Heat flow in the western United States

Abstract

Between 1962 and late 1970, subsurface temperature measurements were attempted at more than a thousand drilling sites in the western United States. Temperatures from over 150 boreholes at about 100 distinct sites were suitable for estimates of the vertical geothermal flux. These results more than double the data from the western United States and confirm that heat flow is variable but generally high in this region. Within the over-all pattern of high heat flow, there are several distinct geographical regions, each occupying several hundred square kilometers, characterized by low-to-normal heat flow. Normal values were measured in the Pacific northwestern coastal region and the northwestern Columbia Plateaus. Additional results confirm the previously reported trend of very low heat flow in the western Sierra Nevada, increasing to normal near the crest of the range. The present work also confirms that heat flow is high in the northern and southern Rocky Mountains and somewhat lower in the central Rockies. The north-central part of the Colorado Plateau is a region of normal heat flow with higher values near its eastern border with the southern Rockies. The Basin and Range province as a whole is characterized by high heat flow that extends to within 10 to 20 km of the eastern scarp of the Sierra Nevada. The abrupt thermal transition between the Sierra Nevada and the Basin and Range province may occur partly in the Sierra Nevada physiographic province. Between Las Vegas and Eureka, Nevada, there is a large previously undetected zone of low-to-normal heat flow that is most probably the result of a systematic, regional water circulation to depths of a few kilometers. North of this zone, there is an area of several hundred square kilometers characterized by heat flows of 2.5 HFU (μcal/cm2 sec) or greater. In central California and adjoining western Nevada, a preliminary contour map suggests a heat-flow pattern with alignment parallel to the strike of the major geologic structures.