Strain Rate by Geodetic Observations Associated with Seismic Events in the SIRGAS-CON Network Region.

Abstract:

This research investigates surface strains related to seismic events and their relationship with pre- and post-seismic events in South American, Antarctica, Nazca, Cocos, North American and Caribbean plates , by analyzing the variation of estimated earth coordinates, for the period 2000-2014, supplied by a geodetic network called SIRGAS-CON. Based on data provided by the USGS for the same period, and after the Global Congruency test, we selected the events associated with unstable geodetic network points. The resulting strains were estimated based on the finite element method. It was possible to determine the strains along with the resulting guidelines for pre- and post-seismic, considering each region formed for analysis as a homogeneous solid body. Later, a multi-year solution of the network was estimated and used to estimate the strain rates of the earth surface from the changing directions of the velocity vectors of 332 geodetic points located in the South American plate and surround plates. The strain rate was determined and, using Euler vector computed, it was possible to estimate the convergence and accommodation rates to each plate. The results showed that contraction regions coincide with locations with most of the high magnitude seismic events. It suggest that major movements detected on the surface occur in regions with more heterogeneous geological structures and multiple rupture events; significant amounts of elastic strain can be accumulated on geological structures away from the plate boundary faults; and, behavior of contractions and extensions is similar to what has been found in seismological studies. Despite the association between seismic events and the strain of geodetic network, some events of high magnitude were excluded because it does not show the surface strain, which is located at great depths. It was confirmed that events of greater magnitude provide increased surface strain rate when compared with other similar depths.