Forty Years of Controlled Source Crustal Imaging
Tom Brocher
USGS
- Date & Time
- Location
- Hybrid In-Person and Online seminar via Microsoft Teams
- Host
- Walter Mooney
- Summary
My talk reviews a few of the many contributions of the Earthquake Science Center’s active source crustal imaging group since 1985. While a postdoc at the University of Hawaii in 1982, I collaborated on with Tony Watts and Uri ten Brink at LDEO on a project that developed evidence that the Hawaii hotspot magmatically underplated the oceanic crust as well as formed volcanic edifices on top of it. After joining the USGS in 1985, we responded to the 1989 Loma Prieta earthquake by conducting a number of studies of crustal structure of the Bay Area. These studies provided evidence for a slab of remnent oceanic crust beneath the continental margin and helped image a large seismic velocity contrast across the Hayward Fault. Between 1998 and 2002 we conducted four different crustal imaging studies in the Puget Lowland, facilitating the discovery of a Holocene fault scarp along the Tacoma fault and helping to define the geometry of the Seattle basin. In addition, we were able to demonstrate the widespread occurrence of hydrated (serpentinized) upper mantle in the Cascadia forearc. Finally, to commemorate the 150th anniversary of the 1868 Hayward earthquake we compiled public records for expenditures totaling $75-80B in the Bay Area for building retrofits and replacement since 1989. These expenditures help quantify the societal benefits of the work conducted by the USGS Earthquake Hazard Program over the years.