Are deep focus earthquakes caused by a martensitic transformation?

Lomnitz-Adler, J.

doi:10.4294/jpe1952.38.83

Cited by 11 publications

(3 citation statements)

References 34 publications

(23 reference statements)

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“…One solution to the enigma of deep earthquakes [Frohlich, 1989;Lomnitz-Adler, 1990] invokes effects related to phase changes in metastable olivine held too cool in the interior of a subducted lithospheric slab to transform to wadsleyite [Kirby et al, 1996;Bina, 1996]. The simplest model envisages a wedge of metastable olivine bounded by an isotherm extending downward in the slab's core from reaction (1)'s equilibrium position.…”

Section: Deep Earthquake Modelsmentioning

confidence: 99%

Topography of the transition zone seismic discontinuities

Helffrich¹

2000

Reviews of Geophysics

257

192

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Abstract.Phase transformations in mantle mineralogies probably cause the transition zone seismic discontinuities, nominally at 410, 520, and 660 km depth. , 1923]. This paper focuses on the mantle discontinuities in the transition zone, the region between about 400 and 800 km depth. Whereas in seismology's nascency new discontinuity discoveries progressively refined our basic knowledge of Earth structure, in its maturity the discontinuities themselves become investigative tools rather than investigative targets. The goal of this review is to show how changes in discontinuity depth have been and can be used to investigate the mantle's properties. The argument develops along two lines. The first establishes what the major discontinuities at 410, 520, and 660 km depth are. Significantly, the topography on the discontinuities gives strong evidence to discriminate among different ideas about how they arise. The second strand describes the sort of scientific craftsmanship that can be achieved using the spatial variation of discontinuity depths as a tool, a tool that turns out to be surprisingly versatile, under continual refinement, and increasingly common in a research seismologist's tool kit. Detecting DiscontinuitiesSeismic discontinuities are detected by the additional arrivals they cause in the seismic wave field by reflection and refraction of the direct wave at the discontinuity. Reflection typically leads to an earlier arrival than would be expected in a uniform medium. Its timing relative to the direct arrival yields the discontinuity's depth. A refraction usually leads to more than one arrival, where only one would be expected in a uniform medium. In this case, one deduces the discontinuity depth from the distance from the seismic source where the multiple arrivals appear. The Earth's major discontinuities were initially discovered this way, and others continue to be discovered like this [Oldham, 1906;Lehmann, 1936;Song and Helmberger, 1998].There are quite diverse methods for measuring discontinuity depths, probably best described through sketches (Figure 2) (see Shearer [1991] for more exotic ones). One way to characterize the methods is by the position where the seismic wave interacts with the discontinuity: near the source, near the receiver, or elsewhere. Near-source studies provide the best spatial resolution because there is little opportunity for the seismic wave field to spread out before interacting with the discontinuity (its Fresnel zone width is small). Spatial resolution for near-receiver studies is worse since the interaction is at least 410 km from the receiver. Interac-

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Section: Deep Earthquake Modelsmentioning

confidence: 99%

Topography of the transition zone seismic discontinuities

Helffrich¹

2000

Reviews of Geophysics

257

192

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“…The three South American events all have very small seismic efficiencies and average rupture velocities, indicating that the sources were highly dissipative, while the events from the colder slabs have greater seismic efficiencies and rupture velocities. This temperature dependency suggests that plastic instability or shear-induced melting [Griggs and Baker, 1969;McKenzie and Brune, 1972;Ogawa, 1987;Hobbs and Ord, 1988;Lomnitz-Adler, 1990;Spray, 1993;Kikuchi and Kanamori, 1994] caused by phase-transformation-induced grain size reduction [Riedel and Karato, 1997] is a viable mechanism of deep earthquake rupture. Kanamori et al [ 1998] and McGuire et al [ 1997] suggested that the mechanisms of rupture initiation and propagation might differ, possibly initiating as transformational faulting but propagating farther via shear-induced melting or plastic instability.…”

Section: Comparison With Other Large Deep Eventsmentioning

confidence: 99%

Body wave inversion of the 1970 and 1963 South American large deep‐focus earthquakes

Estabrook¹

1999

J. Geophys. Res.

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Abstract. A comprehensive set of teleseismic waveforms from two South American deep-focus earthquakes of the predigital era, the 1970 Colombia (Mw-8.1) and 1963 Peru-Bolivia (Mw = 7.7) events, are inverted for source mechanism, seismic moment, rupture history, and cemroid depth. The P and SH wave inversion of the Colombia event confirms previous work, indicating that rupture occurred on a plane that dips steeply west. Rupture direction paralleled the trend of the Wadati-Benioff zone. We decompose the source into subevents, based on a source time function which shows two major moment release pulses separated by ~20 s. The first subevent is located near the initiation point at a depth of ~630 kin. The main moment release was located ~70 km to the southeast and ~20 km shallower. Rupture subsequently propagated farther southeast.

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“…Several large deep‐focus earthquakes in 1994 and 1996 have come as a test of models for the occurrence of deep earthquakes. These models include transformational faulting of olivine to spinel [ Green and Burnley , 1989; Kirby et al , 1992; Green and Houston , 1995; Green and Zhou , 1996]; clinoenstatite to ilmenite [ Akaogi et al , 1987; Hogrefe et al , 1994; Kirby et al , 1996]; serpentinite dehydration [ Meade and Jeanloz , 1991]; plastic instability and shear induced melting [ Griggs and Baker , 1969; McKenzie and Brune , 1972; Ogawa , 1987; Hobbs and Ord , 1988; Lomnitz‐Adler , 1990; Spray , 1993; Kikuchi and Kanamori , 1994; Kanamori et al , 1998; Bina , 1998a]; reactivation of preexisting fault planes [ Silver et al , 1995]; grain‐size reduction causing rheology changes [ Riedel and Karato , 1996, 1997; Karato et al , 2001]; and slab stresses due to an increase in mantle viscosity at 660 km [ Vassiliou et al , 1984; Goto et al , 1987; Vassiliou and Hager , 1988]. Observations show that the largest recent deep event, the 1994 Bolivia earthquake, occurred at the bottom of the subduction zone, that several large earthquakes (1994 Fiji and 1996 Flores Sea, Indonesia [e.g., Tibi et al , 1999]) may have ruptured outside the inner core of the slab as defined by previously located seismicity, and that deep seismicity occurs in areas which may be too warm for olivine to exist metastability.…”

Section: Introductionmentioning

confidence: 99%

Seismic constraints on mechanisms of deep earthquake rupture

Estabrook

2004

J. Geophys. Res.

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[1] Observations of the depth distribution of seismicity suggest that several mechanisms cause deep earthquakes. Cold subducting slabs exhibit a broad peak in seismicity between 300 and 530 km depth that is best explained by transformational faulting of metastable olivine. Cumulative seismic moment release increases sharply at $530 km depth in both cold and warm slabs, implying that events deeper than this are controlled by an equilibrium rather than a metastable phase change, which would be temperaturedependent. This, together with the observation that deep seismicity predominates near the garnet-rich upper boundary of the subducting plate (former oceanic crust), suggests that the transformation of garnet to perovskite, which may release considerable water, is integral in the cause of earthquakes deeper than 530 km, where most deep earthquakes occur.

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Are deep focus earthquakes caused by a martensitic transformation?

Cited by 11 publications

References 34 publications

Topography of the transition zone seismic discontinuities

Topography of the transition zone seismic discontinuities

Body wave inversion of the 1970 and 1963 South American large deep‐focus earthquakes

Seismic constraints on mechanisms of deep earthquake rupture

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