New Techniques Using High-Density Seismic Array Data Analysis to Determine 3-D Fault and Crustal Structures in the Long Beach Basin
Abstract
Determining the depth orientation of the Newport-Inglewood Fault and other crustal
structures beneath large cities can improve the hazard analysis of large magnitude earthquakes.
Details of fault depth structure can also evaluate potential fault and crustal layer interactions
beneath populated areas or regions of interest. We propose a new method to find crustal layer
discontinuities utilizing point cloud methods derived from passive seismic data recorded in Long
Beach, California, from 2011-2012. Using a high-density array of 7,781 geophones within a
98-square-km area allows for excellent resolution of detailed structures at crustal depths. The
methodology provided here may prove to be a cost-effective way for seismologists and
companies to check hypotheses using passive seismic data before fully deploying or processing
data from an active source experiment. We first create a 3D model of the autocorrelated passive
data. Clear planes or surfaces within the 3D seismic data set are then located, and points
determined to not be in the layer are removed. We isolate each structural plane separately and
connect each point in the point cloud to another point forming small triangles. Each of the
triangular surfaces are filled in using Delaunay triangulation. We find that the Moho is dipping
inland at a 25° angle from horizontal with a slight curve in the upper 6 km. Crustal boundaries,
such as the upper crust, lower crust, and several minor layers in between, are also identified. The
three-dimensional structure of the northwest-southeast trending Newport-Inglewood Fault and
Los Alamitos Fault are also identified. This three-dimensional analysis of crustal structure will
aid in hazard analysis in the immediate Long Beach area and can potentially be replicated in
other seismically active areas where there is little knowledge of the underlying crustal structure.
AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019