Intraslab Earthquakes: Dehydration of the Cascadia Slab

Preston, Leiph; Creager, K. C.; Crosson, Robert S.; Brocher, Thomas M.; Tréhu, Anne M.

doi:10.1126/science.1090751

Cited by 93 publications

(114 citation statements)

References 16 publications

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“…Since 1945, there have been several events with magnitudes >5.5, including the 6.8 Nisqually earthquake in 2001 that resulted in an estimated monetary loss of more than USD two billion (Kirby and Wang, 2002). Most of these events have epicenters located between 35 and 70 km depth, with some small events reaching depths up to 100 km (Preston et al, 2003). Additionally, the Puget lowland region of central and northern Washington, which is a focus of this study, experiences a much higher incidence of these earthquakes than neighboring regions to the north and south.…”

Section: The Cascadia Subduction Systemmentioning

confidence: 99%

“…Intraslab earthquakes have been linked with a process in which fluids released during the transformation of hydrated metabasalts to eclogite in the upper crust increases pore pressure, thereby reactivating pre-existing faults (Kirby et al, 1996, Preston et al, 2003. Slow slip and low frequency tremor, which have been tentatively linked with the periodicity of great megathrust earthquakes (Mazzotti and Adams, 2004), can be explained by episodic buildup and release of fluid pore pressure across plate boundaries down-dip of the locked zone .…”

Section: Introductionmentioning

confidence: 99%

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The CAFE Experiment : a joint seismic and MT investigation of the Cascadia Subduction System

McGary¹

2013

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In this thesis we present results from inversion of data using dense arrays of collocated seismic and magnetotelluric stations located in the Cascadia subduction zone region of central Washington. In the migrated seismic section, we clearly image the top of the slab and oceanic Moho, as well as a velocity increase corresponding to the eclogitization of the hydrated upper crust. A deeper velocity increase is interpreted as the eclogitization of metastable gabbros, assisted by fluids released from the dehydration of upper mantle chlorite. A low velocity feature interpreted as a fluid/melt phase is present above this transition. The serpentinized wedge and continental Moho are also imaged. The magnetotelluric image further constrains the fluid/melt features, showing a rising conductive feature that forms a column up to a conductor indicative of a magma chamber feeding Mt. Rainier. This feature also explains the disruption of the continental Moho found in the migrated image. Exploration of the assumption of smoothness implicit in the standard MT inversion provides tools that enable us to generate a more accurate MT model. This final MT model clearly demonstrates the link between slab derived fluids/melting and the Mt. Rainier magma chamber.

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Section: The Cascadia Subduction Systemmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The CAFE Experiment : a joint seismic and MT investigation of the Cascadia Subduction System

McGary¹

2013

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“…generally thought to arise from dehydration reactions [Kao et al, 2008;Preston et al, 2003]. Reflection banding is also present above the megathrust and is likely related to fluids given the high electrical conductivity associated with this zone [Nedimović et al, 2003].…”

Section: The Cascadia Subduction Marginmentioning

confidence: 99%

“…Audet et al, 2009;Bostock et al, 2002;Hacker et al, 2003;Kao et al, 2005;Preston et al, 2003;Rogers and Dragert, 2003;Walowski et al, 2015]. Prior studies within the interior of the JdF plate provide evidence for hydration of the upper crust associated with ridge flank hydrothermal circulation and spatially correlated with local zones of ridge propagation [McClymont and Clowes, 2005;Nedimović et al, 2009;Nedimović et al, 2008;Newman et al, 2011] but the full extent of when and how water is incorporated into the lithosphere during the evolution of the JdF plate, and how water is distributed at depth within the plate prior to subduction remains unknown.…”

Section: Introductionmentioning

confidence: 99%

Geophysical and geochemical constraints on the evolution of oceanic lithosphere from formation to subduction

Horning¹

2017

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This thesis investigates the evolution of the oceanic lithosphere in a broad sense from formation to subduction, in a focused case at the ridge, and in a focused case proximal to subduction. In general, alteration of the oceanic lithosphere begins at the ridge through focused and diffuse hydrothermal flow, continues off axis through low temperature circulation, and may occur approaching subduction zones as bending related faulting provides fluid pathways. In Chapter 2 I use a dataset of thousands of microearthquakes recorded at the Rainbow massif on the Mid-Atlantic Ridge to characterize the processes which are responsible for the long-term, high-temperature, hydrothermal discharge found hosted in this oceanic core complex. I find that the detachment fault responsible for the uplift of the massif is inactive and that the axial valleys show no evidence for faulting or active magma intrusion. I conclude that the continuous, low-magnitude seismicity located in diffuse pattern in a region with seismic velocities indicating ultramafic host rock suggests that serpentinization may play a role in microearthquake generation but the seismic network was not capable of providing robust focal mechanism solutions to constrain the source characteristics. In Chapter 3 I find that the Juan de Fuca plate, which represents the young/hot end-member of oceanic plates, is lightly hydrated at upper crustal levels except in regions affected by propagator wakes where hydration of lower crust and upper mantle is evident. I conclude that at the subduction zone the plate is nearly dry at upper mantle levels with the majority of water contained in the crust. Finally, in Chapter 4 I examine samples of cretaceous age serpentinite sampled just before subduction at the Puerto Rico Trench. I show that these upper mantle rocks were completely serpentinized under static conditions at the Mid-Atlantic Ridge. Further, they subsequently underwent 100 Ma of seafloor weathering wherein the alteration products of serpentinization themselves continue to be altered. I conclude that complete hydration of the upper mantle is not the end point in the evolution of oceanic lithosphere as it spreads from the axis to subduction. Chapter 1: IntroductionThe total water content of the oceanic lithosphere is the sum of the free water in pore spaces in the sedimentary cover and highly porous upper crust, chemically bound water in sediment clay minerals, chemically bound water in the upper and lower crust resulting from the precipitation of secondary hydrous alteration products, free water in fault zones, and bound water of hydrous minerals in the uppermost mantle resulting from serpentinization of peridotite. This thesis is focused on characterizing the location, extent, and timing of the processes that result in this alteration of the lithosphere.In Chapter 2 I focus on the alteration that occurs in the near axis region at an oceanic core complex located on the slow spreading Mid-Atlantic Ridge. At the Rainbow massif long-lived high-T hydrothermal venting h...

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“…[12] The three-dimensional (3-D) P wave velocity model for the YM region was developed with a nonlinear inversion procedure [Preston et al, 2003], an iterative technique that simultaneously solves for optimal earthquake locations and 3-D P wave velocity structure from P wave arrival times. The solution is regularized by seeking a smooth velocity structure.…”

Section: Data Method and Modelingmentioning

confidence: 99%

P wave velocity structure in the Yucca Mountain, Nevada, region

2007

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We have performed a crustal tomographic inversion using over 250,000 P arrival times from local earthquake sources and surface explosions in the Yucca Mountain, Nevada, region. Within the shallowest 2–3 km, topographic features tend to dominate the structure with high velocities imaged under Bare Mountain, the Funeral Mountains, and higher terrain to the east of Yucca Mountain and low velocities imaged under Crater Flat, Jackass Flat, the Amargosa Desert, and the caldera complexes. Imaged shallow velocities also show correlation with several known gravity and aeromagnetic anomalies. Below the basins (∼2–3 km depth), velocities vary between 5.5 and 6.5 km/s and lose many of the correlations seen in the shallowest layers; however, a few major structures, such as the Bare Mountain block, can be traced to at least 10 km depth. Additionally, we image structures that may be associated with the Wahmonie intrusion and pre‐Tertiary structural trends. Yucca Mountain itself is underlain by a high‐velocity upper crustal‐scale structure similar to other structures in the region such as Bare Mountain and may represent a Basin and Range style back‐tilted block, which may provide a structural explanation for Yucca Mountain's topographic expression. Additionally, the imaged, relatively low velocity basement under Crater Flat may provide a preferred conduit for magma intrusion into Crater Flat compared to Yucca Mountain, accounting for the lack of post‐Miocene volcanism observed at the mountain proper. We explore our tomographic results in the context of four major tectonic models that have been proposed for the Yucca Mountain region.

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Intraslab Earthquakes: Dehydration of the Cascadia Slab

Cited by 93 publications

References 16 publications

The CAFE Experiment : a joint seismic and MT investigation of the Cascadia Subduction System

The CAFE Experiment : a joint seismic and MT investigation of the Cascadia Subduction System

Geophysical and geochemical constraints on the evolution of oceanic lithosphere from formation to subduction

P wave velocity structure in the Yucca Mountain, Nevada, region

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