Regional Dependence of Strong Ground Motion in the Chilean Subduction Zone

Ground motion prediction models (GMPM) are essential for probabilistic seismic hazard analyses. We developed a GMPM for spectral accelerations up to a period of 10 s for the central zone of Chile, specifically for the region from Los Vilos to San Antonio (latitudes -32 degrees to -33.77 degrees), the busiest industrial area in the country. For the development of the model, seismic data published by the National Seismological Center (CSN) were added to a published database for the Chilean strong ground motions. New measurements of the average shear-wave velocity for the upper 30 m (Vs30) made at stations in the segment are included. Orientation-independent intensities are computed, reducing epistemic uncertainty in the model development phase. The developed model is a better fit to the seismic intensities for central Chile than global and national models, with lower total standard deviation at the expense of a constraint area of applicability. The importance of studying the seismic segmentation in the Chilean subduction zone is emphasized when observing different behaviors depending on the latitude or the segment along the margin. We developed similar GMPMs for the area north of -32 degrees and south of -33.7 degrees using the original database. For the same subduction zone, there is a heterogeneity in the source characteristics, which generates different maximum earthquake sizes, slab slopes, and wave paths, all of which cause different seismic intensities. This observation should lead, in the future, to the development of zone-dependent seismic design codes, which means an advance in seismic hazard preparedness.