New Relocated Seismicity Using an Improved Crustal Structure Model in the Eastern Sierras Pampeanas (29°S ? 32°S), Andean Retroarc of Argentina.

VENERDINI, AGOSTINA; ARAUJO,MARIO; BECK, SUSAN; AMMIRATI, JEAN-BAPTISTE; GILBERT, HERSH; ANDERSON, MEGAN; ALVARADO, PATRICIA; LINKIMER, LEPOLT

Miami, Florid

Congreso; Seismological Society of America ? Latin American and Caribbean Seismological Commission 2018; 2018

Seismological Society of America y Latin American and Caribbean Seismological Commission

We used seismic broadband records from the SIerras Pampeanas Experiment using a Multicomponent BRoadband Array and the Eastern Sierras Pampeanas array to analyze modern shallow seismicity using a new seismic velocity model for the continental crust of the Eastern Sierras Pampeanas (ESP). The ESP, located in the central part of Argentina, more than 700 km east from the trench, are the easternmost manifestation of crustal deformation in the Andean retroarco between 29and 32°S. We obtained a crustal velocity model using the joint inversion of teleseismic receiver functions and surface wave data, calibrated with gravity measurements. This model describes in detail the crustal seismic velocity variations beneath the ESP. Then, we analyzed crustal earthquakes recorded by the arrays that occurred during 2008?2010. An average of 49 P and S wave arrivals per event were picked and resulted in 31 new earthquake locations. Errors in location appeared to be improved with values on average of 1.2km in latitude,1.7km in longitude and 2.7 km in focal depth. The average rms is 0.27s and the average azimuthal gap is 104°. In addition, we determined first motion focal mechanisms further constrained with amplitude ratios SH/P, SV/P and SV/SH. Finally, we inverted these focal mechanism solutions to estimate the regional stress tensor. We observe that most of the analyzed seismicity beneath the ESP is located between 10 and 25km depths in the central part between 30.5?31.5°S. Our focal mechanisms are mainly reverse and consistent. These small to moderate size earthquakes should not be underestimated in this region of Argentina that concentrates 1.33 M inhabitants, one nuclear power plant, 12 large dams Historical and modern seismicity seem to agree with shallow focal depths, which enhance the seismic hazard in this region. Future work will include more seismicity and seismic sources, aftershocks and structure characterization.