New Technology for Tracking Ancient Earthquakes
Inserting the Geoslicer into the trench at Tule Pond (Tyson Lagoon), Hayward fault, Fremont, CA. photo by Jennifer Adleman, USGS.
Recently, two new techniques have been introduced that supplement the basic trenching method. First, peeling helps preserve the information revealed in the trench by actualy removing the trench face, much the way the paint is sometimes pulled off a wall with old tape. When a peel is removed, the reading of the geologic strata in the trench walls can continue long after the trench is closed.
Taking a peel of the trench at Tule Pond (Tyson Lagoon), Hayward fault, Fremont, CA. photo by Jennifer Adleman, USGS.
Next, to extend the depth of a trench study (which extends the historical period available for study), geologists utilize a new device called Geoslicer, invented by Takashi Nakat of Hiroshima University. This device can reveal faulting in the deeper, water-saturated sediments found below the water table, where geologists cannot safely trench.
On Tuesday October 2, 2001 Japanese scientists from the Geological Survey of Japan and Hiroshima University and American scientists from the U. S. Geological Survey removed a peel from one of the walls of a trench excavated the previous week. Using a rubberized epoxy compound, scientists peeled and removed the south face of the trench at Tule Pond. A series of photos take you through this peel process at the Tule Pond site.
Finally, on Wednesday, October 3, at the same location, the Japanese and American scientists demonstrated the Geoslicer, a large, crane-operated device designed and built in Japan. The Geoslicer can cut an additional section 12 feet deep (relative to the bottom of the10-foot-deep trench) into the geologic deposits, and bring it, intact, to the surface for study. The Geoslicer allows the geologists to sample below the water table. By extending the depth, the Geoslicer extends the length of the earthquake history available for study. A series of photos takes you through the work done with the Geoslicer at the Tule Pond site.
The Geoslicer travels across the country
The Japanese team next brought the Geoslicer to the New Madrid seismic zone. In conjunction with the USGS, seven samples from a liquefaction site near Blytheville, Arkansas were pulled out on October 22nd.