Roland Bürgmann
David R. Shelly
Christopher Johnson
Taka'aki Taira
Lian Xu
2018
<p><span>Earthquake swarms represent a sudden increase in seismicity that may indicate a heterogeneous fault-zone, the involvement of crustal fluids and/or slow fault slip. Swarms sometimes precede major earthquake ruptures. An earthquake swarm occurred in October 2015 near San Ramon, California in an extensional right step-over region between the northern Calaveras Fault and the Concord–Mt. Diablo fault zone, which has hosted ten major swarms since 1970. The 2015 San Ramon swarm is examined here from 11 October through 18 November using template matching analysis. The relocated seismicity catalog contains ∼4000 events with magnitudes between </span><span class="math"><span id="MathJax-Element-1-Frame" class="MathJax_SVG" data-mathml="<math xmlns="http://www.w3.org/1998/Math/MathML"><mo is="true">&#x2212;</mo><mn is="true">0.2</mn><mo is="true">&lt;</mo><msub is="true"><mrow is="true"><mi is="true">M</mi></mrow><mrow is="true"><mi mathvariant="normal" is="true">d</mi></mrow></msub><mo is="true">&lt;</mo><mn is="true">3.6</mn></math>"><span class="MJX_Assistive_MathML">−0.2<<i>M</i><sub>d</sub><3.6</span></span></span><span>. The swarm illuminated three sub-parallel, southwest striking and northwest dipping fault segments of km-scale dimension and thickness of up to 200 m. The segments contain coexisting populations of different focal-mechanisms, suggesting a complex fault zone structure with several sets of en échelon fault orientations. The migration of events along the three planar structures indicates a complex fluid and faulting interaction processes. We searched for correlations between seismic activity and tidal stresses and found some suggestive features, but nothing that we can be confident is statistically significant.</span></p>
application/pdf
10.1016/j.epsl.2018.02.018
en
Elsevier
Kinematics of the 2015 San Ramon, California earthquake swarm: Implications for fault zone structure and driving mechanisms
article