Department Colloquium Series

Date: 

Monday, October 17, 2016, 12:00pm

Location: 

Haller Hall (Geological Museum 102)

"Seismo-acoustic signatures of volcanic unrest and eruption" by Robin Samuel Matoza (UC Santa Barbara)

(a) Seismic vertical component velocity and (b) infrasonic pressure recordings of the 8 March 2005 phreatic (steam-driven) explosion of Mount St. Helens, Washington, USA. The broadband seismometer was collocated with the central element of a 4-element infrasound array CDWR in a quiet forest site ~13.4 km from the source. In each case, we show data from +/-1 day spanning the event at 9 March 2005 ~01:26:17 UTC (day 68). The seismic tremor accompanying the phreatic explosion has a similar amplitude to seismicity before and after. A large unambiguous infrasound signal delineates the explosive eruption.

Abstract:

Volcano seismology and volcano acoustics are two complementary methods for understanding how volcanoes work and play a vital role in volcano monitoring and hazard mitigation. Seismic data elucidate magmatic, hydrothermal, and faulting processes occurring within and around volcanoes. Infrasound is atmospheric sound with frequencies below 20 Hz, the lower frequency limit of human hearing. Infrasound is produced by shallow subsurface and subaerial processes, including explosive eruptions, shallow degassing, surface flow, and mass wasting. Explosive eruptions are seismo-acoustic phenomena, generating large-amplitude acoustic waves as well as seismic waves. Precursory and co-eruptive seismicity includes individual volcano-tectonic (VT) earthquakes, long-period (LP) (0.5–5 Hz) events, and various types of volcanic tremor. Infrasound from major sustained explosive eruptions can propagate thousands of kilometers in atmospheric waveguides and is routinely detected on sparse ground-based infrasound networks. Here I present several recent investigations that exploit seismic and infrasonic datasets at distances ranging from local to global distances from active volcanoes. We are developing and applying methods for the systematic reanalysis of waveforms from dense seismo-acoustic networks deployed on volcanoes, including high-precision earthquake relocation, acoustic localization, spectral event classification, and source mechanism inversions. On larger scales, we are developing methodologies to search systematically through multi-year data from regional and global infrasound and seismo-acoustic networks to identify, quantify, and catalog explosive volcanic eruption signals originating anywhere on Earth. [Background reading]