Developing Methods for Detection and Analysis of Repeating Earthquakes and Low Frequency Earthquakes Using Cascadia Initiative Amphibious Network Data

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The Pacific Northwest is subject to earthquake and tsunami hazard associated with the Cascadia subduction zone, due to recurring slip on the plate boundary fault that separates the North America plate and the downgoing Pacific plate. Slip varies in time and space along the fault and understanding the slip patterns can lead to new insights about which fault sections are most likely to produce damaging 'megathrust' events (greater than magnitude 8). By studying smaller events that occur throughout a seismic cycle (loading, rupture, post seismic, reloading etc) this study can provide context for updated regional hazard assessment. An undergraduate intern and a PhD student will receive seismology training using both onshore and offshore data. A portion of the spectrum of slip behaviors along the Cascadia megathrust fault will be studied using seismic data from the Amphibious Array- reoccupied EarthScope Transportable Array sites and OBSIP ocean bottom seismometers. Small repeating earthquakes will be documented for the 4-yr duration of Cascadia Initiative (CI) and their distribution will be interpreted in terms of fault character and possible along-strike variation in structure within the subducting plate. The offshore coverage is expected to eliminate a current bias in observations where onshore-only results suggest that low frequency events (LFE) only occur in the down-dip part of the seismogenic zone. A pilot study confirms that the planned automated spectral detection method can succeed on CI ocean bottom seismometer data. There is potential for shallow repeating events to occur in the up-dip portion of the megathrust zone and there may be variations in level and type of source signature, including possibly new LFE, along the Cascadia subduction zone. A lesson designed for an undergraduate course will be developed and archived on the IRIS InClass and SERC servers. The event catalog and source parameter results will be made available via publication supplements and at least one NSF-supported open database (IEDA).