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Mark D. Zoback

Publications and source records attributed to Mark D. Zoback.

At least 19 recordsLinked to original sources
USGS2022

State of stress in areas of active unconventional oil and gas development in North America

In this paper, we present comprehensive data on stress orientation and relative magnitude in areas throughout North America where unconventional oil and gas are currently being developed. We find excellent agreement between maximum horizontal principal stress (S Hmax ) orientations over a wide range of depths, using multiple methods. In all basins studied, we observed coherent stress fields that in some cases vary systematically from one part of a basin to another. In the Appalachian Basin in the eastern United States, S Hmax is oriented northeast–southwest to east-northeast–west-southwest and the style of faulting is compressive, transitioning from reverse faulting in eastern Pennsylvania and New York to principally strike-slip faulting in western Pennsylvania, Ohio, and West Virginia. In the midcontinent, central Oklahoma is characterized by an approximately east–west S Hmax direction and strike-slip faulting. The Fort Worth Basin in northeastern Texas is characterized by normal–strike-slip faulting and a north-northeast–south-southwest S Hmax direction. In the Midland subbasin of western Texas, S Hmax is consistently approximately east–west and normal–strike-slip faulting is observed. Farther west, the Delaware subbasin of western Texas and southeastern New Mexico is characterized by normal faulting and S Hmax rotates ∼150° clockwise from north to south. Marked changes in S Hmax direction also occur across the Raton Basin of southern Colorado and northern New Mexico, the Denver-Julesburg Basin in northern Colorado, and the Uinta Basin in northeastern Utah, likely associated with their location near the margins of extensional provinces. The new data sets we present help improve operational efficiency by constraining absolute stress magnitudes and the ideal azimuth to drill horizontal wells (i.e., perpendicular to the local S Hmax orientation) and make it possible to predict which fractures and faults are likely to be activated during hydraulic stimulation.

AAPG Bulletin↗
USGS2012

Hydraulic fracturing in situ stress measurements to 2.1 km depth at Cajon Pass, California

Stress measurements to 2.1 km reveal stress changes with depth that cannot be explained by an elastic response to uniform crustal strain. The data at about 1 km depth suggest that the stress is limited by the frictional strength of rock and is perturbed at greater depths by faults which intersect the borehole. The stress data indicate that there is little or no right-lateral shear stress acting on planes parallel to the San Andreas fault.

Geophysical Research Letters↗
USGS2012

In situ studies of velocity in fractured crystalline rocks

A study of the effects of macroscopic fractures on P and S wave velocities has been conducted in four wells drilled in granitic rock to depths between 0.6 and 1.2 km. The effect of macroscopic fractures is to decrease both V p and V s and increase V p / V s . In wells with a relatively low density of macroscopic fractures, the in situ velocity is similar to that of saturated core samples under confining pressure in the laboratory, and there is a clear correlation between zones with macroscopic fractures and anomalously low velocities. In wells with numerous macroscopic fractures, the in situ velocity is lower than that of intact samples under pressure, and there is a correlation between the rate at which in situ velocity increases with depth and the rate at which the velocity of laboratory samples increases with pressure. Differences in in situ P wave velocity between wells cannot be explained solely by differences in the degree of macroscopic fracturing, thus emphasizing the importance of composition and microcracks on velocity. In one highly fractured well the in situ P wave velocity is essentially the same for frequencies ranging from 10 Hz to 20 kHz; this suggests that the macrofractures affect velocity similarly over a broad frequency range. Chemical alteration of rock adjacent to macroscopic fractures appears to play an important role in reducing in situ velocities. Synthetic reflection seismograms generated from the velocity logs suggest that fracture zones are one possible source of deep-crustal reflectors observed on seismic reflection profiles.

Journal of Geophysical Research Solid Earth↗
USGS2012

In situ stress, natural fracture distribution, and borehole elongation in the Auburn Geothermal Well, Auburn, New York

Hydraulic fracturing stress measurements and a borehole televiewer survey were conducted in a 1.6‐km‐deep well at Auburn, New York. This well, which was drilled at the outer margin of the Appalachian Fold and Thrust Belt in the Appalachian Plateau, penetrates approximately 1540 m of lower Paleozoic sedimentary rocks and terminates 60 m into the Precambrian marble basement. Analysis of the hydraulic fracturing tests indicates that the minimum horizontal principal stress increases in a nearly linear fashion from 9.9±0.2 MPa at 593 m to 30.6±0.4 MPa at 1482 m. The magnitude of the maximum horizontal principal stress increases in a less regular fashion from 13.8±1.2 MPa to 49.0±2.0 MPa over the same depth range. The magnitudes of the horizontal principal stresses relative to the calculated overburden stress are somewhat lower than is the norm for this region and are indicative of a strike‐slip faulting regime that, at some depths, is transitional to normal faulting. As expected from the relative aseismicity of central New York State, however, analysis of the magnitudes of the horizontal principal stresses indicates, at least to a depth of 1.5 km, that frictional failure on favorably oriented preexisting fault planes is unlikely. Orientations of the hydraulic fractures at 593 and 919 m indicate that the azimuth of the maximum horizontal principal stress at Auburn is N83°E±15°, in agreement with other stress field indicators for this region. The borehole televiewer log revealed a considerable number of planar features in the Auburn well, the great majority of which are subhorizontal (dips < 5°) and are thought to be bedding plane washouts or drill bit scour marks. In addition, a smaller number of distinct natural fractures were observed on the borehole televiewer log. Of these, the distinct steeply dipping natural fractures in the lower half of the sedimentary section at Auburn tend to strike approximately east‐west, while those in the upper part of the well and in the Precambrian basement exhibit no strong preferred orientation. The origin of this east‐west striking fracture set is uncertain, as it is parallel both to the contemporary direction of maximum horizontal compression and to a late Paleozoic fracture set that has been mapped to the south of Auburn. In addition to these planar features the borehole televiewer log indicates paired dark bands on diametrically opposite sides of the borehole throughout the Auburn well. Processing of the borehole televiewer data in the time domain revealed these features to be irregular depressions in the borehole wall. As these depressions were consistently oriented in a direction at right angles to the direction of maximum horizontal compression, we interpret them to be the result of stress‐induced spalling of the borehole wall (breakouts).

New York↗
USGS2012

Well bore breakouts and in situ stress

The detailed cross-sectional shape of stress induced well bore breakouts has been studied using specially processed ultrasonic borehole televiewer data. Breakout shapes are shown for a variety of rock types and introduce a simple elastic failure model which explains many features of the observations. Both the observations and calculations indicate that the breakouts define relatively broad and flat curvilinear surfaces which enlarge the borehole in the direction of minimum horizontal compression. Refs.

Journal of Geophysical Research↗
USGS2012

Crustal strain near the Big Bend of the San Andreas Fault: Analysis of the Los Padres-Tehachapi Trilateration Networks, California

In the region of the Los Padres-Tehachapi geodetic network, the San Andreas fault (SAF) changes its orientation by over 30° from N40°W, close to that predicted by plate motion for a transform boundary, to N73°W. The strain orientation near the SAF is consistent with right-lateral shear along the fault, with maximum shear rate of 0.38±0.01 μrad/yr at N63°W. In contrast, away from the SAF the strain orientations on both sides of the fault are consistent with the plate motion direction, with maximum shear rate of 0.19±0.01 μrad/yr at N44°W. The strain rate does not drop off rapidly away from the fault, and thus the area is fit by either a broad shear zone below the SAF or a single fault with a relatively deep locking depth. The fit to the line length data is poor for locking depth d less than 25 km. For d of 25 km a buried slip rate of 30 ± 6 mm/yr is estimated. We also estimated buried slip for models that included the Garlock and Big Pine faults, in addition to the SAF. Slip rates on other faults are poorly constrained by the Los Padres-Tehachapi network. The best fitting Garlock fault model had computed left-lateral slip rate of 11±2 mm/yr below 10 km. Buried left-lateral slip of 15±6 mm/yr on the Big Pine fault, within the Western Transverse Ranges, provides significant reduction in line length residuals; however, deformation there may be more complicated than a single vertical fault. A subhorizontal detachment on the southern side of the SAF cannot be well constrained by these data. We investigated the location of the SAF and found that a vertical fault below the surface trace fits the data much better than either a dipping fault or a fault zone located south of the surface trace.

Journal of Geophysical Research Solid Earth↗
USGS2011

Deep scientific drilling in the San Andreas Fault Zone

A deep scientific drilling experiment in San Andreas fault zone would provide data essential to understanding the structure, composition, mechanical behavior, and physical state of an active, major plate-boundary fault. Toward this end, we are working with an international team of scientists and engineers to propose a long-term, integrated program of surface-based geological and geophysical investigations and deep drilling along the San Andreas fault system. Prior to drilling, a suite of comparative geodynamic models will be developed incorporating detailed investigations of geology, crustal structure, geophysical environment, hydrology, seismotectonics, and fault-movement history at each of the candidate sites. These studies will have a major impact on our understanding of the structure and physical properties of the San Andreas fault system and will form a critical framework for applying the knowledge gained in a deep San Andreas borehole to other segments of the fault and other tectonic environments.

California, Nevada↗
USGS2010

Scale-invariant stress orientations and seismicity rates near the San Andreas Fault

We analyzed measurements of the direction of maximum horizontal compressive stress as a function of depth in two scientific research wells near the San Andreas Fault in central and southern California. We found that the stress orientations exhibit scale-invariant fluctuations over intervals from tens of cm to several km. Similarity between the scaling of the stress orientation fluctuations and the scaling of earthquake frequency with fault size suggests that these fluctuations are controlled by stress perturbations caused by slip on faults of various sizes in the critically-stressed crust adjacent to the fault. The apparent difference in stress scaling parameters between the two studies wells seem to correspond to differences in the earthquake magnitude-frequency statistics for the creeping versus locked sections of the fault along which these two wells are located. This suggests that stress heterogeneity adjacent to active faults like the San Andreas may reflect variations in stresses and loading conditions along the fault.

California↗
USGS2010

The style of late Cenozoic deformation at the eastern front of the California Coast Ranges

The 1983 Coalinga earthquake occurred at the eastern boundary of the California Coast Ranges in response to northeast directed thrusting. Such movements over the past 2 Ma have produced Coalinga anticline by folding above the blind eastern tip of the Coalinga thrust zone. The 600-km length of the Coast Ranges boundary shares a common structural setting that involves westward upturn of Cenozoic and Cretaceous strata at the eastern front of the Coast Ranges and a major, southwest facing step in the basement surface beneath the western Great Valley. Like Coalinga anticline, Pliocene and Quaternary folding and faulting along the rest of the boundary also result from northeast–southwest compression acting nearly perpendicular to the strike of the San Andreas fault. We suggest that much of this deformation is related to active thrusts beneath the eastern Coast Ranges. The step in the basement surface beneath the Great Valley seems to have controlled the distribution of this deformation and the shape of the Coast Ranges boundary.

California↗
USGS2004

A mechanical model of the San Andreas fault and SAFOD Pilot Hole stress measurements

Stress measurements made in the SAFOD pilot hole provide an opportunity to study the relation between crustal stress outside the fault zone and the stress state within it using an integrated mechanical model of a transform fault loaded in transpression. The results of this modeling indicate that only a fault model in which the effective friction is very low (<0.1) through the seismogenic thickness of the crust is capable of matching stress measurements made in both the far field and in the SAFOD pilot hole. The stress rotation measured with depth in the SAFOD pilot hole (???28??) appears to be a typical feature of a weak fault embedded in a strong crust and a weak upper mantle with laterally variable heat flow, although our best model predicts less rotation (15??) than observed. Stress magnitudes predicted by our model within the fault zone indicate low shear stress on planes parallel to the fault but a very anomalous mean stress, approximately twice the lithostatic stress. Copyright 2004 by the American Geophysical Union.

Geophysical Research Letters↗
USGS2002

34 - State of stress in the Earth's lithosphere

The state of stress in the lithosphere is the result of the forces acting upon and within it. Knowledge of the magnitude and distribution of these forces can be combined with mechanical, thermal and rheological constraints to examine a broad range of lithospheric deformational processes. For example, such knowledge contributes to a better understanding of the processes that both drive and inhibit lithospheric plate motions as well as the forces responsible for the occurrence of crustal earthquakes − both along plate boundaries and in intraplate regions. Although the topic of this chapter is the state of stress in the Earth's lithosphere, the comments below come primarily from the perspective of the state of stress in the brittle upper crust. As defined by the depth of shallow earthquakes, the brittle crust extends to ˜15–20 km depth at most continental locations around the world. This perspective is adopted here because nearly all the data available on lithospheric stress come from the upper crust of continents. Furthermore, in the sections that follow, we argue that, to first order, the state of stress in the brittle crust results from relatively large-scale lithospheric processes so that knowledge of crustal stress can be used to constrain the forces involved in these processes.

International Geophysics↗
USGS1997

Analysis of borehole televiewer measurements in the Vorotilov drillhole, Russia - First results

In the Eurasian part of the World Stress Map almost the whole region east of the Tornquist-Teisseyre line is terra incognita. The closure of this information gap is of fundamental importance to the understanding of the geodynamics of the Eurasian continent. A detailed analysis of stress-induced wellbore breakouts has been performed over a 4.1-km-long depth interval in the Vorotilov drillhole (VGS). The borehole is located in the central part of the Russian platform, right in the center of the Vorotilov meteorite impact crater 60 km to the NNE of the city of Nizni Novgorod. An ultrasonic borehole televiewer (BHTV) was used to obtain high-resolution acoustical images from the borehole wall. With an interactive system for analyzing BHTV data the azimuth and shape of borehole breakouts occurring in the depth range of 1.3–4.8 km were analyzed. A statistical analysis of the resulting orientation profile of the breakout azimuths yields an overall direction of the maximum horizontal principal stress S H of N 137°E ± 15°. Variations of breakout orientation with depth ranging from a few degrees up to more than 90° are seen on various depth scales. The observed stress direction of N 137°E agrees very well with the average S H orientation of N 145°E in Central Europe. If this measurement is taken as representative for the Russian platform, the stress field in Russia is only slightly rotated in comparison to Central Europe. This can possibly be interpreted as indicative for the stress field to be governed by broad scale tectonic forces, such as a strong contribution from the forces exerted by the collision zone in the Alpine-Himalayan belt and by the Mid-Atlantic ridge.

Vorotilov drillhole↗
USGS1997

Relationships among in-situ stress, fractures and faults, and fluid flow: Monterey formation, Santa Maria basin, California

We used borehole televiewer (BHTV) data from four wells within the onshore and offshore Santa Maria basin, California, to investigate the relationships among fracture distribution, orientation, and variation with depth and in-situ stress. Our analysis of stress-induced well-bore breakouts shows a uniform northeast maximum horizontal stress (S H max ) orientation in each well. This direction is consistent with the S H max direction determined from well-bore breakouts in other wells in this region, the northwest trend of active fold axes, and kinematic inversion of nearby earthquake focal plane mechanisms.

California↗
USGS1996

The Loma Prieta, California, Earthquake of October 17, 1989: Main shock characteristics

The October 17, 1989, Loma Prieta, Calif., earthquake (0004:15.2 G.m.t. October 18; lat 37.036º N., long 121.883º W.; 19-km depth) had a local magnitude (M L ) of about 6.7, a surface-wave magnitude (M S ) of 7.1, a seismic moment of 2.2x10 19 N-m to 3.5x10 19 N-m, a source duration of 6 to 15 s, and an average stress drop of at least 50 bars. Slip occurred on a dipping fault surface about 35 km long and was largely confined to a depth of about 7 to 20 km. The slip vector had a large vertical component, and slip was distributed in two main regions situated northwest and southeast of the hypocenter. This slip distribution caused about half of the earthquake's energy to be focused toward the urbanized San Francisco Bay region, while the other half was focused toward the southeast. Had the rupture initiated at the southeast end of the aftershock zone, shaking in the bay region would have been both longer and stronger. These source parameters suggest that the earthquake was not a typical shallow San Andreas-type event but a deeper event on a different fault with a recurrence interval of many hundreds of years. Therefore, the potential for a damaging shallow event on the San Andreas fault in the Santa Cruz Mountains may still exist.

California↗
USGS1993

Deep hydraulic fracturing stress measurements in the KTB (Germany) and Cajon Pass (USA) Scientific Drilling Projects: A summary

The determination of in situ stresses along deep vertical profiles was declared a key issue for two scientific deep drilling projects: the German Continental Deep Drilling Project (KTB) situated in northeast Bavaria in an area of complex variscian thrust tectonics and the CAJON PASS Project, located only about 4 km from the San Andreas Fault Zone In southern California. In the KTB project 7 successful hydrofrac stress measurements could be completed in a 4 km deep pilot hole between 0.8 to 3.0 km. At the Cajon Pass site a series of 23 hydrofrac stress measurements was performed in 2 wells between 0.9 to 3.5 km.

Bavaria, California↗
USGS1992

Rapid intraplate strain accumulation in the New Madrid seismic zone

Remeasurement of a triangulation network in the southern part of the New Madrid seismic zone with the Global Positioning System has revealed rapid crustal strain accumulation since the 1950s. This area experienced three large (moment magnitudes >8) earthquakes in 1811 to 1812. The orientation and sense of shear is consistent with right-lateral strike slip motion along a northeast-trending fault zone (as indicated by current seismicity). Detection of crustal strain accumulation may be a useful discriminant for identifying areas where potentially damaging intraplate earthquakes may occur despite the absence of large earthquakes during historic time.

New Madrid seismic zone↗