Crustal structure across the San Andreas Fault, southern California from teleseismic converted waves

Zhu, Lupei

doi:10.1016/s0012-821x(00)00101-1

Cited by 273 publications

(215 citation statements)

References 33 publications

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“…Such a narrow fault zone in the upper mantle in the presence of a low-viscosity lower crust would generate a broad deformation zone in the upper crust consisting of many parallel faults. Some support for the idea that the ECSZ may become narrower at depth is provided by a seismically observed offset in the Mohorovicic discontinuity (depth -30 km) beneath the ECSZ [Zhu, 2000].…”

Section: Discussionmentioning

confidence: 99%

Strain accumulation and rotation in the Eastern California Shear Zone

Savage¹,

Gan²,

Svarc³

2001

J. Geophys. Res.

162

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Abstract. Although the Eastern California Shear Zone (ECSZ) (strike -N25øW) does not quite coincide with a small circle drawn about the Pacific-North America pole of rotation, trilateration and GPS measurements demonstrate that the motion within the zone corresponds to right-lateral simple shear across a vertical plane (strike N33øW_+5 ø) roughly parallel to the tangent to that local small circle (strike -N40øW). If the simple shear is released by slip on faults subparallel to the shear zone, the accumulated rotation is also released, leaving no secular rotation. South of the Garlock fault the principal faults (e.g., Calico-Blackwater fault) strike -N40øW, close enough to the strike of the vertical plane across which maximum right-lateral shear accumulates to almost wholly accommodate that accumulation of both strain and rotation by right-lateral slip. North of the Garlock fault dip slip as well as strike slip on the principal faults (strike -N20øW) is required to accommodate the simple shear accumulation. In both cases the accumulated rotation is released with the shear strain. The Garlock fault, which transects the ECSZ, is not offset by northnorthwest striking faults nor, despite geological evidence for long-term left-lateral slip, does it appear at the present time to be accumulating left-lateral simple shear strain across the fault due to slip at depth. Rather the motion is explained by right-lateral simple shear across the orthogonal ECSZ. Left-lateral slip on the Garlock fault will release the shear strain accumulating there but would augment the accumulating rotation, resulting in a secular clockwise rotation rate -80 nrad yr -1 (4.6 ø Myr-1).

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Section: Discussionmentioning

confidence: 99%

Strain accumulation and rotation in the Eastern California Shear Zone

Savage¹,

Gan²,

Svarc³

2001

J. Geophys. Res.

162

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“…Prior studies of other continental strike-slip systems (Pili et al, 1997a,b) suggest that such large shear zone systems could possibly have mantle roots. Furthermore, Henstock et al (1997) and Zhu (2000) describe evidence for vertical offsets of the Moho under the San Andreas Fault, and Yan and Clayton (2007) found a notch structure on the Moho beneath the Eastern San Gabriel Mountains. Teyssier and Tikoff (1998), from seismic anisotropy and rheology, pictured a vertical lithospheric structure for the SAF, and Titus et al (2007) provided petrological evidence in xenoliths for the continuation of the SAF system into the upper mantle.…”

Section: Fluid Regime and Structure Of The San Andreas Faultmentioning

confidence: 96%

Isotopic evidence for the infiltration of mantle and metamorphic CO2–H2O fluids from below in faulted rocks from the San Andreas Fault system

et al. 2011

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To characterize the origin of the fluids involved in the San Andreas Fault (SAF) system, we carried out an isotope study of exhumed faulted rocks from deformation zones, vein fillings and their hosts and the fluid inclusions associated with these materials. Samples were collected from segments along the SAF system selected to provide a depth profile from upper to lower crust. In all, 75 samples from various structures and lithologies from 13 localities were analyzed for noble gas, carbon, and oxygen isotope compositions. Fluid inclusions exhibit helium isotope ratios ( 3 He/ 4 He) of 0.1-2.5 times the ratio in air, indicating that past fluids percolating through the SAF system contained mantle helium contributions of at least 35%, similar to what has been measured in present-day ground waters associated with the fault . Calcite is the predominant vein mineral and is a common accessory mineral in deformation zones. A systematic variation of C-and O-isotope compositions of carbonates from veins, deformation zones and their hosts suggests percolation by external fluids of similar compositions and origin with the amount of fluid infiltration increasing from host rocks to vein to deformation zones. The isotopic trend observed for carbonates in veins and deformation zones follows that shown by carbonates in host limestones, marbles, and other host rocks, increasing with increasing contribution of deep metamorphic crustal volatiles. At each crustal level, the composition of the infiltrating fluids is thus buffered by deeper metamorphic sources. A negative correlation between calcite δ 13 C and fluid inclusion 3 He/ 4 He is consistent with a mantle origin for a fraction of the infiltrating CO 2 . Noble gas and stable isotope systematics show consistent evidence for the involvement of mantle-derived fluids combined with infiltration of deep metamorphic H 2 O and CO 2 in faulting, supporting the involvement of deep fluids percolating through and perhaps weakening the fault zone. There is no clear evidence for a significant contribution from meteoric water, except for overprinting related to late weathering.

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“…We filtered our RFs between 0.033 and 0.25 Hz in order to detect conversions from the MTZ and converted the arrival times of each RF to depth using a model based upon IASP91 [Kennett and Engdahl, 1991] but adapted to include regional upper mantle P and S wave velocity anomalies [Montelli et al, 2006, hereafter M06]. The conversion points were migrated to their correct geometric positions [Zhu, 2000] and converted energy binned into voxels and smoothed (according to the size of the Fresnel zone and vertical resolution of the RFs) to produce final migrated images of the MTZ discontinuity depths (we follow a similar data reduction scheme to Hetényi et al [2009]). The potential vertical resolution of RFs at the considered frequencies and depths is ∼5 and ∼6 km at the '410' and '660', whilst the lateral resolution is estimated to be ∼125 and ∼160 km, respectively.…”

Section: Data and Processingmentioning

confidence: 99%

Mantle transition zone variations beneath the Ethiopian Rift and Afar: Chemical heterogeneity within a hot mantle?

Cornwell

Hetényi

Blanchard

2011

Geophys. Res. Lett.

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[1] The mantle transition zone (MTZ) structure beneath the Ethiopian Rift and Afar is mapped using receiver functions. The 410 discontinuity is flat and regionally depressed by 30-40 km, most likely due to a hot (≥+250°C) and slow (average dV S > 3 %) upper mantle. The 660 discontinuity is shown to have variations in depth (665-705 km) over short length scales (<200 km). This results in a MTZ with a 'normal' average thickness of 244 km, (i.e., within error of the observed global average). However, local thickness variations (<230 km to >260 km) indicate possible compositional/ chemical heterogeneities and elevated ambient temperatures near the base of the MTZ. These observations provide evidence for a link between the low velocity anomalies of the Ethiopian upper mantle and the African Superplume in the lower mantle.

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Crustal structure across the San Andreas Fault, southern California from teleseismic converted waves

Cited by 273 publications

References 33 publications

Strain accumulation and rotation in the Eastern California Shear Zone

Strain accumulation and rotation in the Eastern California Shear Zone

Isotopic evidence for the infiltration of mantle and metamorphic CO2–H2O fluids from below in faulted rocks from the San Andreas Fault system

Mantle transition zone variations beneath the Ethiopian Rift and Afar: Chemical heterogeneity within a hot mantle?

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