and orientation are consistent with the dominant style of faulting and stress field under the neighboring Coastal Cordillera. Although our recurrence analysis shows that crustal events in the region occur at a lower rate than interplate and inslab events, crustal events of similar or higher magnitude than the Pica earthquake have occurred, on average, approximately once every three years in northern Chile, which could pose an important hazard to nearby populations or critical infrastructure.

Automated summary

On September 10, 2008, a M-w 5.7 earthquake occurred in the Central Valley of northern Chile near the town of Pica. The earthquake had a high stress-drop and generated unusually high ground accelerations. The source properties indicate reverse-oblique fault motion on a plane dipping to the northeast, consistent with the dominant style of faulting in the region. Despite the lower occurrence rate of crustal events compared to interplate and inslab events, similar or larger magnitude crustal events have occurred approximately once every three years in northern Chile, posing a significant hazard to nearby populations or critical infrastructure.