Giuliano Sant’Anna Marotta

Strains arising by seismic events in the SIRGAS-CON network region

Abstract In this study, we investigate surface strains related to seismic events and their relationship with pre- and post-seismic events in Latin America, by analyzing the variation of estimated earth coordinates supplied by a geodetic network called SIRGAS-CON. Based on data provided by the USGS for the period 2000-2011, and after the Global Congruency test, we selected four events associated with unstable geodetic network points. The resulting strains were estimated based on the finite element method using networks of points considered unstable connected to neighboring points using the Delaunay triangulation. It was possible to determine the strains along with the resulting guidelines for pre- and post-seismic, considering each triangular lattice formed for analysis as a homogeneous solid body. The calculation of strains and verification of the results allowed to analyze the interactions between lithospheric plates from the contraction and extension directions between points located in different plates. Despite the association between seismic events and the strain of geodetic network, some events of magnitude greater than 5.8 Mw were excluded because it does not show (provide) 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.

Calibration of the local magnitude scale (M L ) for Peru

We propose a local magnitude scale (ML) for Peru, based on the original Richter definition, using 210 seismic events between 2011 and 2014, recorded by 35 broadband stations of the National Seismic Network operated by the Geophysical Institute of Peru. In the solution model, we considered 1057 traces of maximum amplitude records on the vertical channel from simulated Wood-Anderson seismograms of shallow events (depths between 0 and 60 km) and hypocentral distances less than 600 km. The attenuation factor has been evaluated in terms of geometrical spreading and anelastic attenuation coefficients. The magnitude ML was defined as ML = Log10AWA+1.5855Log10(R/100)+0.0008(R−100)+3±S, where, AWA is the displacement amplitude in millimeters (Wood-Anderson), R is the hypocentral distance (km), and S is the station correction. The results obtained for ML have good correlation with the mb, Ms and Mw values reported the ISC and NEIC. The anelastic attenuation curve obtained has a similar behavior to that other highly seismic regions. Station corrections were determined for all stations during the regression analysis resulting in values ranging between −0.97 and +0.73, suggesting a strong influence of local site effects on amplitude.