Migration of the Mendocino triple junction and ephemeral crustal deformation: Implications for California Coast range heat flow

Guzofski, Chris A.; Furlong, Kevin P.

doi:10.1029/2001gl013614

Cited by 26 publications

(45 citation statements)

References 15 publications

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“… Lachenbruch and Sass [1980] show that background heat flow throughout the Coast Ranges is higher than the surrounding areas and not uniform. This “Coast Ranges high” is much broader than the anomalies we predict for frictional heat in the brittle upper crust and has been attributed to deep viscous heating [e.g., Thatcher and England , 1998] or hot asthenospheric intrusion into a “slab window” as the Farallon plate disappears from beneath California as the Mendocino triple junction moves northward [e.g., Lachenbruch and Sass , 1980; ten Brink et al , 1999; Guzofski and Furlong , 2002]. The stalled Monterey microplate underlying portions of our study area may further modify the background heat flow [ ten Brink et al , 1999].…”

Section: Is the Creeping Section Strong?mentioning

confidence: 96%

“…Figure S1 illustrates a 2‐D distribution of background heat flow determined by merging two 1‐D models. In those models, heat flow declines about 1 mW m −2 for every 20 km traveled southeast along the Coast Ranges [after Guzofski and Furlong , 2002], and heat flow drops by 30 mW m −2 over a ∼100‐km‐wide transition across the eastern edge of the Coast Ranges [ Lachenbruch and Sass , 1973; Williams et al , 2004]. For the most part, models constrain the along‐strike variation in the North American plate better than the east‐west variation.…”

Section: Is the Creeping Section Strong?mentioning

confidence: 99%

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Frictional strength heterogeneity and surface heat flow: Implications for the strength of the creeping San Andreas fault

2006

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[1] Heat flow measurements along much of the San Andreas fault (SAF) constrain the apparent coefficient of friction (m app ) of the fault to <0.2, much lower than laboratoryderived friction values for most geologic materials. However, heat flow data are sparse near the creeping section of the SAF, a frictional ''asperity'' where the fault slips almost exclusively by aseismic creep. We test the hypothesis that the creeping section has a substantially higher or lower m app than adjacent sections of the SAF. We use numerical models to explore the effects of faults with spatially and temporally heterogeneous frictional strength on the spatial distribution of surface heat flow. Heat flow from finite length asperities is uniformly lower than predicted by assuming an infinitely long fault. Over geologic time, lateral offset from strike-slip faulting produces heat flow patterns that are asymmetric across the fault and along strike. We explore a range of asperity sizes, slip rates, and displacement histories for comparing predicted spatial patterns of heat flow with existing measurements. Models with m app $ 0.1 fit the data best. For most scenarios, heat flow anomalies from a frictional asperity with m app > 0.2 should be detectable even with the sparse existing observations, implying that m app for the creeping section is as low as the surrounding SAF. Because the creeping section does not slip in large earthquakes, the mechanism controlling its weakness is not related to dynamic processes resulting from high slip rate earthquake ruptures.

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Section: Is the Creeping Section Strong?mentioning

confidence: 96%

Section: Is the Creeping Section Strong?mentioning

confidence: 99%

Frictional strength heterogeneity and surface heat flow: Implications for the strength of the creeping San Andreas fault

2006

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“…The MTJ and the subducting slab have migrated northward over time, and in its wake, subduction analogous to that occurring in present‐day Cascadia has been replaced by the strike‐slip tectonics of the SAF system [ Atwater and Stock , 1998]. As the subducting slab is replaced with upwelled asthenosphere (or remaining slab stalls beneath the overlying crust and thermally reequilibrates), serpentinized upper mantle, believed to remain beneath the North American crust, is heated (Figure 4b) [ ten Brink et al , 1999; Guzofski and Furlong , 2002; Kirby et al , 2002; Brocher et al , 2003; Erkan and Blackwell , 2008]. Serpentinite minerals are unique, and relevant to this study, in that they contain up to 10–13 wt% water in their mineral structure [ Iwamori , 1998].…”

Section: Introductionmentioning

confidence: 99%

Potential role of mantle‐derived fluids in weakening the San Andreas Fault

Fulton¹,

Saffer²

2009

J. Geophys. Res.

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[1] On the basis of both geomechanical and thermal data, the San Andreas Fault (SAF) has been interpreted to act as a weak plane within much stronger crust, allowing it to slip at very low shear stresses. One explanation for this weakness is that large fluid overpressures exist locally within the fault zone. However, mechanisms for generating, maintaining, and localizing pressures within the fault are poorly quantified. Here we evaluate whether realistic sources of mantle-derived fluids, proposed on the basis of high mantle helium signatures near the SAF, can generate localized fluid pressures within the fault zone in a manner consistent with a wide range of observations along the fault and in the San Andreas Fault Observatory at Depth borehole. We first calculate a reasonable estimate of the magnitude and location of a mantle-derived flux of water into the crust. This fluid flux results from dehydration of a serpentinized mantle wedge following the northward migration of the Mendocino Triple Junction and the transition from subduction to strike-slip tectonics. We then evaluate the potential effect of this water on fluid pressures within the crust using 2-D cross-sectional models of coupled fluid flow and heat transport. We show that in models with realistic permeability anisotropy, controlled by NE dipping faults and fractures within the country rock, large localized fluid pressures can be focused within a SAF acting as a hydrologic barrier. Our results illustrate a simple and potentially plausible means of weakening the SAF in a manner generally consistent with available hydrologic, thermal, and mechanical constraints.

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“…It is important to note that the cause of this high regional heat flow is not well understood. High heat flow throughout the California Coast Ranges has been interpreted as a transient thermal response to the migration of the Mendocino Triple Junction and associated slab window [Lachenbruch and Sass, 1980;Guzofski and Furlong, 2002]. Alternatively, Lachenbruch and Sass [1980] and Scholz [2000] note the possibility that the regionally high heat flow could reflect lower basal heat flux, combined with broadly redistributed frictionally generated heat from a strong SAF.…”

Section: Implications and Additional Considerationsmentioning

confidence: 99%

Topographically driven groundwater flow and the San Andreas heat flow paradox revisited

2003

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[1] Evidence for a weak San Andreas Fault includes (1) borehole heat flow measurements that show no evidence for a frictionally generated heat flow anomaly and (2) the inferred orientation of s 1 nearly perpendicular to the fault trace. Interpretations of the stress orientation data remain controversial, at least in close proximity to the fault, leading some researchers to hypothesize that the San Andreas Fault is, in fact, strong and that its thermal signature may be removed or redistributed by topographically driven groundwater flow in areas of rugged topography, such as typify the San Andreas Fault system. To evaluate this scenario, we use a steady state, two-dimensional model of coupled heat and fluid flow within cross sections oriented perpendicular to the fault and to the primary regional topography. Our results show that existing heat flow data near Parkfield, California, do not readily discriminate between the expected thermal signature of a strong fault and that of a weak fault. In contrast, for a wide range of groundwater flow scenarios in the Mojave Desert, models that include frictional heat generation along a strong fault are inconsistent with existing heat flow data, suggesting that the San Andreas Fault at this location is indeed weak. In both areas, comparison of modeling results and heat flow data suggest that advective redistribution of heat is minimal. The robust results for the Mojave region demonstrate that topographically driven groundwater flow, at least in two dimensions, is inadequate to obscure the frictionally generated heat flow anomaly from a strong fault. However, our results do not preclude the possibility of transient advective heat transport associated with earthquakes.

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Migration of the Mendocino triple junction and ephemeral crustal deformation: Implications for California Coast range heat flow

Cited by 26 publications

References 15 publications

Frictional strength heterogeneity and surface heat flow: Implications for the strength of the creeping San Andreas fault

Frictional strength heterogeneity and surface heat flow: Implications for the strength of the creeping San Andreas fault

Potential role of mantle‐derived fluids in weakening the San Andreas Fault

Topographically driven groundwater flow and the San Andreas heat flow paradox revisited

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