Monitoring of Co-Seismic Damage in the 2004 Parkfield Earthquake Using the Ambient Seismic Field

Project Description: During an earthquake, both static and dynamic strains can be large enough to break the materials surrounding the fault and near the surface. Elastic properties of these materials are thus expected to change during and after an earthquake. To monitor these properties, seismologists tend to use repeating earthquakes although these are limited in time and space. Another approach to bypass the near for earthquake is to monitor the evolution of these properties using repeated measurements of ambient noise cross-correlation functions. Under appropriate conditions, the cross-correlation of ambient noise between a pair of receivers is proportional to the Green’s function. Consequently, it enables a continuous monitoring of the velocity structure nearby a seismic array.
Brenguier et al. (2008) pointed out the spatially averaged relative velocity change, dv/v, of medium adjacent to the San Andreas fault after the 2004 Mw 6.0 Parkfield earthquake using ambient noise cross-correlation method, which can be caused by postseismic stress relaxation and coseismic off-fault damage. Wu et al. (2016) then performed the depth analysis of dv/v using a series of sensitivity kernels associated with the surface wave and the S wave velocity structure with depth, showing large dv/v in shallower crust.
In this project, we further explore this region using a larger number of seismic stations from different seismic networks to map the evolution of elastic properties in time and space with depth. We use the state-of-the-art techniques such as high-order cross-correlation (C3 method), with the 9 components of the correlation tensor between station pairs and the 6 components of the single-station correlation tensor, to enhance the temporal and spatial (horizontal and vertical) resolution of the changes in elastic properties. We employ multiple methods (stretching, MWCS, dynamic time warping, wavelet cross-spectrum) to mutually compare the results and to better evaluate the dv/v as a function of seismic frequency. We will also explore early coda measurements (sensitive to surface waves) and late coda measurements (sensitive to body waves) to better image the perturbation in 3D. The project will conclude by comparing the changes in elastic properties in light of physical models (e.g. distribution of coseismic damage, residual stress around fault) to infer earthquake damage and healing.
Intern(s): Jared Bryan
Mentor(s):

Marine Denolle, Harvard University

Site Effects in the Bay Area

Project Description: Seismic hazard analysis relies on accurately estimating ground-motion during earthquakes. Many properties affect how strongly the ground will shake during the earthquake, including properties of the earthquake itself, the crust that the seismic waves travel through, and characteristics of the site. One such characteristic is the parameter kappa, which describes how much attenuation occurs at a site - essentially how much high-frequency energy is lost at the site. Kappa is often used in models that estimate ground motion, and integrated into seismic hazard.
This project will measure kappa at various stations in the San Francisco Bay Area. This includes processing seismic waveforms at various stations, computing the frequency content of these waveforms, running an inversion with pre-existing code to find the part of the waveform that exists because of site effects, and then using this to compute kappa. This information will be important in future seismic hazard calculations in the region.
Intern(s): Elias King
Mentor(s):

Valerie Sahakian, University of Oregon / US Geological Survey

Multidisciplinary Investigation of Determining Channel Incision Ages in the Carrizo Plain, California

Project Description: Intern will be involved in routine processing of Sentinel-1 data. Most of the processing steps are now fully automated, and can be executed with little human supervision. Interns can quickly learned how to download and process the data, and in fact are instrumental in developing scripts for further automating the processing chain. A previous intern recently got an outstanding student award from San Diego Association of Geologists (SDAG) for his work on a SCEC-sponsored project. We would be happy to involve an extra intern under the auspices of this project.
Intern(s): Salena Padilla
Mentor(s):

Sinan Akciz, California State University, Fullerton

Dating Ductile Shear Zones in Southern California

Project Description: This project involves titanite geochronology to document the timing of ductile deformation in the Borrego Springs and Santa Rosa Mylonite zones. The mylonite zones are important because they are a natural analog for the deep crustal rocks in the vicinity of the brittle-plastic transition (BPT) beneath the San Andreas Fault system, and modeling the rheology of these BPT rocks is a critical element of the SCEC Community Rheology Model. We will use U-Pb isotopes to date titanite to document the timing of deformation and Zr-in-titanite thermometry on titanite neocrysts within the deformational fabric to measure the temperature of fabric development. Students will gain experience with field work, mineral separations, scanning electron microscopy, and laser-ablation mass spectrometry.
Intern(s): Jennifer Bautista
Mentor(s):

Elena Miranda, California State University, Northridge

Dating Crust Formation in the Eastern Peninsular Ranges Batholith

Project Description: This project involves zircon geochronology to date the timing of crust forming events in the Eastern Peninsular Ranges Batholith. This information will provide ages for host rocks that were deformed by ductile shearing in the Santa Rosa and Borrego Springs mylonite zones. These shear zones are the target of study because they represent the deep crustal analogue for the BPT rocks under the San Andreas Fault System that will be characterized as part of SCEC's Community Rheology Model. The host rocks will provide a maximum age for the timing of deformation, and we will use cross-cutting dikes to determine when deformation ceased. We will use U-Pb isotopes to date zircons from deformed and undeformed rocks. The intern will gain experience with field work, mineral separations and laser-ablation mass spectrometry.
Intern(s): Adam Brackman
Mentor(s):

Joshua Schwartz, California State University, Northridge