New techniques in point cloud analysis of high-density seismic array data to determine three dimensional fault and crustal structures in the Long Beach Basin

Andrew Allevato, Robert W. Clayton, & Dayanthie S. Weeraratne

Published August 15, 2018, SCEC Contribution #8669, 2018 SCEC Annual Meeting Poster #096

The lack of knowledge of crustal structure and fault surface behavior at depth can adversley affect earthquake hazard analysis in highly populated areas. Interactions between faults and crustal layers at depth may also be important. Using passive seismic data recorded in Long Beach, California from 2011 to 2012, we propose a new method to find crustal layer discontinuities utilizing point cloud methods. This is a high-density study using 7,781 geophones within a 98 square km area, which allows for excellent resolution of detailed structures at crustal depths. The development of this new methodology may prove to be cost-effective, while also providing a way for seismologists and companies to check hypotheses using passive seismic data before fully deploying an active source experiment. We first create a 3D model of the autocorrelated passive data. We then locate clear planes or surfaces within the 3D seismic data set. We isolate each structural plane separately and connect each point in the point cloud to another point forming small triangles. Each of the trianglar surfaces are filled in using Delaunay triangulation. The three dimensional structure of the northwest-southeast trending Newport-Inglewood Fault is identified from point cloud analysis. We observe that the Moho is dipping inland at a 25-degree angle from horizontal. Major crustal boundaries, such as the upper crust, lower crust, and several minor layers in between, are also identified. These results can be used in hazard analysis of the Long Beach area, while also giving us a better understanding of the Long Beach Basin in general.

Key Words
passive seismic, Long Beach, 3D

Citation
Allevato, A., Clayton, R. W., & Weeraratne, D. S. (2018, 08). New techniques in point cloud analysis of high-density seismic array data to determine three dimensional fault and crustal structures in the Long Beach Basin. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology