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Preliminary Imaging Results From a Nodal Array to Investigate the Structure of the Southern Cascadia Forearc

Description: 

Numerous variations in the tectonic and seismogenic behavior of the Cascadia forearc appear linked through subduction-mediated processes, such as non-volcanic tremor density, episodic tremor and slip (ETS) recurrence interval, uplift and exhumation rates, intraslab seismicity, slab dip, plate locking, and topography. These correlations are particularly pronounced in Southern Cascadia, where the shortest slow slip recurrence intervals, the highest amount of non-volcanic tremor, and the broadest forearc topography are found. Despite this, the southern Cascadia forearc has been relatively under-instrumented with modern passive seismic equipment. As such, better seismic images are needed before robust comparisons with other portions of the forearc can be made.

From March - April 2020, the Southern Cascadia Earthquake aNd Tectonics ARray (SCENTAR) was deployed to investigate the forearc structure in northernmost California. This array consisted of 60 continuously operating 3-component nodal seismometers (an ~8-fold increase compared to long-term seismic monitoring in the area) with an average station spacing of ~15 km. Analysis of the noise spectrum on these instruments are comparable to nearby broadband instrumentation down to ~0.1 Hz, which overlaps with frequencies commonly used for passive seismic imaging. Teleseismic vertical P-waveforms are nearly identical on nodal and broadband instruments, allowing for the computation of receiver functions to image the local discontinuity structure. Despite only 1-month of data, the preliminary receiver function images show a very similar structure to what has been collected in the prior decade of permanent and temporary seismic stations. In addition, ambient noise interstation cross-correlations show reliable surface wave arrivals up to 15 second periods, which will allow for higher lateral sampling and shallower sensitivities than previous datasets could obtain. This dataset highlights the feasibility of using short-term nodal arrays and passive imaging techniques to recover the seismic structure in hard-to-reach regions at a relatively low cost.

Session: Crustal Imaging of High Seismic Hazard Regions [Poster]

Type: Poster

Date: 4/20/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Jonathan Delph

Student Presenter: No

Invited Presentation: 

Authors