Seismic Network at the Pierre Auger Observatory

• 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 ObservatoryProject BSR (Bloque San Rafael): PICTO Riesgo Sísmico Nº 254Agencia Nacional de Promoción de Ciencia y Técnica

Enrique G. Triep

Pierre Auger Observatory Seismic Stations Installation started on December/2009 and finished on July/2010

Data transmitted by Internet to IGSV

Stations

LOMA AMARILLA Station

LOMA AMARILLA Sensor

LOMA AMARILLA Digital Recorder and Battery

REF TEK Recorder

Protocols:TCP: communications FTP: data transferRTP (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

LOMA AMARILLA Station

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

Enlarged BSR Seismic Network

CARAPACHO Station

Autonomous station

SAN PABLO Station

Autonomous station

PAJARO BOBO Station

Autonomous station

We note that in the present project the larger part of the seismic equipment belongs to Instituto 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!

Seismic Network

Pierre Auger Observatory Stations set up from December/2009 to July/2010(Data transmitted by internet to IGSV)

Crustal earthquakes Subducted Nazca Plate earthquakes

Regional Seismicity

Las Malvinas-Nevado fault

Regional Seismicity Cross-Section

Crustal earthquakes Subducted Nazca Plate earthquakes

(km)

(km)

Crustal Seismicity

2003 earthquake and aftershocks NEIC

1929 earthquake Epicenter determined by P wave travel timesYellow cross: epicenter determined according to damaged

2002 earthquake NEIC

2003 earthquake CMT

2001 earthquake, our determinations

Cities and towns

NEIC Catalog 1977-2010

Beach balls: focal mechanism diagrams

M≈6.0 May/30/1929 EarthquakeVilla Atuel Town

Adobe Construction

M≈6.0 May/30/1929 EarthquakeVilla Atuel Town

Brick Construction

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?

After Ramos and Kay, 2006CHARGE seismic stations transect, December/2000-March/2002

Magnetotelluric experiment, 2007

Our seismic network area, December 2009-December 2013

Two previous experiments in the region

-33°-33°

Chile Argentina Geophysical Experiment (CHARGE) Broadband Seismic Network 2000/12-2002/3

Stations LENA and RAFA did not provided dataOur BSR network area

Anderson et al., 2004

Subducted Nazca plate seismicity located by CHARGE

A B A B

Earthquake magnitude: 3.2 ≤ M ≤ 3.7

Our BSR network area

Regional P and S wave travel time data were used to obtain 3D seismic tomography models for Vp, Vs and Vp/Vs

Wagner et al., 2005

Our BSR network area where tomography will be performed

We hope to solve upper mantle and crust tomography

Heit et al., 2008

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

Anderson et al., 2004

Seismic Anisotropy below the subducted Nazca plate

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.

Using SKS and SKKS waves

Our BSR network area

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

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

Next: Some examples of seismograms from our BSR network

Local Earthquake recorded at LOS LEONES StationVertical and horizontal components show clear P and S wave arrivals

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.

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

Histogram of S-P wave times from Auger Observatory data in same 40 days period before and after the Mw=8.8 Chile Earthquake

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 before

40 days after

• 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

Goals of our project

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

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 secPb 57.32 secSn 88.91 secSb 99.30 sec

The more energetic S waves are the blameworthy!

Could we see this type of effects for smaller nearby earthquakes?Earthquake origen time

Sb

70 sec

99.30 sec

After Xavier BertouPersonal comm.

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.

THANKS VERY MUCH