Seismic Network at the Pierre Auger Observatory

1. Seismic Network at the Pierre Auger Observatory Enrique G. Triep • Instituto Geofísico-Sismológico Ing. F. S. Volponi (IGSV), Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de San Juan • Instituto Nacional de Prevención Sísmica (INPRES) • Departamento de Sismología, Facultad de Astronomía y Geofísica, Universidad Nacional de la Plata (Dep. Sism., UNLP) • Pierre Auger Observatory Project BSR (Bloque San Rafael): PICTO Riesgo Sísmico Nº 254 Agencia Nacional de Promoción de Ciencia y Técnica

2. Pierre Auger Observatory Seismic Stations Installation started on December/2009 and finished on July/2010 Data transmitted by Internet to IGSV Stations

3. LOMA AMARILLA Station

4. LOMA AMARILLA Sensor

5. LOMA AMARILLA Digital Recorder and Battery REF TEK Recorder Protocols: TCP: communications FTP: data transfer RTP (Real Time Protocol): monitoring Other recorders installed in the network (SARA and PCN digitizers) with Linux system: access by SSH and data retrieval by SFTP

6. LOMA AMARILLA Station

7. Enlarged BSR Seismic Network Pierre Auger Observatory Stations since December/2009- July/2010 (Data transmitted by internet to IGSV) Autonomous Stations since December/2010 Autonomous Stations to be installed within 2011

8. CARAPACHO Station Autonomousstation

9. SAN PABLO Station Autonomousstation

10. PAJARO BOBO Station Autonomousstation

11. We note that in the present project the larger part of the seismic equipment belongs toInstituto Geofísico-Sismológico Ing. F. S. Volponi (IGSV), UNSJ, and a smaller part to the Instituto Nacional de Prevención Sísmica (INPRES). There are no borrowed equipment!

12. Seismic Network Regional Seismicity Pierre Auger Observatory Stations set up from December/2009 to July/2010 (Data transmitted by internet to IGSV) Crustal earthquakes Subducted Nazca Plate earthquakes Las Malvinas-Nevado fault

13. Regional SeismicityCross-Section (km) (km) Crustal earthquakes Subducted Nazca Plate earthquakes

14. Crustal Seismicity NEIC Catalog 1977-2010 2001 earthquake, our determinations 2002 earthquake NEIC 2003 earthquake and aftershocks NEIC 2003 earthquake CMT 1929 earthquake Epicenter determined by P wave travel times Yellow cross: epicenter determined according to damaged Cities and towns Beach balls: focal mechanism diagrams

15. M≈6.0 May/30/1929 Earthquake Villa Atuel Town Adobe Construction

16. M≈6.0 May/30/1929 Earthquake Villa Atuel Town Brick Construction

17. Thus, the area is seismically active and has important destructive earthquakes. What we know from geophysical work up to now and what would like to know from our experiment?

18. Two previous experiments in the region After Ramos and Kay, 2006 CHARGE seismic stations transect, December/2000-March/2002 Magnetotelluric experiment, 2007 Our seismic network area, December 2009-December 2013

19. Chile Argentina Geophysical Experiment (CHARGE) Broadband Seismic Network 2000/12-2002/3 -33° Stations LENA and RAFA did not provided data Our BSR network area

20. Subducted Nazca plate seismicity located by CHARGE Earthquake magnitude: 3.2 ≤M ≤ 3.7 Our BSR network area A B A B Anderson et al., 2004

21. Regional P and S wave travel time data were used to obtain 3D seismic tomography models for Vp, Vs and Vp/Vs Our BSR network area where tomography will be performed We hope to solve upper mantle and crust tomography Wagner et al., 2005

22. Stacked S Receiver Functions We aim to determine 3D Moho morphology (not only in one cross-section as in this case) using converted P to S waves, receiver functions, etc. Heit et al., 2008 Heit et al., 2008

23. Seismic Anisotropy below the subducted Nazca plate Using SKS and SKKS waves Interpretation (considering fast seismic directions same as the mantle flow): South of 33º S, mantle flow is parallel to the trench. North of 33º S, mantle flow tend to be perpendicular to trench. That is, the flow escape to the East under the flat slab. Our BSR network area Anderson et al., 2004

24. We will work with SKS and SKKS waves to determine upper mantle seismic anisotropy below the Nazca plate, and with S waves from local earthquakes for the upper mantle above the plate

25. Magnetotelluric (MT) 2D preliminary data analysis at 34º S, below the Payún Matru Volcanic Field, suggest a “tentative identification” of a conductive mantle plume from 200 km depth to at least 40 km below the surface (Burd et al., 2008) Warning: Do not thrust the details of this structure at this time! Only consider that a narrow, near vertical conductive structure must connect the shallow to deep mantle We will look for features like this in our experiment region using tomography and seismic anisotropy

26. Next: Some examples of seismograms from our BSR network

27. Local Earthquake recorded at LOS LEONES Station Vertical and horizontal components show clear P and S wave arrivals

28. Mw=8.8 Chile Earthquake, February/27/2010 as was recorded in LOS LEONES station. The digital recorder did not have enough “Gain” and the signal was saturated. The gradual signal onset is a common characteristic of the Chile earthquakes when they are recorded in western Argentina.

29. Mw=8.8 Chile Earthquake, February/27/2010, as was recorded in LOS LEONES station after filtered between 1 and 5 Hz

30. Histogram of S-P wave times from Auger Observatory data in same 40 days period before and after the Mw=8.8 Chile Earthquake 40 days before S-P times ~ 10-14sec are from local earthquakes Note the large increase of local earthquakes after the great earthquake The great earthquake activated seismic activity in the Argentine side! 40 days after

31. Goals of our project • Precise Location of the Crust and Nazca Plate seismicity • Focal Mechanisms (First P wave motion and Moment Tensor Inversion) • Seismic Tomography • Seismic Anisotropy • Results correlated with tectonic and geodynamical features

32. Some small interdisciplinary collaboration already done: Explanation of which was the wave from Chile Mw=8.8, February 27, 2010, earthquake that caused the effect on the water tanks transparence at the Pierre Auger Observatory

33. Auger Observatory Average Background Events Rate versus Time (operation as Geiger mode) Water transparency decrease during about 70 sec: 24 σ (sigmas!) Mw=8.8, 2010, Chile Earthquake Epicentral distance to Los Morados Fluorescence station: 3.27º Waves travel time: Pn 49.91 sec Pb 57.32 sec Sn 88.91 sec Sb 99.30 sec The more energetic S waves are the blameworthy! Could we see this type of effects for smaller nearby earthquakes? Sb 99.30 sec 70 sec Earthquake origen time After Xavier Bertou Personal comm.

34. CONCLUSIONS • The opportunity to install seismic stations at the Pierre Auger Observatory, taken advantage of its building facilities, internet, power, and specially the help of its people, have been of an immense platform from which we were able to start and develop our research project. • We propose to establish a digital broadband permanent seismic network at the Pierre Auger Observatory. • The network operation and supervision should be under the three only institutions in Argentina that works in seismology: Instituto Geofísico-Sismológico Ing. F. S. Volponi (IGSV), UNSJ, Instituto Nacional de Prevención Sísmica (INPRES), Departamento de Sismología, UNLP. INPRES is taking care of the National Seismic Network in Argentina, and has an up to date laboratory and technical expertise to control, calibrate and repair sensors and data loggers. • The network should have open data accessibility, and at least one of the stations should make the data availability in real time. • Clearly, other geophysical fields would benefit with the infrastructure, organization, and support of the Pierre Auger Observatory.

35. THANKS VERY MUCH