Earthquake Rupture Characterization of Moderate to Micro Earthquakes
Colin Pennington
USGS
- Date & Time
- Location
- Online-only seminar via Microsoft Teams
- Summary
The detailed examination of an earthquake’s rupture is often reserved for the largest events, while smaller events are often characterized using methods that assume they have simple ruptures. This oversimplification allows us to obtain rupture characteristics for large numbers of earthquakes, but loses all information about complexity in the ruptures. Using multiple methods to characterize earthquake ruptures we explore the biases and limitations of the methods that assume a simple rupture and the benefits of examining heterogeneous ruptures of moderate (4-6M) to micro earthquakes (<3M). We examine the most common method of rupture characterization, the use of an event’s spectrum and a simple model to estimate its rupture area and stress drop. Using a wide variety of data and methods to retrieve an event’s source spectrum we find stress drop values are systematically biased depending on how site and path effects are removed, the wave type used (P-wave, S-wave), and the window length used to select the data. However, the relative stress drop values and the spatial and temporal interpretations of stress drops are consistent across methods. We then examine alternative methods of event characterization that do not assume an event’s rupture is simple to determine if smaller events exhibit rupture complexity as observed in larger events. By utilizing finite fault slip distributions and source time function analysis we find that moderate and microearthquakes often exhibit complex multiphase ruptures. The factors that influence these more heterogeneous ruptures vary with region. Prior seismicity, fault maturity, and fault structure all appear to influence the level of heterogeneity of ruptures. Combining the results from each of the above analyses, we find that that rupture complexity is not limited to large magnitude events, and the factors that control rupture complexity for large magnitude earthquakes also control them for smaller events.
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