163-G 2.1

Spatiotemporal characteristics of paleo-, historic and recent earthquakes in the broken foreland of the south-central Andes

In this project we will investigate large and medium-magnitude earthquakes using waveform analysis of historical and modern seismograms for event location, magnitude, and depth as well as focal mechanisms and source-time function. Historical earthquakes recorded at analog stations worldwide (primarily recorded on paper or film) since the beginning of the last century can be digitized and analyzed with advanced methods to better constrain their characteristics. For example, using waveform inversion, we are able to derive depth, lateral extent, and the true fault plane as well as zones of increased slip along rupture planes. With such a data set, we aim to identify and quantify the related earthquake surface-rupture trace or remnants of earlier surface ruptures in the epicentral regions. High-resolution satellite imagery, aerial photography, cosmogenic nuclide exposure dating of offset geomorphic markers, fault scarp measurements, and fault trenching will complement this analysis and provide an unprecedented data set to assess earthquake characteristics. We will focus on the large magnitude, shallow crustal seismic events in the region in the Andean foreland, e.g., the 1894 (M8), 1908 (M6.8), 1929 (M6.5), 1944 (M7.8), 1952 (M7.0) and 1977 (M7.4) events. Depending on the quality of historic records and local conditions, we will select two sites (preferably the 1894 and 1952/1977 San Juan events). For these sites, we will relocate medium-size earthquakes, determine their seismic moment tensors (focal mechanisms) and depth from waveform inversion and thereby test possible relationships between recent seismic activity and surficial deformation characteristics. Deployment of temporary seismic stations in addition to existing permanent stations at one or two selected sites will help identify active structures from small magnitude events. We will reevaluate seismic-moment tensors for the foreland region for recent events, where the magnitude threshold depends on data availability. Taken together, the results will provide better insight into the relationships between aseismic and seismic deformation, the identification of active structures, and possible changes in the spatiotemporal deformation characteristics of important structures. Such knowledge will ultimately shed light on the dynamics of Quaternary tectonic activity compared to the overall tectonic and topographic evolution of ranges in the broken foreland and help elucidate the background sedimentation rates and patterns in light of tectonic forcing mechanisms.