Asthenospheric and Lithospheric Broadband Architecture from the

California Offshore Region Experiment

(ALBACORE)

Objectives
The objective of this project is to understand the tectonic interaction at the Pacific-North America plate boundary by identifying the physical properties and deformation styles of the Pacific plate and nearshore microplates. The results will be used to distinguish among contrasting upper mantle geodynamic scenarios that predict large-scale mantle flow patterns beneath western North America. Seismic studies using broadband ocean bottom seismometer (OBS) data will characterize the driving plate motion consequences of collision between the rift system, a fragmented subducted plate, the lengthening of the San Andreas transform fault system, and block rotations. The boundaries for the seismic array overlap the region of complex breakup and fracture of the Pacific plate near shore where several microplates are observed, and extend far to the west to provide comparison with oceanic lithosphere that is not fractured and has formed at a uniform rate. The results will aid in understanding the boundary forces due to relative plate motions, the driving forces and characteristics of oceanic and continental scale deformation, and how the continental margin accretionary process is influenced by offshore tectonics.

Experiment Design

• 12-month passive seismic experiment: August, 2010-August, 2011.
• 24 broadband & 10 short-period OBSs across southwestern half of Pacific-North America plate boundary.
• Collection of continuous, 40 sps, three-component waveform data.
• 13-day deployment in global-class research vessel.
• Concurrent collection of bathymetry, gravity, magnetic, sea surface temperature data

Analysis Projects

• Surface-wave dispersion and azimuthal anisotropy
• Teleseismic travel-time tomography
• SKS splitting measurements
• Local earthquake travel-time tomography and receiver functions
• Offshore seismicity patterns, relationship with faults, hypocenters and focal mechanisms
• Offshore-onshore model for tectonic evolution and lithosphere-asthenosphere seismic structure

People

Publications, posters, and abstracts

• Shintaku, N., D. S. Weeraratne, D. Scheirer, and M. Kohler, Mapping of geology and geophysical data offshore southern California, Annual SCEC Meeting Proceedings and Abstracts, Vol. XIX, Sept. 12-16, 2009. (pdf)
• Kohler, M. and D. S. Weeraratne, Marine seismic study of the Pacific-North American plate boundary, Annual SCEC Meeting Proceedings and Abstracts, Vol. XVIII, Sept. 6-11, 2008.