GEOTHERMAL RESOURCES

Geothermal resources are defined as the natural thermal energy within the Earth that can be used in economic competition with other forms of energy within the next few years. All of the thermal energy above surface temperature within the upper 6 miles of the Earth's crust, without regard to the economics of its production and use, is estimated to be about 32,000 billion-billion British thermal units. Most of this immense resource base is too diffuse to be extracted and used, but about 6.4 billion-billion British thermal units, the equivalent of 1.2 trillion or more barrels of oil, is judged to be a

resource.

The resource assessment presented in Circular 790, an updated assessment of U.S. geothermal energy resources which was published in fiscal year 1979, highlights two points. First, the total national geothermal resource is many times greater than the part that is being recovered and used today. Second, exploitation of geothermal energy is coming of age, as demonstrated by a recent increase from 7 to about 16 percent in the annual rate of growth of geothermal electrical capacity worldwide.

At present, the United States produces electricity from geothermal energy only at The Geysers in California, the world's fastest developing geothermal field. Installed electrical capacity there is now 660 megawatts, up from 500 megawatts at the end of fiscal year 1977. The Geysers development taps a vapor-dominated hydrothermal convection system. Pilot plants for generating electricity from hot-water convection systems, which are more numerous, are now in the planning or construction phase at Imperial Valley, Calif., Valles Caldera, N. Mex., Roosevelt Hot Springs, Utah, Raft River, Idaho, and Puna, Hawaii. The new national assessment notes that the total amount of energy contained in all hydrothermal convection systems that have temperatures hotter than 194 °F is about 9 billion-billion British thermal units. The

assessment notes further that about 25 percent (2.2 billion-billion British thermal units) of this, the equivalent of 430 billion barrels of oil, is recoverable.

The new assessment attempted a first evaluation of low-temperature geothermal waters (less than 90°C) that are suitable for direct use in space heating, agriculture, and industry. Current knowledge does not allow a quantitative estimate of the low-temperature resource. However, areas of potential low-temperature resources are outlined in Circular 790, and an extensive list of lowtemperature thermal springs and wells is tabulated, along with available data on water temperature and chemistry. The Geological Survey, in conjunction with the Department of Energy, Division of Geothermal Energy, and several State agencies, is continuing to study low-temperature resources, with the aim of producing a quantitative estimate of their magnitude in the near future. Examples of direct use of geothermal waters exist at Klamath Falls, Ore., where a large and growing proportion of buildings is heated by thermal waters that underlie much of the city, and at Boise, Idaho, where about 300 homes have been similarly heated throughout the 20th century.

About 0.4 to 4.2 billion-billion British thermal units of energy, equivalent to 75 to 780 billion barrels of oil, may be recovered from geopressured geothermal resources. The geopressured resources consist of thermal water and dissolved methane contained in the high-pressure aquifers of deep sedimentary basins, primarily in the northern Gulf of Mexico Basin. Much of the data available on this resource is by a byproduct of drilling for petroleum. The water is thought to be saturated with methane, which accounts for about one-half of the total energy available from such systems. The geopressured resource is clearly large and is the subject of continuing studies.

EARTHQUAKE SEQUENCE

The largest earthquake in the San Francisco Bay area in 68 years occurred August 6, 1979, at Coyote Lake, in a rural area 65 miles southeast of San Francisco. The earthquake, which measured 5.9 on the Richter scale, was felt over a large area but caused only minor damage because of its location in a relatively unpopulated area. The event was caused by sudden slip on the Calaveras fault, one of several large faults that branch from and lie parallel to the San Andreas fault in the bay area. This complex fault system, which marks part of the boundary between two large crustal plates, has been under intensive study by the Survey for many years. Nearly 600 devices that monitor earthquakes, magnetic fields, crustal straining and tilting, and slow fault offset are in operation in the bay area. In addition, extensive mapping programs have been carried out to identify active traces of major faults. Because fault movement on the Calaveras and San Andreas faults was anticipated, the region near Coyote Lake was one of the most densely instrumented in the world. Immediately after the event, more instruments were rushed to the area to supplement the existing networks, and searches for ground cracking and fault offsets with movement were begun. Thus, Survey scientists had the rare opportunity to record much useful data in the immediate vicinity of a potentially damaging earthquake, in an area that had been mapped geologically. Because of the quantity and quality of the data recorded, the earthquake will undoubtedly become a textbook example.

Records made during the earthquake and aftershock sequence will be analyzed to obtain information about the faulting process itself and about the effects of the earthquake, including the response of structures and foundations to strong ground shaking. The mass of the data accumulated by Survey personnel in the years before the event will be carefully examined for precursory phenomena; that is, any unexpected changes in the properties of the Earth that were related to the impending earthquake and might have value in predict

analysis of the data will require years of study, but much useful information has already been obtained.

More than 50 seismometers of the Central California Network were within 30 miles of the earthquake. These sensitive instruments recorded more than 1,000 smaller events (aftershocks) in the 15 days following the main shock and showed that ground rupture occurred over a vertical zone 12.5 miles long and from 2.5 to 7.5 miles wide. The earthquake sequence was found to be unusual in that the largest aftershocks were smaller than expected, considering the size of the main shock. This anomaly may reflect that fact that some of the accumulated strain on the Calaveras fault is released by slow steady slip (fault creep), or it may indicate that some accumulated strain has yet to be released. Understanding why larger aftershocks were relatively rare is important because, when large aftershocks do occur, they may cause failure in structures already weakened by a main shock.

Field searches for ground cracking, slumping, and fault offsets, undertaken within a few hours after the earthquake, revealed a complicated pattern of small cracks over zones from 30 to 300 feet wide. The amount of offset measured in the field was 0.5 inch or less, which was not as much as would be expected from an event as large as the Coyote Lake earthquake. The zone of disturbance generally coincided with the Calaveras fault, as it had been previously mapped, demonstrating that the criteria used to identify active faults were valid. The length of the disturbed zone was about 18 miles, somewhat longer than the aftershock zone. It is not clear how much of the observed ground disturbance was due to rapid fault motion occurring during the earthquake and how much was due to shaking, slumping, and postearthquake slip.

The Calaveras fault, along with certain other faults in central California, displays fault creep, that is, the fault does not slip just during earthquakes, but rather it slips slowly at various points by a small amount from time to time. This more or less steady slip along the fault is responsible for releasing accumulated strain on some portions of the fault and may cause increased strain on portions that do not creep. The cumulative surface deformation caused by fault

creep is used to determine the locations of creeping sections of the fault, and measuring devices are placed across the fault in these areas to measure the effect of individual creep events. A device of this type had been in operation near the southeastern end of the Coyote Lake rupture for several years preceding the earthquake. The records show that creep events ceased at that site 4 years before the earthquake. There is evidence of a similar decrease in creep rate before other earthquakes, and this sort of creep behavior will be carefully studied to see if it has predictive value.

The very strong shaking that occurs in the immediate vicinity of larger earthquakes usually overloads ordinary seismometers, and specially designed strong-motion instruments are required to obtain complete records of the shaking. Strong-motion records are of fundamental value in engineering design of buildings, dams, and other structures in seismically active areas. Because records of strong ground motion must be made near the source of an earthquake and because large earthquakes are relatively rare events, few strongmotion instruments have been in operation directly above sizable earthquakes. However, an entire array of such instruments, placed by the Geological Survey and the State of California, was recording during the Coyote Lake earthquake. Records of strong motion were obtained not only at the ends of the rupture zone but also along a line of instruments that started at the center of the rupture zone and extended 6 miles away from it. Forces as high as 40 percent of the force of gravity were recorded at sites near the rupture zone. These values fell to 25 percent a few miles away from the fault and decreased to negligible values at greater distances. The pattern of strength and frequency of shaking showed that the earthquake started at the northwest end of the rupture zone and that the break moved to the southeast. Because 80 aftershocks were recorded at 3 or more strong-motion recording sites, a description of fault failure during the main event can probably be worked out in considerable detail. The knowledge gained will be of value in predicting the character of strong ground motion near other faults and is expected to have an impact on engineering practices in areas subject to seismic hazard.

COAL FOLIOS

An important part of the Geological Survey's coal program is to organize, to compile, to evaluate, and to synthesize existing and new coal-resource-related information in the form of coal folios. This coal folio program provides information to BLM's land use planning activities and Resource Management Plan (RMP) for Federal land, and, therefore, it is closely tied to the Department of the Interior's Federal Coal Leasing Program. The Office of Surface Mining, Department of the Interior, requires folio-related information to fulfill its regulatory functions. State and local governments have become interested in the coal folio program because it provides the information they need to evaluate Federal plans and to plan for coal development within their jurisdictions.

A coal folio generally consists of maps (scale 1:100,000), other graphics, and supplemental text material. These materials present information related to the quantity and quality of coal resources and environmental geologic factors needed to assess potential utilization and reclamation of disturbed land after the coal has been mined. Information usually is presented on a topographic base map and published in the Coal Map (C-) Series. Related maps are published as each is completed. The folio format will vary according to the information required and available in different coal-bearing areas. For example, a folio for one area may include a separate map for each of the following topics: bedrock geology, including principal coal beds; surficial geology, with notations on the composition and physical properties of surface materials; detailed interlocked cross sections that establish the stratigraphic framework of the coal-bearing rocks; structure contours on the top or base of principal coal beds; isopach maps displaying thickness of principal coal beds; isopach maps of the overburden for the principal coal beds; estimated coal resources categorized according to Geological Survey standards; potential and actual geologic hazards that should be considered during coal-development planning; patterns of land-surface and mineral-right ownership; hydrologic and climatologic data; and other available and necessary coal-related information. A folio for a different area might include additional or fewer information components. In addition to the component elements of the folios, a wide range of supporting and derivative reports consisting of information not suited for graphic portrayal is commonly prepared.

Regional coal-resource assessment studies are being conducted in areas covered by 24 1:100,000-scale

(0.5° x 1°) quadrangles in the coal-bearing western part of the United States, and coal-related environmental geology studies are underway in areas covered by 73 1:100,000-scale quadrangles. In most cases, the whole area of a quadrangle will be studied-a 1:100,000-scale quadrangle covers more than 1,600 square miles, an area equal to 32 7.5-minute quadrangles; in other cases, only the coal-bearing part of the quadrangle has been or will be examined. The work presently planned, underway, and completed will result in a minimum of 60,000 square miles of mapping at 1:100,000 scale.

The evaluation of subsurface data is critical to the regional coal-resource-assessment program. This subsurface data is obtained by core-drilling in areas being considered for inclusion in the Federal Coal Leasing Program and where existing oil, gas, and water wells are either improperly located or were not adequately cored or logged. A total of about 90,000 feet of coal exploratory drilling was done in fiscal year 1979 to obtain samples for coal quality information, geotechnical testing for engineering data, establishment of local and regional geochemical baselines, determination of methane content of coals, study of rocks associated with coals, and many other purposes; about 3,000 feet of core samples were obtained.

Much information is obtained from geophysical logging of oil and gas test wells, water wells, and geophysical exploration drill holes. Some of the data derived from this logging are natural radioactivity measurements and density measurements. A total of more than 110,000 feet of various drill holes were logged geophysically in fiscal year 1979.

The results of this research are published as quickly as possible, so that they can be used by planners, mining and development industries, geoscientists, and all persons concerned with the safe and orderly development of the Nation's energy resources.

During fiscal year 1979, Survey geologists produced 23 coal-related and 246 environmental geologic maps, 30 coal reports and 24 environmental reports, and 12 coalrelated and 8 environmental abstracts for scientific talks. Coal folios covering three quadrangles, the Kaiparowits Plateau (Utah) and Recluse (Wyoming) areas, were completed in fiscal year 1979. Maps and reports that contribute to 20 other folios were completed. Three folio areas in the southern Wasatch Plateau, Utah, were completed prior to fiscal year 1979. The index map shows the locations of completed folios, those partly completed, and areas of work in progress in fiscal year 1980.

Effective management of water resources requires that up-to-date scientific hydrologic information be readily available for planners and managers. The Water Resources Division has the principal responsibility within the Federal Government for providing hydrologic data and appraising water resources to facilitate evaluation of water problems. The Division's program is designed to present impartial accurate data and scientific analyses. It supplies reports and maps to the public in Federal, State, and local publications; in technical journals; and through selected libraries.

The U.S. Geological Survey provides extensive support to the missions of other Federal agencies and, under the Federal-State Cooperative Program, to State and local agencies. In this way, the Survey keeps abreast of waterinformation needs at all levels of government and develops programs responsive to those needs. Through a network of offices (see page 78) in all 50 states, as well as in Puerto Rico and Guam, close communication is maintained with State and local agencies.

A major responsibility was assigned to the Survey in 1964 when it was designated the lead agency for coordinating water-data-acquisition activities of all Federal agencies, including information on streams, lakes, reservoirs, estuaries, and ground water. This coordination effort minimizes duplication of data collection among Federal agencies and strengthens the overall data base and its accessibility.

THE FEDERAL PROGRAM

The water-data collection, resource investigation, and research activities of this program are carried out in areas where the Federal interest is para

mount. These include bodies of water in the public domain, river basins and aquifers that cross State boundaries, and other areas of international or inter-State concern. Activities include

operation of surface- and ground-water quantity and quality measurement stations throughout the country, the Survey's Central Laboratories System, hydrologic research and analytical studies, and a variety of supporting services.

THE FEDERAL-STATE

COOPERATIVE
PROGRAM

Geological Survey programs have multiple objectives and serve the earth science and related information needs of a large number of government agencies and private groups. As major users of this information, State, regional, and local agencies have an important role in helping to define the scope of Survey programs. Accordingly, selected projects judged to be of mutual benefit to the Federal, State, and local governments are funded on a 50-50 basis in the Federal-State Cooperative Program.

In fiscal year 1979, the Water Resources Division joined in cooperative programs with 590 State and local agencies; much of the work was done by the Survey, but State and local agencies provided half the funds. The current work on developing a water-use data base in the Cooperative Program is being done by the States.

Through contact with those involved in water conservation, development, management, and use, the Water Resources Division anticipates and responds to changing priorities. Planning the annual program in each State is a mutual decision, with the Survey representing national interests and the cooperating agencies representing State and local interests. As the need arises for additional and new kinds of water information, programs are adjusted within the framework of the work is problem oriented and interpriorities and resources. As a result, disciplinary. The diverse program activities include collection of long-term multipurpose data (surface water, ground water, water quality, and water use); special interpretive studies of the physical, chemical, and biological characteristics of water; and appraisals for environmental impact evaluation, energy development,

coastal zone management, subsurface waste storage, waste utilization, land use planning, flood plain management, and flood-warning systems.

The strength of the Federal-State Cooperative Program lies in (1) coordinated programming for water information that responds to identified and developing needs of people at all levels and relates to the environmental aspects of water use, (2) the quality and acceptability of the water data accumulated through uniform programs in 50 States and several of the territories, and (3) the nonadvocacy position of the Geological Survey in carrying out and reporting on its work.