| Abstrakt: |
Segments of many faults are observed to slip aseismically at the surface. On the central segment of the San Andreas Fault, aseismic slip accumulates largely in creep events: few mm bursts of slip which occur every few weeks to months. But even though we have observed creep events worldwide since the 1960s, we still do not know how big most events are or which forces drive them. To address this uncertainty, we systematically identify creep events along the central San Andreas Fault and determine their along‐strike rupture extents. We first use cross‐correlation and visual inspection to identify events at individual creepmeters. With data from 18 USGS creepmeters, we identify 2120 records of creep events between 1985 and 2020. We then search for slip that is closely timed across multiple creepmeters. We identify 306 instances of closely timed slip, which could indicate 306 creep events that rupture multiple creepmeter locations. Through visual inspection and statistical analysis of timing, we identify a variety of creep event types, including single‐creepmeter events, small (<2 km) events, medium‐sized (3–6 km) events, large (>10 km) events, and events that rupture multiple fault strands. The existence of many large (> $ > $few‐km) events suggests that creep events are not produced by small, rainfall‐associated perturbations; they are more likely driven by complex or heterogeneous frictional weakening and they may provide a window into the dynamics of a larger scale slip on the San Andreas Fault. Plain Language Summary: The San Andreas Fault, CA, slips at the surface between San Juan Bautista and Cholame. This slip accumulates slowly or in bursts, known as creep events. Despite observations of creep events since 1966, we still do not know how large they are or what causes them to occur. Here, we determine the length of creep events as this helps us understand more about how these events are created. If creep events are small, they may be caused by rainfall; however, if they are large, then they are likely self‐driven. Using 18 USGS creepmeters, we identify the timing of creep events and determine their length. Between 1985 and 2020 we have identified 2,120 creep events, some of which are recorded at multiple creepmeters, allowing us to determine their along strike‐length. We identify five size ranges of our creep events: isolated events, small (<2 km) events, medium‐sized (3–6 km) events, large events (>10 km), and events that occur on multiple fault strands events. These larger events are difficult to explain using conventional frictional theory and do not appear to result from rainfall. Therefore, understanding these events is important for determining the process that creates aseismic creep on faults. Key Points: Identify 2120 creep events on the central San Andreas Fault and estimate their along‐strike lengthsCreep event lengths range from sub‐km to >10 kmExistence of large events makes it likely that slip is driven by large‐scale frictional weakening [ABSTRACT FROM AUTHOR] |
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