SCEC Award Number 15132 View PDF
Proposal Category Travel Only Proposal (SCEC Annual Meeting)
Proposal Title The Mechanics of Tremors in the Deep San Andreas Fault
Investigator(s)
Name Organization
Sylvain Barbot Nanyang Technological University (Singapore)
Other Participants
SCEC Priorities 5d SCEC Groups FARM, Seismology, Simulators
Report Due Date 10/16/2015 Date Report Submitted 10/17/2015
Project Abstract
 A particular tremor family deep below the San Andreas Fault (SAF) exhibited doubling recurrence intervals alternating between about three and six days. Our physics-based model with single homogenous asperity can explain the double recurrence intervals of the tremor source. The observed source characteristics show that tremor bursts conting more low-frequency earthquakes (LFEs) are associated long duration. Here, we investigate the physics of the micro-asperities under rapid loading to model the number of LFEs in a burst and the tremor duration. We find that the observed number of LFEs per burst is controlled by peak velocity of the modeled slip event. However, the duration of the observed tremor burse is not directly controlled by the duration of the modeled slip event. The results reveal that the LFEs are triggered shortly after the slip events, adn the mechanism is similar to mainshock/aftershock interactions. Our numerical study may enable us to decipher the fundamental difference between tremors and earthquales in terms of their moment and duration.
Intellectual Merit We developed a physics-based model to understand the trmore recurrence intervals, which may provide insight into the understanding the effect of pore pressure change on recurrence interval variability of the earthquakes. Our model explains the period-doubling phenomenon fo the tremor family, which is not previously explained. We are creative in applying the occurrence of low-slip and fast-slip events to explain the doubling intervals of the tremor family.
Broader Impacts A significant contribution was made by a female graduate student (underrepresented).
Exemplary Figure Figure 1. Recurrence pattern of the period-doubling Parkfield tremors and numerical simulations. A) Observed tremor recurrence pattern and number of LFEs per burst, modified from Shelly (2010). Each tremor burst consists of 1 to 5 LFEs in most cases. Burst preceded by a shorter recurrence interval are associated with more LFEs throughout the sequence (consecutive burses are connected with a gray line). The regular oscillation of recurrence intervals between about three to six days is from mid-2003 to the onset of the 2004 Parkfield earthquake. The sudden disappearance of the 6-day recurrence intervals coincides with the 2004 Parkfield earthquake. The gradual recovery of recurrence intervals is from the onset of the Parkfield earthquake to the end of 2007, around two years. B) Numerical simulation of the Parkfield tremor activity incorporating a change in effective confining pressure (red profile) after the Parkfield earthquake. The colored circles denote the maximum velocity of the slip events. Fast ruptures are preceded by shorter recurrence intervals. The 2004 Parkfield earthquae results in a rapid occurence of slip events, followed by a sequence of multiplets with varying period-multiplying factors.
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