The seismotectonic fabric of central California

Hill, David P.; Eaton, Jerry P.; Ellsworth, William L.; Cockerham, Robert S.; Lester, F.W.; Corbett, Edward J.

doi:10.1130/dnag-csms-neo.107

Cited by 12 publications

(5 citation statements)

References 66 publications

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“…Miller and Furlong [1988] Figures 8 and 9). Eastward deepening of the seismogenic zone from 12 to 18 km is similarly associated with the Hayward-Calaveras-Green Valley fault zones in the San Francisco Bay area [Ellsworth et al, 1982;Hill et al, 1990Hill et al, , 1991]. This regional deepening of seismicity to the east is consistent with an eastward decline in heat flow [Lachenbruch and Sass, 1973Williams and Lachenbruch, 1991].…”

Section: San Andreas Fault Systemmentioning

confidence: 92%

Seismotectonics of the San Andreas Fault System between Point Arena and Cape Mendocino in northern California: Implications for the development and evolution of a young transform

Castillo¹,

Ellsworth²

1993

J. Geophys. Res.

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The northernmost and relatively youthful segment of the San Andreas fault system is situated within a 100+ km wide zone of northwest trending strike-slip faults that includes, from west to east, the San Andreas, Maacama, and Bartlett Springs faults. Although the San Andreas fault is the principal strike-slip fault in this system, it has been virtually aseismic since the 1906 earthquake. Moderate levels of seismicity locate to the east along the Maacama fault and, to a lesser extent, the Bartlett Springs fault at focal depths typical of other strike-slip faults within the San Andreas fault system in central California. North of the San Andreas fault system, within the Cape Mendocino area, earthquakes occur at depths of up to 40 km and primarily reflect internal deformation of the subducting Garda slab, and slip along the Mendocino Fracture Zone. Seismicity along the Maacama and Bartlett Springs faults is dominated by right-lateral to oblique-reverse slip along fault planes that dip 500-75 ø to the northeast. The northern extent of seismicity along these faults terminates near the surface projection of the southern edge of the Garda slab. The onset of seismicity along these faults may be related to the abrupt change in the elastic thickness of the North American plate as it enters the asthenaspheric window. The Maacama and Bartlett Springs faults are strike-parallel with active reverse faults within the forearc region of the Cascadia subductian zone. This preexisting structural fabric of northwest trending reverse faults in the forearc area appears to have strongly influenced the initial slip and complexity of these faults. Continuation of the moderately dipping Maacama fault to the southeast along the steeply dipping Healdsburg and Rodgers Creek fault zones and the near-vertical Hayward and Calaveras fault zones in the San Francisco Bay area suggests that these faults evolve toward a more vertical dip to minimize the shear stresses that tend to resist plate motion.

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Section: San Andreas Fault Systemmentioning

confidence: 92%

Seismotectonics of the San Andreas Fault System between Point Arena and Cape Mendocino in northern California: Implications for the development and evolution of a young transform

Castillo¹,

Ellsworth²

1993

J. Geophys. Res.

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“…Boxed areas are cross sections shown in Figures 3 and 5. (Sources of data for cross section are as follows: Moho depth, reflectivity, and relief, Klemperer et al [1986]; velocity structure, McCarthy and Thompson [1988]; depth of seismicity/brittle‐ductile transition, Vetter et al [1983], Hill et al [1991], Northern California Earthquake Data Center (NCEDC), and Council of the National Seismic System (CNSS) for the years 1950–1996 (between latitudes 38°30′ N and 39°15′ N); heat flow data, Blackwell et al[1991]; depth of sedimentary basins, calculated from gravity data: depth = g max /2πGρT [e.g., Blakely , 1995]; basaltic underplating, e.g., Jarchow and Thompson [1993]. [The full size Figure 2 is available at http://www.agu.org/journals/tc.…”

Section: Introductionmentioning

confidence: 99%

Two‐phase westward encroachment of Basin and Range extension into the northern Sierra Nevada

et al. 2002

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[1] Structural, geophysical, and thermochronological data from the transition zone between the Sierra Nevada and the Basin and Range province at latitude $39°N suggest $100 km westward encroachment of Basin and Range extensional deformation since the middle Miocene. Extension, accommodated primarily by east dipping normal faults that bound west tilted, range-forming fault blocks, varies in magnitude from <2% in the interior of the Sierra Nevada crustal block to >150% in the Wassuk and Singatse Ranges to the east. Geological and apatite fission track data from exhumed upper crustal sections in the Wassuk and Singatse Ranges point to rapid footwall cooling related to large magnitude extension starting at $14 -15 Ma. Farther to the west, geological and thermochronological data indicate a younger period of extension in the previously unextended Pine Nut Mountains, the Carson Range, and the Tahoe-Truckee depression initiated between 10 Ma and 3 Ma, and incipient post-0.5 Ma faulting to the west of the Tahoe-Truckee area. These data imply the presence of an extensional breakaway zone between the Singatse Range and the Pine Nut Mountains at $14 -15 Ma, forming the boundary between the Sierra Nevada and Basin and Range at that time. In addition, fission track data imply a Miocene preextensional geothermal gradient of 27 ± 5°C km À1 in the central Wassuk Range and 20 ± 5°C km À1 in the Singatse Range, much higher than the estimated early Tertiary gradient of 10 ± 5°C km À1 for the Sierra Nevada batholith. This might point to a significant increase in geothermal gradients coupled with a likely decrease in crustal strength enabling the initiation of extensional faulting. Apatite fission track, geophysical, and geological constraints across the Sierra Nevada-Basin and Range transition zone indicate a twostage, coupled structural and thermal westward encroachment of the Basin and Range province into the Sierra Nevada since the middle Miocene.

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“…The seismicity data used in this work are from the California Seismic Network (Calnet) catalog [Hill et al, 1991]. We use events having horizontal errors < i km, rms misfits < 0.15 s, at least five phase arrivals picked, and the largest gap in azimuths of stations about the epicenter < 91 ø.…”

Section: Datamentioning

confidence: 99%

Rate and state of background stress estimated from the aftershocks of the 1989 Loma Prieta, California, earthquake

Gross¹,

Bürgmann²

1998

J. Geophys. Res.

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Abstract. Estimates of the tectonic stress state including loading rate and magnitude of background stress are derived from the spatial and temporal distribution of Loma Prieta aftershocks. This technique was previously applied to the Landers aftershock sequence [Gross and Kisslinger, 1997] and is based upon the seismicity model of Dieterich [1994]. Dieterich's theory suggests that background seismicity should be proportional to stress rate and the number of aftershocks in an area should be proportional to the stress step experienced in that area. We used two independently derived source models to compute the stress step from the mainshock and to determine how effective that stress step was in triggering aftershocks. A background stress state is then chosen which makes the stress steps at the aftershock locations most distinct from the stress steps at hypocenters of background seismicity. The best fitting background stress state has its greatest compressive stress plunging • 17 ø to N13øE, and an intermediate stress very close in magnitude to the least principal stress. The small shear stresses at depth and low coefficient of friction suggest that high-pressure pore fluids may be present inside active faults. The estimated stress rate of •-70 Paid (0.25 bar/yr) is comparable to the stress rate found for the southern San Andreas Fault system. We found a best fitting "effective" coe•cient of friction/• • 0.2 for the Loma Prieta area, significantly less than • • 0.6 estimated for Landers in previous work.Variations in aftershock decay rate within the Loma Prieta aftershock zone are correlated with static stresses caused by postseismic slip as modeled by •irgmann et al. [1997]. Some of the postseismic slip occurred on structures that did not slip during the mainshock, so the postseismic and coseismic stress step fields have different spatial distributions. The effectiveness of slowly accumulated postseismic static stresses in triggering aftershocks is especially interesting because dynamic stresses are insignificant in this case. IntroductionThe 1989 Mw = 7.0 Loma Prieta earthquake was a very educational event for the seismological community, illustrating the significance of seismic hazard from events that do not break the surface. Loma Prieta also raised some important questions relating to earthquake source mechanics because the aftershock focal mechanisms were so diverse that they suggested that slip on the mainshock had completely relieved homogeneous resolved shear stresses on the mainshock fault plane Copyright 1998 by the American Geophysical Union. Paper number 97JB03010.0148-227 / 98 / 97 JB-03010509.00 [Michael et al., 1990]. Effectively zero shear stresses following the mainshock were unexpected because they imply very low dynamic coefficients of friction, which had not been observed in the laboratory. In combination with the modest stress drop, the low residual stresses on the fault plane also suggest that either the static coefficient of friction was quite low or the effective normal stress was much les...

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The seismotectonic fabric of central California

Cited by 12 publications

References 66 publications

Seismotectonics of the San Andreas Fault System between Point Arena and Cape Mendocino in northern California: Implications for the development and evolution of a young transform

Seismotectonics of the San Andreas Fault System between Point Arena and Cape Mendocino in northern California: Implications for the development and evolution of a young transform

Two‐phase westward encroachment of Basin and Range extension into the northern Sierra Nevada

Rate and state of background stress estimated from the aftershocks of the 1989 Loma Prieta, California, earthquake

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