ISSN:0148-0227    

DOI:10.1029/JB088iB01p00513

年代:1983

数据来源: WILEY

摘要:

The deformation of the earth's surface immediately following an earthquake is well modeled by a dislocation in an elastic half space. Some time after the event, however, the elastic stresses begin to relax due to flow in the more fluid regions of the upper mantle (the asthenosphere). This relaxation causes further slow displacements observable at the earth's surface. This paper examines the pattern and timing of these postseismic motions for a vertical dip slip fault and a 30° dip thrust fault. A variety of rheological models are studied. These models encompass variations in asthenosphere thickness, mesosphere viscosity, fault depth, and, most important, power law flow. Both Newtonian (n= 1) and non‐Newtonian (n= 3) Maxwell rheologies are considered for the asthenosphere and mesosphere. The results for a vertical dip slip fault show that a peripheral upwarp develops within a distance of a few lithosphere thicknesses from the rupture zone on the downthrown side of the fault (a comparable downwarp develops on the upthrown side). These peripheral warps grow to a maximum height of about 5% of the total fault slip some time after the earthquake event and then collapse at much greater times. The vertical motions for a 30° dip thrust fault show that after the earthquake a general uplift occurs in the region near the rupture zone. Horizontal displacements propagate asymmetrically away from the rupture zone, the largest displacements occurring in the overthrust plate. The principal result of the comparison ofn= 1 andn= 3 rheological laws is that the basic pattern of uplifts and horizontal motions is very similar: the major difference is the time dependence of the development of the pattern. In spite of the complex geometrical structure of the subduction zone the displacementsui(1)(t) for Newtonian rheology are nearly the same asui(3)(t′) for the non‐Newtonian rheology ift′ ∼t3. Thus although the qualitative pattern of the displacements is not diagnostic of power law flow, the great difference in time dependence allows a clear discrimination of the tw

ISSN:0148-0227    

DOI:10.1029/JB088iB01p00515

年代:1983

数据来源: WILEY

摘要:

A contour map of crustalQ0values for the entire United States is presented based on a scattering model to explain the coda waves of local and near regional earthquakes. These codaQ0values are in good agreement withQofLgwaves. Data are obtained from over 250 local earthquakes, with most magnitudes between 3.0 and 5.0, recorded by 25 WWSSN and 27 LRSM stations throughout the continental United States. These two sets of data provide a range of frequencies from 0.5 to 3.5 Hz. A frequency dependence ofQis observed in the range of frequencies considered. A power law dependence of the formQ=Q0(f/f0)ηis assumed. The value of frequency dependence η, is found to be maximum in the tectonically active western United States and least in the stable regions of the central and south central United States. The lowestQ0values are obtained in the western United States, with values ranging from 140 to 200 in the Coastal Plains. Average crustalQ0values for the Basin and Range province vary from 200 to 300, increasing gradually to 400 in the Colorado Plateau region.Q0values in the Columbia Plateau vary from 200 to 400.Q0values increase very rapidly along the central and southern Rocky Mountains from 400 to 800. East of the Rocky MountainsQ0values increase gradually in the Interior Plains to a maximum value of around 1300 in the Mississippi Embayment region. Farther eastQ0values decrease gradually to an almost constant value of 1000 along the Appalachian Mountains. Coastal regions of eastern and northeastern United States have a crustalQ0value between 900 to 700. Regions of north central and Gulf Coastal Plains show lowQ0values, ranging from 600 to 400 and less. The source factorB(fp), a measure of the intensity of scattering, was obtained for several different regions of the continental United States. Regions of highQ0values exhibit low intensity of scatterin

ISSN:0148-0227    

DOI:10.1029/JB088iB01p00527

年代:1983

数据来源: WILEY

摘要:

Measurements of four of the five elastic stiffnesses of marine calcareous rocks and estimates of the fifth,c13, allow more detailed discussion of elastic wave propagation in these rocks than previously possible. The constantc13, which is seldom measured and was not measured in the rocks of this study, was derived by equating the Gassmann and Hashin‐Shtrikman estimates of the bulk moduli of chalk and limestone and then solving for the single unknownc13. For chalk, the measured constants, in N/m2×1010, arec11= 1.01,c33= 0.94,c44= 0.18, andc66= 0.21. For limestone, the measured constants, also in N/m2×1010, arec11= 2.41,c33= 2.09,c44= 0.47, andc66= 0.60. Three physically possible values ofc13were computed for chalk (0.48, 0.52, and 0.63 N/m2×1010) and for limestone (0.73, 1.05, and 1.24N /m2×1010). Heretofore, the only statements which could be made aboutc13in these rocks are |c13|<0.87×1010N/m2(chalk), and |c13|<1.94×1010N/m2(limestone). The calculations require the assumption that anisotropy in these rocks is caused by mineral alignment and the simplification of monomineralogy (calcite). On the basis of these measurements and estimates, the effect of elastic anisotropy on seismic reflection determinations of vertical compressional wave speed in calcareous rocks below the earth's surface is small ( ±6%), whereas similar determinations of vertically polarized shear wave speeds may be unreliable. Relationships are provided to convert seismic refraction measurements of horizontal compressional wave velocity to vertical velocity. These relationships are independent of the estimated valu

ISSN:0148-0227    

DOI:10.1029/JB088iB01p00539

年代:1983

数据来源: WILEY

摘要:

The measured attenuation (Q−1) of a rock is a function of a number of parameters, one of those being the applied strain amplitude. It is important to understand the effect that strain amplitude has onQ−1for several reasons: different measurement techniques use differing strain amplitudes and may measure a dissimilarQ−1, near source (large strain) wave propagation may behave highly non‐linearly, and the strain amplitude dependence can provide insight into the attenuation mechanism. A physical model based on the contact friction between crack surfaces in the rock has been developed to describe rock deformation and dissipation under large applied strain. The three‐dimensional crack surfaces are characterized by a statistical distribution of asperity heights. The sliding contact of these spherically‐tipped asperities dissipates frictional energy. Hertzian theory is applied to the average asperity contact and predicts that the large strain attenuation is given byQ−1=kζε/P4/3, wherekis a constant consisting of the matrix elastic parameters, ζ is the crack density, ε is the strain amplitude, andPis the confining pressure. The total attenuation measured appears to be the sum of this strain dependent term and a strain independent term. The results of ultrasonic pulse transmission experiments are compared with the model's prediction. BothPandSwaves with strain amplitudes from 10−8to 10−5were employed. Frequencies from 0.4 to 1.5 MHz were used in conjunction with rock confining pressures of 2 to 580 bars on dry Berea sandstone and lucite samples. The spectral ratio method and rise time technique were applied to deduce theQ−1values. The observed data and other observations from the literature compare well with the model's prediction for the dependence ofQ−1on large strain amplitude, cr

ISSN:0148-0227    

DOI:10.1029/JB088iB01p00546

年代:1983

数据来源: WILEY

摘要:

Fractures within granodiorite of the central Sierra Nevada, California, were studied to elucidate the mechanics of faulting in crystalline rocks, with emphasis on the nucleation of new fault surfaces and their subsequent propagation and growth. Within the study area the fractures form a single, subparallel array which strikes N50°–70°E and dips steeply to the south. Some of these fractures are identified as joints because displacements across the fracture surfaces exhibit dilation but no slip. The joints are filled with undeformed minerals, including epidote and chlorite. Other fractures are identified as small faults because they display left‐lateral strike slip separations of up to 2 m. Slickensides, developed on fault surfaces, plunge 0°–20° to the east. The faults occur parallel to, and in the same outcrop with, the joints. The faults are filled with epidote, chlorite, and quartz, which exhibit textural evidence of shear deformation. These observations indicate that the strike slip faults nucleated on earlier formed, mineral‐filled joints. Secondary, dilational fractures propagated from near the ends of some small faults contemporaneously with the left‐lateral slip on the faults. These fractures trend 25°±10° from the fault planes, parallel to the direction of inferred local maximum compressive stress. The faults did not propagate into intact rock in their own planes as shear fractures. Rather, adjacent faults were linked together by secondary, dilational fractures. Extensive secondary fracturing between faults produced larger fault zones that accommodate 10–100 m of left‐lateral slip. As deformation progressed, faulting evolved from relatively short, closely spaced faults to longer, more widel

ISSN:0148-0227    

DOI:10.1029/JB088iB01p00555

年代:1983

数据来源: WILEY

摘要:

The Ventura basin is an east‐north‐east trending trough in the California Transverse Ranges which records major Quaternary detachment faulting at three levels. The earliest thrusting occurred along weak siltstone interbeds in a sequence dominated by competent basin‐plain turbidite sandstone. Because sedimentation continued during thrusting, the age, rate, and direction of thrusting can be worked out. Faulting began 1.3 m.y. ago and ceased 0.65 m.y. ago, with a maximum slip rate of 2.8 mm/yr to the southeast. The fault set moved up a 45° ramp and ended as a blind thrust. The ramp had topographic expression on the seafloor, diverting turbidites around the ramp and preserving ash beds along with other hemipelagic sediments on its crest. Following the end of deposition 0.2 m.y. ago, the competent basin‐plain turbidites underwent flexural slip folding over an incompetent Miocene sequence dominated by shale; underlying competent Paleogene strata were not folded. The south flank of the Ventura Avenue anticline tilted at 3.4 μrad/yr, the anticlinal crest rose at a rate of 15–16 mm/yr decelerating to 4.3–5.2 mm/yr, and the anticline and an adjacent syncline shortened at a rate of 20 mm/yr. The high rate of folding in the Ventura Avenue oil field resulted in overpressured sandstone reservoirs and oil‐water interfaces which have not had time to reach gravity equilibrium. The Red Mountain, San Cayetano, and Santa Susana faults mark the surface expression of a seismically active midcrustal detachment which produced convergence across the Ventura basin at rates as high as 23 mm/yr. Total convergence across the eastern San Cayetano fault near Fillmore is 11,600±2000 m in the la

ISSN:0148-0227    

DOI:10.1029/JB088iB01p00569

年代:1983

数据来源: WILEY

摘要:

A study is made of the critical phenomena associated with the onset of conductivity and the onset of failure in a rock with a random distribution of microcracks using a renormalization group theory approach. The interaction between different length scales is an important element in the theory, which is a departure from the results of equivalent media theory. The crack parameter that determines if the rock can conduct or is to fail is the crack count per unit area times the square of the crack length. The parameter space is divided up into regions or phases. These phases are those of no conduction and no failure, conduction and no failure, and conduction and failure. The predictions of the model agree well with SEM data on the microcrack populations of stressed and unstressed rock samples. The crack densities seen in unstressed Westerly granite fall in the range that predicts conduction but no failure, but only a 50% increase in density is needed to reach the failure criteria. A sample stressed to 65% of the failure stress has greatly increased conduction connectivity but seems no closer to failure. The sample stressed to failure shows an appropriate crack density increase.

ISSN:0148-0227    

DOI:10.1029/JB088iB01p00585

年代:1983

数据来源: WILEY

摘要:

Numerical solutions of the equations of fluid flow and heat transport are used to quantify the effects of groundwater flow on the subsurface thermal regime. Simulations are carried out for a vertical section through a basin with a distance of 40 km separating the regional topographic high and low. Emphasis is placed on understanding the conditions under which advective effects significantly perturb the thermal field. The transition from conduction‐dominated to advection‐dominated thermal regimes is sharp and depends primarily on the topographic configuration of the water table, the magnitude and spatial distribution of permeability, hydraulic anisotropy, and the depth of active flow. Deviations of surface heat flow from the background heat flux are a measurable effect of groundwater flow and depend on the same factors. Our results show that from 0% to almost 100% of the section may have surface heat flow significantly different from background heat flow, depending upon the nature of the hydrogeologic environment. A limited spatial variability in a distributed set of heat flow measurements and/or linear temperature‐depth profiles does not ensure that surface heat flow measurements are not disturbed. The results of our simulations suggest that knowledge of the complete environment of a site, including the water table configuration and subsurface flow system, combined with more closely spaced heat flow measurements may be necessary to unravel the true background heat flux in active flow re

ISSN:0148-0227    

DOI:10.1029/JB088iB01p00593

年代:1983

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1029/JB088iB01p00609

年代:1983

数据来源: WILEY