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Continental scientific drilling is an important tool for exploring natural and anthropogenic processes on Earth. In past decades the results obtained from lake drilling projects contributed significantly to a better understanding of short-term and long-term climate change and natural hazards.

[1] Workshop on Deep Scientific Drilling to Study Reservoir Triggered Earthquakes; Koyna, India, 21–25 March 2011; The Koyna region in western India is a classical site of reservoir-triggered seismicity in an intraplate setting. Triggered earthquakes have been occurring in a restricted area of 20 × 30 square kilometers since the impoundment of Shivajisagar Lake in 1962; these include the largest triggered earthquake of M ∼ 6.3 on 10 December 1967, 21 earthquakes of M ≥ 5, about 200 earthquakes of M ∼ 4, and several thousand smaller earthquakes. There is no other source of seismic activity within a radius of 50 kilometers from the Koyna region. The shallow (4- to 6-kilometer) occurrence of moderate size earthquakes in this region makes it an ideal site for deep drilling to study earthquake processes and the mechanics of faulting in an intraplate zone.

Ocean Drilling Program (ODP) Hole 1256D, drilled 500 m into oceanic basement in the Guatemala Basin, is the first hole prepared with the infrastructure desirable for drilling a moderately deep hole into the oceanic basement (1.5–2 km). A second ocean drilling leg to this site should finish the recovery of the first complete section of upper oceanic crust from lavas down through the dikes into the upper-most gabbros. Although Site 1256 has many advantageous features for a program to drill to the mantle, planning such an operation now would be premature, due in part to lack of engineering experience. In addition, there is significant scientific knowledge to be gained from drilling to depths of 1–3 km. Only through the characterization of the heterogeneity of the ocean crust by moderate-depth drilling at this and other sites will the essential information necessary to even choose a location for a full crustal penetration be acquired. The information learned on the “road to” selecting a MoHole site is at least as important as succeeding with that inspirational goal itself [see also Murray et al, 2002].

A new initiative for drilling and coring directly into the San Andreas fault at depths up to 10 km is being proposed by an international team of scientists led by Mark Zoback, Stanford University; Steve Hickman and Bill Ellsworth, U.S. Geological Survey; and Lee Younker, Lawrence Livermore Laboratory. In addition to exhuming samples of fault rock and fluids from seismogenic depths, the hole will be used to make a wide range of geophysical measurements within the fault zone and to monitor the fault zone over time. Four areas along the San Andreas have been selected as candidates for deep drilling: the Mojave segment of the San Andreas between Leona Valley and Big Pine, the Carrizo Plain, the San Francisco Peninsula between Los Altos and Daly City, and the Northern Gabilan Range between the Cienga winery and Melendy Ranch. These sites were chosen from an initial list compiled at the International Fault Zone Drilling Workshop held in Asilomar, Calif., in December 1992 and at meetings held this winter and spring in Menlo Park, Calif.

The international Ocean Drilling Program (ODP) and the Continental Deep Drilling Program of the Federal Republic of Germany (KTB) are large exploration projects in which core-calibrated borehole measurements play an important scientific role. In the organizations that run both projects, separate working groups are responsible for planning the borehole logging program, supervising the downhole operations, stimulating the research and development of interpretation methods, and initiating new tool designs and developments. These groups came together September 13–15, 1989, for a meeting at the KTB drill site laboratory in Windischeschenbach, Oberpfalz, FRG. Conveners were Ralph Hanel (NLfB, Hannover, FRG) and Paul F. Worthington (BP Research Centre, Sunbury-on-Thames, U.K.) About 50 scientists attended. They agreed that integrated working groups be established, through which the two programs could collaborate even more closely in borehole logging.

The initial responses from OMB, Congress, and industry have been overwhelmingly positive in support of a proposed major drilling program along the U.S. offshore coastal areas in deep water. The extensive sedimentary deposits located along the U.S. continental slopes are, as yet, unexplored. There have been numerous suggestions that there is a significant potential for extensive reserves of hydrocarbons, but these suggestions are largely speculative. At the same time, there is a great amount of scientific interest in the geology of the continental margins, so it has been logical in recent months to propose a combined scientific and commercial study offshore. Such a proposal is being made to Congress by the National Science Foundation for the purpose of obtaining funds to convert the government-owned Glomar Explorer (the ship that was originally built for the use of the C.I.A.) into a vessel capable of performing deep drilling operations and for other costs of running the program over the next 10 years. Industry is being approached to contribute 50% of the costs.

Long Valley caldera has been explored for its potential geothermal resources for at least two decades. Unocal Geothermal drilled two deep test wells on the resurgent dome of the caldera during 1979. Neither of these wells encountered a deep, high temperature geothermal reservoir. The results from these wells and other geologic data focused exploration on the western caldera moat. Encouraging temperature gradient data in 1982 led to the drilling of a deep test well in 1985. That well, IDFU 44-16, encountered deep temperature reversals and a sequence of rocks unlike the previous penetrations on the resurgent dome. Evidently the well is still within the ring fracture system of the caldera and not within a central, upwelling, hydrothermal system which supplies the caldera’s discharge. 9 refs., 8 figs.

Earthquakes, ground uplift, and increased hydrothermal activity are only the most recent examples of the intense tectonic and volcanic activity that has occurred at Long Valley caldera, Calif., over the last 3 million years. A large number of geophysical experiments, conducted by several hundred investigators over the past few years, clearly indicate that a major body of magma exists within the central part of the caldera at drillable depths of 4–5 km. Plans are underway to drill toward and eventually into this magma body.

A Continental Scientific Drilling Project (CSDP) Workshop, attended by 87 scientists, focusing on the Valles caldera was hosted by the Department of Energy and the Los Alamos National Laboratory, on October 5–7, 1982, in Los Alamos, New Mexico. The caldera, a large, Quaternary magmahydrothermal system, lies at the intersection of the Rio Grande rift and the Jemez lineament in north-central New Mexico and is a prime site for the first deep drill holes. One major objective of CSDP is to develop a broad scientific understanding of the roots of an active hydrothermal system associated with recent igneous intrusion. Surface geological, geophysical, geochemical, and hydrological data, along with information from shallow exploratory drillholes, will be used in the process of interactive development and testing of models and hypotheses for such systems. Ultimately, deep drilling will be essential to provide direct sampling of fluids and rocks at depth and to measure directly the critical in situ physical parameters. Thus, deep drilling research becomes an integral and necessary component in the synthesis, refinement, and verification of three-dimensional models of hydrothermal-magma systems and processes.

Plans for continental scientific drilling, supported by the National Science Foundation (NSF) through the DOSECC consortium of universities have been given a new direction as a result of the failure of the NSF budget to reach expected levels. Very deep drilling will not be initiated for some time because of its high cost, but an active program of drilling to depths of 1–5 km is being developed in its place. For the next several years, DOSECC (Deep Observation and Sampling o f the Earth's Continental Crust, Inc.) will focus on proposals for drilling experiments to improve our understanding of dynamic processes in the shallow crust. As a result of this change in emphasis, there is now an opportunity to propose experiments of this kind and to have them accepted for drilling over the course of the next few years.