Connections

Many other scientists are working in the Warner Range - Surprise Valley region as well, and we have had the opportunity to connect with them in the field and beyond. In particular, we benefitted significantly from interactions with a USGS paleoseismology project and a geothermal drilling project.

Paleoseismology

A team of scientists from the USGS Earthquakes Hazards Program is working to understand the paleoseismology, or earthquake history, of the Surprise Valley fault. Documentation of prehistoric earthquakes is necessary because the recorded history of earthquakes in the region is so short (<150 years). This study has four objectives:

• Identify evidence of geologically recent (last 100,000 years) prehistoric earthquakes
• Determine the age of the earthquakes
• Estimate the size (magnitude) of the earthquakes
• Gauge the level of activity on the fault

All of these objectives help to provide a sense of the seismic hazard associated with the fault. The main technique they use to acquire paleoseismological data is trenching the fault itself. During the summer of 2005, we visited the trench they dug a few miles north of Cedarville.

A Quaternary scarp along the Surprise Valley fault (steep, shaded area in middle ground; blue line marks base of the scarp). The red line shows where the trench was dug. Photo courtesy Steve Personius, USGS.Photo courtesy Steve Personius, USGS.	Students from Stanford in the trench with USGS scientists. The tree in the upper right is the same tree in the upper right of previous photo. Photo courtesy Anne Egger.

After trench excavation, the team identifies and maps exposed faults and deposits, determines the origin and processes that formed these features, and infers the geologic events that produced them. The final step is locating and sampling materials for radiometric dating, in order to interpret the timing of prehistoric earthquakes.

The trench exposed a steeply east-dipping normal fault, which places hillslope-derived colluvial debris against thinly-bedded lake sediments. Along this fault, the Warner Range is being uplifted while the Surprise Valley is sinking. The lake sediments record the periodic filling of the valley with water during the last Pleistocene glaciation about 15,000-20,000 years ago. All together, this information will be used to determine the size and timing of large prehistoric earthquakes along the fault, and the potential for future seismic hazards in the region.
	USGS scientist Anthony Crone maps layers of lake sediments and colluvium. Photo courtesy Anne Egger.	The Surprise Valley fault as exposed in the trench. The gray layers on the right are lakebed sediments; the brown material is colluvium. Photo courtesy Anne Egger

The scientists involved in the trenching project are Steve Personius, Anthony Crone, Michael Machette, Dave Lidke, and Lee-Ann Bradley. The Surprise Valley Fault investigation is part of a larger project on seismic hazards in the Intermountain West.

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Geothermal drilling

The Surprise Valley region hosts a number of hot springs, suggesting that the area might be a feasible source of geothermal energy. The eruption of a mud volcano in the northern part of the valley in 1951 launched a series of geothermal investigations that continue today. During the summer of 2005, Lake City Geothermal, LLC, drilled a core in the Lake City geothermal field, directed by Dick Benoit, a geothermal energy consultant.

Lake City is located about 15 miles north of Cedarville in the Surprise Valley and is at the very bottom of the map shown to the left. The hottest part of the geothermal field is about 2 miles north of Lake City and is marked by a series of hot springs at the surface (blue squares) and a snowmelt line in the winter. In 2005, the LCSH-5 temperature gradient well was drilled to a depth of 4720 feet below the surface. Much more information about the results of this and other geothermal exploration in the Surprise Valley can be found in these publications: Overview of the Lake City Geothermal System (2004) Dick Benoit, Colin Goranson, Steve Wesnousky, and David Blackwell (PDF) Core Hole Drilling and Testing, Lake City, California Geothermal Field (2005) Dick Benoit, Joe Moore, Colin Goranson, and David Blackwell (PDF)

Map and legend are modified slightly from Figure 1 of Benoit et al, 2005, and was provided courtesy of Dick Benoit.

We had the opportunity to examine the core extracted from LSCH-5, extending our geologic information deep below the surface. There is more information about the core in the geology section of this web site.

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