PeruSE - Peru Subduction Experiment

PeruSE is a cooperative involving the Tectonics Observatory at Caltech, the Center for Embedded Network Sensors (CENS) at UCLA, and the Institute for Geophysics, Peru (IPG). It is funded by the Betty and Gordan Moore Foundation, the NSF-CENS project, and NSF award "Collaborative Research: The Peru Subduction Zone Experiment (PeruSE) a Seismic Investigation of the Role of Water in the Lithospheric Dynamics of Sunduction Zones" (EAR-1045683).

The PeruSE arrays are deployed along 4 lines, each of which (except for Line 4) have nominally 50 sensors when fully occupied, and 25 when only every other station is in place. Details of the data recorded for each line are availble here . The deployment dates and rationale for each line are:

  • Line 1 started 2008/07 with 50 sensors, and was reduced to half density in 2010/08. The purpose of this line is to sample the subduction system where the slab dip is normal (30 degrees).
  • Line 2 started 2009/12 and continued to 2011/06 when it was changed to 50% density. The line covers the transition between the normal dipping region to the south and the shallow-flat dipping portion to the north. Along the line, the slab depth changes from 250 to 100 km (south to north).
  • Line 3 started at half density on 2010/11 and was fully densitified on 2011/08. This line is intended to sample the flat portion of the slab.
  • Line 4 has only 4 stations that were deployed on 2011/08. It is intended to complete the box so that ambient noise correlations will have better converage, and to aid in the analysis to distance surface waves.

Participants:

Tectonic Observatory, Caltech
  • Robert Clayton
  • Richard Guy
  • Kristin Phillips-Alonge
  • Steve Skinner
  • Yiran Ma
CENS, UCLA
  • Paul Davis
  • Igor Stubailo
Peru
  • Jhonny Tavera, IPG
  • Victor Agular
  • Lawrence Audin, IRD

Publications

  • Phillips, K., R. Clayton, P. Davis, H. R. Guy, S. Skinner, I. Stubailo, L. Audin, and V. Aguilar, Structure of the Subduction System in Southern Peru From Seismic Array Data, J. Geophys. Res, 117, B11306, doi:10.1029/2012JB009540.
  • Skinner, S. and R. Clayton, The lack of correlation between flat slabs and bathymetric impactors in South America, submitted to EPSL, July, 2012.
  • Ma, Y., R. Clayton, Z. Zhongwen, and V. Tsai, Locating a Scatterer in the Active Volcanic Area of Southern Peru from Ambient Noise Cross-correlation, submitted GJI, July, 2012.
  • Phillips-Alonge, K. and R. Clayton, Structure of the Transition Region Region from Seismic Array Data in Southern Peru, submitted to GJI, Oct 2012.
Pictures of Station Deployment. The data logger, charge controller and battery are contained in the metal box, which variably put above ground, on the mast, and below ground. The sensor is housed in the buried plastic container, which has a concrete base and is foam-filled to provide thermal installation. The mast supports the solar panel and the GPS clock antenna. The mast in the right panel is also supporting the radio antenna that is part of the CENS network.
Data Sample From Line 1. The plot shows the initial 400 sec of a Mw=7.3 event located in the Philippines, approximately XXX degress from the Peru array. The data have been bandpass filtered 10-100 sec, to suppress local seismicity. The lateral continuity of the various phases shows that the sensors are performing quite well.
Receiver Function Results Beneath Line 1. Both panels show the same image, which is formed by a stack over events of receiver functions that that are back-projected along the P-wave raypath. In the right panel, the major features are denoted with thin yellow lines and labelled on the right. MC is a positive impedance mid-crustal layer that is interpretated as the interface with the underthrust Brazillian Shield. The Multiple is a PmPs crustal multiple. The triangles are Moho depth estimated from the Ps converted phases and its multiples via the method of Zhu and Kanamori (2000).
Comparison of Receiver Function Results For P, PP, and PKP Phases. The Peru array is situation such that most of the major earthquake zones are beyond the 30-90 degree window for allowable P-waves (to avoid complications of overlapping phases). To include the most distant events, we use other phases such as PP and PKP. The three panels show the receiver function images for P, PP and PKP respectively. Note that the PKP phases arrive at too steep an angle to produce a measureable converted phase (PKPs) for horizontal layers (i.e. the Moho and mid-crust), but are capable of imaging the slab because of its 30-degree dip.
Tomography for Line 1. The left column shows the P-wave tomography results. In the upper panel the variations are in terms of slowness variations, and shows a maximmum variation over the whole plot of about 14%. The lower plot shows the same results as a function of absolute velocity. The Moho and slab interfaces determined from receiver functions are shown along with the local seismicity. The right column shows the checkerboard resolution test, with top being the input chekerboard, and trhe bottom being its tomoraphic reconstruction. The test indicates good resolution across the entire line to a depth 300 km. Note that both local and telesiesmic events are used. The panels in this figure are from P. Davis, UCLA.
Line 2 Receiver Function Images The upper left shows the stacked reeciver functions for Line 2. The left of the plot is the end near Lake Titicaca where it crosses Line 1, and the right end crosses Line 3. The mid-crustal layer and Moho are clear. A poor image of the slab rises from 225 km on the left to 100 km where it intersects Line 3. The lower left shows a single event receiver function. The upper right is a model for finite-difference modeling derived from the RF images. The lower left shows the simulated RFs.
Line 2 Migrated Images The RF finctions along Line 2 where migrated resulting in the image shown here. The slab interface is better resolved than with the unmigrated image.
Line 3 Receiver Function Images The RFs for Line 3 are shown. The Moho and mid-crust layers are evident as well as the flatten slab, at least to the 200 km distance.
Comparison of Line1 (Normal Dip Subduction) and Line 3 (Flat Subduction) The images and models are normal dipping slab (above) and the flat slab (below) are shown.
Synthetic Models The models and the finite-difference models synthetic receiver functions are shown for all 3 lines.
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