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CHARGE 2000 - 2002

Using Broadband Data from the Passive Temporal IRIS-PASSCAL CHARGE Deployment to Study Crustal Earthquakes by Patricia Alvarado Department of Geosciences University of Arizona Universidad Nacional de San Juan, Argentina. CHARGE 2000 - 2002.

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CHARGE 2000 - 2002

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  1. Using Broadband Data from the Passive Temporal IRIS-PASSCAL CHARGE Deployment to Study Crustal Earthquakes by Patricia Alvarado Department of Geosciences University of Arizona Universidad Nacional de San Juan, Argentina CHARGE 2000 - 2002

  2. Areas of flat or shallow slab subduction around the world Flat slab subduction near 30°S possibly related to subduction of the Juan Fernandez Ridge ? How does crustal seismicity compare with major tectonic features (ex. JFR, Paleozoic terranes)?

  3. Historical Crustal Earthquakes Historical seismicity from INPRES (on-line catalogue) Larger sized and more frequent crustal earthquakes in the western (Precordillera and Western Sierras Pampeanas) terranes Lower magnitude and less frequent crustal earthquakes 600-800 km east from the trench Diario de Cuyo (Arg.), Edition of the 60th Aniversary of the 1944 EQ (01/15/2004)

  4. CHile ARgentina Geophysical Experiment (CHARGE) An NSFfunded,IRIS PASSCALproject University of Arizona,Susan Beck George Zandt, Hersh Gilbert, Patricia Alvarado, Megan Anderson, Robert Fromm, Lara Wagner, Todd Shearer INPRES, Mario Araujo, Mario Bufaliza Universidad Nacional de San Juan,Patricia Alvarado, Enrique Triep Universidad de Chile - Santiago, Jaime Campos, Javier Ruiz CHARGE field crew

  5. HURT JFR 200 km 100 km CHile ARgentina Geophysical Experiment Portable passive broadband seismic deployment 22 stations recording continuously from Nov. 2000 to May 2002 Flat slab SZ Normal SZ Slab contours from Cahill and Isacks, 1992

  6. Slab contours from Cahill & Isacks (1992); Nazca/SA vel. by Kendrick et al. (2003) PDE/NEIC seismicity during the CHARGE period (Nov. 2000 - May 2002) Modern Seismicity The Andes Cordillera and backarc region have generated > 500 crustal EQs of depths < 50 km between 29°S and 36°S in the last 20 years. Only 6.5 % of this seismicity had M > 5.0

  7. CLVD Seismic Moment Tensor Inversion (SMTI) using the CHARGE Broadband Data We used Randall et al.’s 1995 technique to model full regional CHARGE waveforms. We constrained the SMT (Foc. Mec., M0, Mw) for crustal earthquakes fixing the hypocenter and the crustal seismic velocity structure

  8. Synthetic and observed seismic displacements filtered between 15 - 50 s for the best fit (focal depth = 21 km) for event 02-117 on 27 April 2002

  9. Focal Mechanisms and Source Depths for 27 crustal (3.5 < Mw < 5.1) earthquakes recorded by the CHARGE network during 2000 - 2002 Alvarado et al., 2005

  10. (a) GPS velocity vectors in the flat slab region [Brooks et al., 2003] (b) Focal mec. solutions in vert. projection around ~31°S. [3D view and schematic cross section from Ramos et al., 2002 including seismic results around the Sierra Pie de Palo by Regnier et at., 1992 ]

  11. Event in the ESP Modelingusing the entire regional waveform to determine the moment tensor and depth of the earthquake. We find the best mechanism for this earthquake is a strike-slip focal mechanism at a depth of 5 km. We have also tested the inversion for different crustal seismic velocity models. The focal mechanism is robust and not very dependent on the velocity model assumed in the inversion.

  12. Grid search for crustal seismic velocity structures Western Sierras Pampeanas (WSP) Eastern Sierras Pampeanas (ESP) WSP (red paths) th ~ 50 km Vp ~ 6.4 km/s Vp/Vs ~ 1.80 ESP (blue paths) th ~ 30 km Vp ~ 6.0 km/s Vp/Vs ~ 1.70 mantle (Vp=8.15 km/s; Vp/Vs = 1.80)

  13. Cross-section of Stacked Receiver Functions (30°S) Moho West to east cross sections of Common Conversion Point (CCP) stacked receiver functions for the northern CHARGE transect. Positive arrivals are shown as red and negative are shown as blue. Stacked receiver functions for each column of CCP bins are shown in black. From Gilbert et al. (2006)

  14. JFR Comparison between crustal seismicity and terranes Slab contours from Anderson et al., 2006; seismicity during the last 20 years from INPRES and University of Chile; histogram from Gutscher et al., 2000

  15. CONCLUSIONS • The ESP show low Vp, low Vp/Vs and ~35-km thick crust. This correlates with a more felsic quartz-rich composition of the Pampia terrane. We find strike-slip focal mechanism solutions of shallow depths < 10 km. • The WSP (Cuyania terrane) crust exhibits high Vp and low Vs and a layered structure. These basement cored uplifts are seismically active with thrust fault focal mechanisms at depths of 14 to 26 km. This correlates with a region of a complex history of accretion, rifting and re-accretion that generated structures possibly reactivated at present times. • Changes between the crustal properties of the Cuyania terrane and the Pampia terrane and High Cordillera could be an important factor in the nucleation of crustal seismicity in the Cuyania terrane observed at historical and modern times enhanced by the flat subduction. • Broadband seismic data are very useful to study tectonic processes from an integrated point of view. Regional seismic studies are important for the asessment of the seismic hazard

  16. Stay tuned for more results after a high density deployment over the flat slab region of Argentina We plan to deploy 40 broadband PASSCAL instruments in this region to record continuously during two years (2007 - 2009)

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