SCEC Award Number 17100 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Static and dynamic source parameters of global strike-slip earthquakes
Investigator(s)
Name Organization
Marine Denolle Harvard University
Other Participants Chris Van Houtte (postdoc)
SCEC Priorities 3c, 4a, 4b SCEC Groups Seismology, GM, FARM
Report Due Date 06/15/2018 Date Report Submitted 06/15/2018
Project Abstract
 Strike-slip earthquakes are significant contributors to the seismic hazard in Southern California due to the dominant transform plate boundary. Understanding the source characteristic of these strike-slip earthquakes is critical to improving estimates of the seismic hazard and in particular for ground motion prediction. Two key parameters are thought to dominate strong ground motions: pulse duration for a given earthquake moment, often parameterized with a static stress drop parameter , and earthquake radiated energy ER, which captures the level of high-frequency radiation at the source. Several studies found systematic spectral shapes that exhibit two corner frequencies (Denolle and Shearer 2016, Archuleta and Ji 2016). The lower corner frequency corresponds to the inverse of the source duration, while the higher corner frequency’s origins remain unclear. Between both corner frequencies, Denolle and Shearer (2016) show that the intermediate falloff rate is , a weaker falloff that increases the amount of high frequencies in the ground motion. For Southern California, the two-corner spectrum model, is likely to be representative of a large magnitude earthquake from the San Andreas Fault, because elongated strike-slip earthquakes exhibit pulse-like behavior (e.g. 2002 Denali, 2001 Kokoxili, 2012 Sumatra). It is therefore necessary to understand the relationships between the second corner frequency, and ER for large strike-slip earthquakes. Given that the second corner frequency is only observable for large magnitude earthquakes, this analysis cannot be undertaken using Southern California data alone. Instead, we propose to examine a global dataset of strike-slip earthquakes.
Intellectual Merit Our preliminary results may constrain the rise time of strike-slip earthquakes, which remain invariant with earthquake magnitude. Our preliminary work suggests that most strike slip earthquakes are pulses, and that this behavior becomes dominant with earthquake size.
Broader Impacts The impact of characterizing strike-slip source pulses will help better constrain ground motion predictions, whereby source models have to be imposed. It has direct implication to seismic hazard assessment. The project involves a master student from Paris and lead PI Denolle to introduce numerical tools and seismology to an Earth science student.
Exemplary Figure Figure 2: Corner frequency estimates for 172 strike slip events: blue and red circles: first corner frequency of global thrust events (Denolle and Shearer 2016) and of this study, respectively. Purple and green circles, second corner frequency of global thrust events (Denolle and Shearer 2016) and of this study, respectively. Black line shows the best-fit linear trend for magnitudes 6 and greater, were the differences between single-fc model and double-fc model becomes significant.

Note that this figure will be updated by the end of the internship and please request an update if the figure will be placed in the science highlights.