A High-resolution 3-dimension Compositional Model of S. California and Its Implications on Crustal Strength

Abstract:

As one of the most seismically dynamic regions of the continental US, S. California also has complex tectonic history and geological environment, resulting in a mosaic of crustal blocks for which their strength varies significantly across the region. To better quantify one of the most important factors that determine the crustal strength, chemical composition of the crust, we construct a new map of crustal Vp/Vs by applying a newly-developed data processing scheme that involves a 2-layer H-k stacking technique. The resulting Vp/Vs map, after incorporating the shear velocity (Vs) determined by local arrays, is then translated into the silica content using an empirical relationship between seismic properties and petrology. In this presentation, we show that a regional high-resolution 3-dimension silica content model for the crust of the S. California is thus constructed with meaningful error estimations. This model provides unique insights into the geological and thermal properties in Southern California, as well as helps determine the strength of the crust in that quantification of silica content provides an assessment to the existence of quartz, one of the weakest minerals in the crust. Finally, we present an initial crustal strength model based on the compositional information revealed by the seismic structures and highlight variations within the model and their implications to the seismic activities of S. California.