Press Release

Seismic Study of Ancient Cataclysm Begins

By SpaceRef Editor
October 4, 2004
Filed under , ,
Seismic Study of Ancient Cataclysm Begins

Note to Editors: Have a blast. Reporters are welcome to accompany and
film scientists in the field. Please call above for location and dates,
which are subject to the weather. We would appreciate your help in
notifying local residents that they may hear blasting or feel mild
shaking on Oct. 3-5.

What happens when a comet or asteroid more than a mile wide slams into
the Earth at supersonic speed? U.S. Geological Survey (USGS) scientists,
with help from students and professors from Virginia Tech University,
are about to find out as they begin a seismic survey of the
35-million-year old Chesapeake Bay impact crater.

Scientists began surveying on Sept. 20, and they expect to complete the
preparations on Oct 1. During the first few days of Oct., the USGS will
set off low-level underground blasts in a nearly 20-mile-long line in
Northampton County, Va. between the towns of Cape Charles and
Nassawadox, west of highway 13. They will also complete a second
higher-resolution survey about 2 miles long near Eyrehall Creek north of
Cheriton. Preparation for the high resolution survey will begin about
Oct. 7, with data collection expected a few days later.

“The seismic recordings will give us a look at the subsurface rock and
sediment layers, faults, and other structures produced 35 million years
ago by the Chesapeake Bay impact,” said USGS scientist Greg Gohn. “This
ancient event probably fractured bedrock to a depth of at least 5 miles.
These surveys will tell us more about the impact processes and products
and their effects on ground-water resources available today in the
southern Delmarva Peninsula.”

The project will involve 30 small explosions buried at depths of about
60 feet, and about 800 seismic-shotgun blasts at depths of about one
foot. As energy waves from the blasts travel through the ground they
will be recorded by portable seismometers placed throughout the area.
Because the ground motion being recorded is less than that caused by
normal daylight activities, such as vehicular traffic or vibrations from
pumps, most of the blasting and recording will be done at night, usually
between 10 p.m. and 3 a.m. over a 2 or 3 day period.

“We want to get the word out to those in the area that they might hear
blasting or feel mild shaking similar to that produced by a distant
quarry blast, so we are appealing to the local media for help in
notifying the public,” said Gohn. USGS and other scientific agencies
have completed seismic experiments like the one planned in Northampton
County in various parts of the U.S. and Canada for many years.

Scientist Rufus Catchings, who is with the USGS Western Region
Earthquake Hazards Team in Menlo Park, Calif., is leading the seismic
survey. He expects the high-resolution seismic imaging effort to locate
crater features to depths of about one mile, and the lower-resolution
survey to image structures to depths of more than 3 miles across a broad

The Northampton County seismic survey is part of a site characterization
study to determine the best location for a deep test hole that is
scheduled to be drilled into the central part of the crater in 2005.
Earlier phases of the characterization study included an electrical
conductivity survey in March of this year and a test hole that was
drilled to 2,700 feet at Cape Charles in May and June.

The USGS serves the nation by providing reliable scientific information
to describe and understand the Earth; minimize loss of life and property
from natural disasters; manage water, biological, energy, and mineral
resources; and enhance and protect our quality of life.

SpaceRef staff editor.