[ghsc-seminars] January 25th @ 10am, USGS-GHSC Seminar: Dave Shelly

[Mirus, Benjamin]

*"**New Frontiers in Characterization of Sub-Catalog Microseismicity:
Application to Fluid-Driven Earthquake Swarms Beneath Long Valley Caldera,
California**"*

*Dr. Dave Shelly, USGS Earthquake Science Center, Menlo Park, CA*

Microseismicity often conveys the most direct information about active
processes in the earth’s subsurface. However, routine network processing
typically leaves most earthquakes uncharacterized. These “sub-catalog”
events can provide critical clues to ongoing processes in the source
region. To address this issue, we have developed waveform-based processing
that leverages the existing catalog of earthquakes to detect and
characterize events absent in routine catalogs.  Using large-scale waveform
cross-correlation between cataloged events with the continuous data stream,
we 1) identify events with similar waveform signatures in the continuous
data across multiple stations, 2) precisely measure relative time lags
across these stations for both P- and S-waves, and 3) estimate the relative
polarity between events by the sign of the peak absolute value correlations
and its height above the secondary peak.  This final step facilitates
robust focal mechanism estimation for large populations of tiny
earthquakes, addressing a common shortcoming in microseismicity analyses
(Shelly et al., JGR, 2016).  Depending on the application, we can
characterize 2-10 times as many events as included in the initial catalog.
Application to a 2014 swarm in Long Valley Caldera, California, illuminates
complex patterns of faulting that would have otherwise remained obscured.
Together, these patterns imply strong interactions between fluid diffusion
and faulting processes in the crust.

*Thursday, January 25th, 2018*
*10-11 am​  (Mountain Time)*
*USGS, 1711 Illinois Street, Golden, CO*
*Entry Level Seminar Room*

*Note: Please arrive *~5 minutes early* and *bring photo ID* for
airport-style security measures now in place at the USGS building.

Thank you,
GHSC Seminar Committee

Mirus, Ben - bbmirus at usgs.gov
Josh Rigler - erigler at usgs.gov
Oliver Boyd - oboyd at usgs.gov

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