Stanford geologists present preliminary findings

Special to the Modoc County Record

July 7, 2005

By Patricia Hensley

A group of geologists from Stanford University and representatives from a team working with the US Geological Survey (USGS) out of Denver met with interested folks in Cedarville on June 23 for a lively lecture some humorously dubbed "Seismic Geology 101".

The event was sponsored by the Greater Surprise Valley Chamber of Commerce. It included a presentation of preliminary findings from a series of experiments conducted in the region last summer as well as an overview of two recent projects which concluded in late June.

The Stanford team was in the area to conduct detailed geologic mapping in specific areas of the Warner Mountains. Older geologic maps of the area are too simplistic to be of use in the team's ongoing projects.

Anne Egger, the Undergraduate Program Coordinator and Lecturer in the Department of Geological & Environmental Sciences, said the finished maps will "tie in to what we're seeing below the surface as we chart the faults and types of rocks visible on the surface. Existing maps are unsatisfying for us at this point. We want to add more detail to them." The team is also collecting samples to have processed in their labs at the university.

Presenting a detailed update on one of their last evenings in the valley was in many ways a "thank you" to community members who have shown an enthusiastic interest in the ongoing work of the scientists. "We've run into many people as we hike about", said Egger. "We all want to thank everyone who has helped us: the BLM and Forest Service, Modoc County Roads Department, and the fairgrounds staff. Everyone we've encountered has been friendly and helpful. We hope to be able to come back soon!"

The team, headed by Professor Elizabeth Miller, Dr. Joseph Colgan (who will join the USGS in Menlo Park in the fall), and Egger, brought along a wide variety of local geologic maps and fault maps for people to inspect. Colgan also passed around a core sample contributed by drillers working on a geothermal project near Lake City.

The heavy rock "cylinder", collected at 4,020 feet under the valley's sedimentary layers, revealed a colorful conglomerate of pebbles indicating it may have once been part of an ancient river channel. Though he called the core "interesting and beautiful", Colgan contrasted what it revealed with the way geologists can now "see" much deeper under the earth's crust using man-made seismic waves. Even the deepest drilling samples can't answer basic questions geologists are beginning to ask about the area. Apart from monitoring occasional earthquakes, creating and then recording the behavior of induced seismic waves promises to yield a much clearer understanding of the geologic forces at play under the mountains and valleys in the region. "We 'look' at the boundary where the solid crust meets the earth's molten mantle by studying the generated sound waves", said Colgan. "As we understand the behavior of the waves and begin to create a high-resolution image of the geologic formations under Surprise Valley and beneath the crust, we can surmise what the earth's interior looks like."

Colgan, who recently wrote his doctoral thesis on the "Basin and Range" topography which begins at the Warners and stretches east to the Wasatch Range in Utah, explained how the previous experiments conducted in the area allow geologists to get a much fuller picture of the forces that shaped Surprise Valley and the geologically fascinating region east of the valley.

Last September, Colgan's team set off a succession of precisely timed explosions along a 270-kilometer line stretching from north of Winnemucca to west of Canby. The seismic waves created were recorded and stored on computer chips set in receivers known as "texans".

"The waves from our explosions went 20 miles deep. The biggest variation we saw was right under Cedarville", he said. "We saw down to the base of the crust and even into the mantle. We got a nice data set out of it all!"

A second phase of experiments was carried out within Surprise Valley. A massive truck dubbed "T-Rex" was used to send vibrations deep into the earth along 49 Lane north of Cedarville. Texans were again used to record the sound waves.

Part of the experiment's value was determining that the 60,000-pound vibrator truck, previously only used commercially to explore for underground oil deposits, worked well for the purely "theoretical" application. University students are still processing the data from the T-Rex experiments, Colgan reported.

The Surprise Valley area is increasingly interesting to scientists studying what Miller characterized as the "corrugated topology" known as the "Basin and Range Geomorphic Province" which appears to end at the Warner Mountains. "To the west of the Surprise Valley boundary, the crust is smoother, not as stretched out and thinned as what we see in the Basin and Range area", said Professor Miller.

"This area is fast becoming the new "Geologic Mecca" of California!" BLM Geologist Ken Collum who works out of the Surprise Field Office in Cedarville, mentioned that archeological, paleontological and geologic groups from the University of Nevada, Reno, Utah State, Chico State, Stanford, and UC Berkeley have been working in the area within the past few weeks, an unprecedented phenomenon which reinforces Miller's observation that the heretofore understudied region has been "discovered".

Miller, Egger, Colgan and a group of undergraduate students were joined at the community presentation by Drs. Tony Crone and Stephen Personius also happened to be working in the area at the same time as the Stanford team. Their group of paleoseismologists, affiliated with the USGS, is studying the Surprise Valley Fault which runs along the base of the Warner Mountains.

After digging a deep trench across the fault north of Cedarville on property owned by Dr. Jim and Denise Harrower, the scientists began mapping and taking samples from the exposed layers they believe represent past seismic events along the fault. Crone caused a few shivers in the audience when he announced the valley's largest fault "runs about a half-mile west of here, paralleling your Main Street." "Our suspicions are the SV Fault is one of the more active faults in the region that stretches from the Wasatch Mountains to the Pacific", said Crone. "The best way for us to collect information and interpret past movement is to study a cross section of the fault."

The team dug "as deep as we comfortably could", using a backhoe to reach a uniform depth of about 20 feet. They mapped the deposits exposed in the trench, though for now their painstaking field work raises more questions than it answers. "It's like working with pieces of an incomplete puzzle. We have to fill in a lot of blanks", said Crone. The team is collecting samples to analyze later though they did pass around scrapings from an unusually thick layer of volcanic ash discovered at about 17 feet deep. "The ash may be from Mount Mazama which erupted over 7,000 years ago", said Crone. It will be analyzed and compared with known deposits from the colossal explosion that created Crater Lake.

While Egger and the others peppered their discussion with many questions they hope to answer after further experiments, each will be sharing their findings with an ambitious project dubbed "EarthScope"

EarthScope is a national science initiative to explore the structure and evolution of the North American continent and to understand the physical processes controlling earthquakes and volcanoes.

With approximately $200 million in funding from the National Science Foundation, geologists from the USGS and universities such as Stanford are joining together to systematically monitor and study the earth's interior. They will deploy an array of equipment that includes seismometers, strainmeters, and GPS receivers across the US.

"EarthScope is the largest systematic survey of the continent funded by Congress since the Lewis and Clark Expedition 200 years ago", say project organizers.

All of EarthScope's data will be freely and openly available to the scientific community as well as to teachers, students and the general public. The public can follow the national progress of the project at the website www.earthscope.org.