Michael West

Lamont-Doherty Earth Observatory
of Columbia University

Environmental Geophysics interests
Arguably the most important part of the solid Earth is the top 10-100 meters. This is the region with the greatest impact on agriculture, construction and waste burial. Yet it is one of the most difficult to understand. We know more about Earth's core than many shallow environmental systems.

I work to develop methods of imaging features in the near-surface. My particular interest is in tracking fluid distribution using non-invasive seismic/geophysical techniques. Well-monitoring and chemical tracer studies are often used with the same objective. But geophysical approaches can offer continuous monitoring without gaps between data points. Such "4-D" methods have revolutionized oil production. With advances in instrumentation and processing, similar approaches are quickly becoming cost-effective tools for subsurface environmental assessment. Applications include monitoring aquifer depletion and recharge, tracking chemical spills and evaluating groundwater remediation efforts.

Tracking near-surface fluid distribution
This project used a novel method to monitor the depth of a water table. It was conducted on a sandy beach in East Hampton, NY. A 12-hour tidal cycle forced the water table under the beach to rise and fall. This variation through time was captured using a multi-channel seismic array. Surface waves were used to invert for the shear velocity structure, which is very sensitive to the presence of fluids. This project also demonstrated the feasibility of using such methods to address water resource issues.
Test of 22 calibre and shot pipe seismic sources
All seismology projects require a source. Earthquakes illuminate Earth's deep interior while explosives provide good sources for regional studies. In the near-surface environment, very small sources are required. This comparison study evaluated the source characteristics of a sledge hammer, a shot-pipe (powered by 12-guage shot gun shells) and a smaller similar device which used 22 calibre shells. Each sources has a distinct signature. The results will improve future studies by allowing us to select the best source for a given project.
Tack hammer source test
This study was similar to the 22 calibre source test, but pushed the scale even smaller. A small geophone was epoxied to a outcrop of fractured diabase rock. A light tack hammer was used to create seismic waves in the rock. In addition to testing the characteristics of such a high frequency source (>2000 Hz), the project revealed some interesting featrues about how well energy propagates across cracks.
Rockland Cemetery site evaluation
Rockland Cemetery is the current resting place of Maurice Ewing, founder of the Lamont Observatory. While the mountainside grounds are lovely, shallow bedrock has been an issue as new sections of the property are developed. This study mapped the depth to bedrock under an area currently being considered for development. A multichannel seismic approach allowed the rough bedrock surface to be mapped without the expense and disruption of digging.