Marine Seismology

 

A primary research focus of my group in recent decades has been marine seismology. The scale of these studies has varied by two orders of magnitude from detailed studies of ocean ridge crest structure and hydrothermal systems to regional studies of upper mantle structure. In the mid 1990’s my group developed one of the first fleets of broad band OBSs capable of long duration deployments enabling the first regional scale OBS experiments studying the oceanic upper mantle (MELT, TOES, GLIMPSE) and above subducting slabs ( LABATTS).  The recently completed ELSC seismic experiment focussed on the structure of back arc basins and subduction zones. The HOBITTs experiment combines OBSs with high resolution APGs (another development of my group) to study SSEs on a subduction zone.


The LDEO OBSs group is now part of OBS Instrument Pool (OBSIP) and is managed by Andrew Barclay and supported by NSF with instruments available to any P.I. writing a successful NSF grant. The LDEO OBS group constructed 30 OBSs in support of the Cascadia Initiative, a four year deployment of OBSs across the Cascadia margin and Juan deFuca plate.  Fifteen of these instruments were trawl shielded (TRM) OBSs (left). The instruments were designed for shallow water and feature a massive steel shield to protect the instrument from loss due trawling and also to protect the sensor from ocean floor current, significantly reducing the noise level. Horizontal component noise levels on OBS are typically very high due to tilt noise from current, but some TRMS despite high current levels in shallow (<100m) water have recorded very low noise levels.  Ocean waves produce very high noise levels on the vertical components due to wave loading (eg. Webb and Crawford, 2010), the deployment of high resolution, high rate APGs allows removal of most of this noise even at the shallowest sites. The huge dynamic range of the APGs allow these sensors to be used as strong motion sensors for large earthquakes.

The trawl and current shield (TRM) OBS. The heavy shield protects the recording electronics, seismic sensor, and APG which lie within. A pop-up float is used to recover the TRM in water depths to 250m.