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Title: Directivity Modes of Earthquake Populations with Unsupervised Learning

Journal Article · · Journal of Geophysical Research. Solid Earth
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [1];  [1]
  1. California Institute of Technology (CalTech), Pasadena, CA (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
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We present a novel approach for resolving modes of rupture directivity in large populations of earthquakes. A seismic spectral decomposition technique is used to first produce relative measurements of radiated energy for earthquakes in a spatially compact cluster. The azimuthal distribution of energy for each earthquake is then assumed to result from one of several distinct modes of rupture propagation. Rather than fitting a kinematic rupture model to determine the most likely mode of rupture propagation, we instead treat the modes as latent variables and learn them with a Gaussian mixture model. The mixture model simultaneously determines the number of events that best identify with each mode. The technique is demonstrated on four datasets in California, each with compact clusters of several thousand earthquakes with comparable slip mechanisms. We show that the datasets naturally decompose into distinct rupture propagation modes that correspond to different rupture directions, and the fault plane is unambiguously identified for all cases. We find that these small earthquakes exhibit unilateral ruptures 63–73% of the time on average. Here, the results provide important observational constraints on the physics of earthquakes and faults.

Research Organization:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
USDOE Laboratory Directed Research and Development (LDRD) Program; National Science Foundation (NSF)
Grant/Contract Number:
89233218CNA000001; CCF‐1254106; AFOSR YIPFA9550‐15‐1‐0221
OSTI ID:
1604037
Report Number(s):
LA-UR-19-26206
Journal Information:
Journal of Geophysical Research. Solid Earth, Vol. 125, Issue 2; ISSN 2169-9313
Publisher:
American Geophysical UnionCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 14 works
Citation information provided by
Web of Science

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