This essential reference for graduate students and researchers provides a unified treatment of earthquakes and faulting as two aspects of brittle tectonics at different timescales. The intimate connection between the two is manifested in their scaling laws and populations, which evolve from fracture growth and interactions between fractures. The connection between faults and the seismicity generated is governed by the rate and state dependent friction laws - producing distinctive seismic styles of faulting and a gamut of earthquake phenomena including aftershocks, afterslip, earthquake triggering, and slow slip events. The third edition of this classic treatise presents a wealth of new topics and new observations. These include slow earthquake phenomena; friction of phyllosilicates, and at high sliding velocities; fault structures; relative roles of strong and seismogenic versus weak and creeping faults; dynamic triggering of earthquakes; oceanic earthquakes; megathrust earthquakes in subduction zones; deep earthquakes; and new observations of earthquake precursory phenomena.

The Mechanics of Earthquakes and Faulting

Two models, a simple cooling model and the plate model, have been advanced to account for the variation in depth and heat flow with increasing age of the ocean floor. The simple cooling model predicts a linear relation between depth and t½, and heat flow and 1/t½, where t is the age of the ocean floor. We show that the same t½ dependence is implicit in the solutions for the plate model for sufficiently young ocean floor. For larger ages these relations break down, and depth and heat flow decay exponentially to constant values. The two forms of the solution are developed to provide a simple method of inverting the data to give the model parameters. The empirical depth versus age relation for the North Pacific and North Atlantic has been extended out to 160 m.y. B.P. The depth initially increases as t½, but between 60 and 80 m.y. B.P. the variation of depth with age departs from this simple relation. For older ocean floor the depth decays exponentially with age toward a constant asymptotic value. Such characteristics would be produced by a thermal structure close to that of the plate model. Inverting the data gives a plate thickness of 125±10 km, a bottom boundary temperature of 1350°±275°C, and a thermal expansion coefficient of (3.2±1.1) × 10−5°C−1. Between 0 and 70 m.y. B.P. the depth can be represented by the relation d(t) = 2500 + 350t½ m, with t in m.y. B.P., and for regions older than 20 m.y. B.P. by the relation d(t) = 6400 - 3200 exp (−t/62.8) m. The heat flow data were treated in a similar, but less extensive manner. Although the data are compatible with the same model that accounts for the topography, their scatter prevents their use in the same quantitative fashion. Our analysis shows that the heat flow only responds to the bottom boundary at approximately twice the age at which the depth does. Within the scatter of the data, from 0 to 120 m.y. B.P., the heat flow pan be represented by the relation q(t) = 11.3/t½ μcal cm−2s−1. The previously accepted view that the heat flow observations approach a constant asymptotic value in the old ocean basins needs to be tested more stringently. The above results imply that a mechanism is required to supply heat at the base of the plate.

/pdf/an-analysis-of-the-variation-of-ocean-floor-bathymetry-and-4nps2wlqwq.pdf

An analysis of the variation of ocean floor bathymetry and heat flow with age

We present four companion digital models of the age, age uncertainty, spreading rates, and spreading asymmetries of the world's ocean basins as geographic and Mercator grids with 2 arc min resolution. The grids include data from all the major ocean basins as well as detailed reconstructions of back-arc basins. The age, spreading rate, and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading. Ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments. The age uncertainties for grid cells coinciding with marine magnetic anomaly identifications, observed or rotated to their conjugate ridge flanks, are based on the difference between gridded age and observed age. The uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities. Asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges, resulting in ridge jumps toward hot spots. We also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age-depth relationships. The new set of grids helps to investigate prominent negative depth anomalies, which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow. A combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems.

/pdf/age-spreading-rates-and-spreading-asymmetry-of-the-world-s-5bj3otyvfc.pdf

Age, spreading rates, and spreading asymmetry of the world's ocean crust

Seismic tomography based on P-wave travel times and improved earthquake locations provides further evidence for mantle-wide convective flow. The use of body waves makes it possible to resolve long, narrow structures in the lower mantle some of which can be followed to sites of present-day plate convergence at the Earth's surface. The transition from subduction-related linear structures in the mid-mantle to long-wavelength heterogeneity near the core-mantle boundary remains enigmatic, but at least some slab segments seem to sink to the bottom of the mantle.

/pdf/evidence-for-deep-mantle-circulation-from-global-tomography-3unqcjsa05.pdf

Evidence for deep mantle circulation from global tomography

Topographic data are combined with data on structure magmatism, seismicity, and paleomagnetism to support a simple kinematical model for the late Cenozoic evolution of the central Andes. The model interrelates Andean uplift, a changing geometry of the subducted Nazca plate, and a changing outline of the leading edge of the South American plate. It is argued that the late Cenozoic uplift of the Andes is a result of thermal thinning of the lithosphere and crustal thickening produced by crustal shortening.

/pdf/uplift-of-the-central-andean-plateau-and-bending-of-the-5kmhingx2v.pdf

Uplift of the Central Andean Plateau and bending of the Bolivian orocline

We made a region-by-region examination of subducted slab images along the circum-Pacific for some of the recent global mantle tomographic models, specifically for two high-resolution P velocity models and two long-wavelength S velocity models. We extracted the slab images that are most consistent among different models. We found that subducted slabs tend to be subhorizontally deflected or flattened in the upper and lower mantle transition region, the depth range of which corresponds roughly to the Bullen transition region (400–1000 km). The deflected or flattened slabs reside at different depths, either above or across the 660-km discontinuity as in Chile Andes, Aleutian, Southern Kurile, Japan, and Izu-Bonin; slightly below the discontinuity as in Northern Kurile, Mariana, and Philippine; or well below it as in Peru Andes, Java, and Tonga-Kermadec. There is little indication for most of these slabs to continue “directly” to greater depths well beyond the transition region. Mantle downflow associated with present slab subduction appears to be blocked strongly to turn into predominantly horizontal flow in the transition region. Recent global tomographic models show also a group of lithospheric slabs deeply sinking through the lower mantle, typically the presumed Farallon slab beneath North and Central America and the presumed Indian (Tethys) slab beneath Himalaya and the Bay of Bengal. These remnant slabs are not connected to the surface plates or to the presently subducting slabs and appear to sink independently from the latter. The presence of these deeply sinking slabs implies that the pre-Eocene subduction occurred in much the same way as in the present day to accumulate slab bodies in the transition region and that the consequent unstable downflow occurred extensively through the transition region in the Eocene epoch to detach many of the surface plates from the subducted slabs at depths and hence to cause the reorganization of global plate motion.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999RG000068

Stagnant slabs in the upper and lower mantle transition region

The P wave velocity structure beneath the Western Pacific is found from the International Seismological Center first arrival data. Special attention was paid to the deep structure beneath the Wadati-Benioff zone. We discretized the whole mantle into blocks with finer blocks in the region of interest to obtain the velocities of all the blocks. This way of discretization minimizes a problem with tomographic studies of regional scale: difficulty in making corrections for the effects outside the region of interest. Our solution is iterative with the alternate step of the relocation of earthquakes, using the whole mantle model of Inoue et al. (1990) as a starting model. A first-order smoothness constraint was imposed to suppress the possible fluctuation of the solution around the initial model. The essential result depends little on whether the reference spherical model is smooth or discontinuous near 400- and 670-km depths. We examined the resolution by calculating the resolving kernels for selected blocks and by reconstructing the checkerboard test patterns of velocity perturbation and the test structures of subducting lithosphere. The resolution is depth dependent but in general good enough to see the slab configuration beneath the Southern Kurile-Japan-Izu-Bonin arcs and the Java arc. It is relatively poor beneath the Northern Kurile and Mariana arcs. The seismic image of subducting slab beneath the Southern Kurile to Bonin arcs bends to subhorizontal near the leading edge of the Wadati-Benioff zone and extends continentward over a distance of more than 1000 km. The subhorizontal portion of the slab connects a high-velocity blob to the bottom that reaches a depth of at least 800 km across the 670-km discontinuity under the Japan arc. Although the image of the Java slab directly penetrates the 670-km discontinuity, it then bends to a shallow dip with a considerable spread, reaching a depth of about 1200 km. These results suggest that descending slabs of lithosphere in the Western Pacific tend to be stagnant in the transition zone under a subtle control of the 670-km discontinuity. Although stagnant slab materials eventually descend into the lower mantle, they no longer maintain their original configuration below the 670-km discontinuity.

Subducting slabs stagnant in the mantle transition zone

A new P wave tomographic model of the mantle was constructed using more than 10 million travel times The finite-frequency effect of seismic rays was taken into account by calculating banana-donut kernels at 2 Hz for all first arrival time data, and at 01 Hz for broadband differential travel time data Based on this model, a systematic survey for subducted slab images was developed for the circum-Pacific; including the Kurile, Honshu, Izu-Bonin, Mariana, Java, Tonga-Kermadec, southern and northern South America, and Central America, arcs This survey revealed a progressive lateral variation of the configuration of slabs along arc(s), which we interpret as an indication for successive stages of slab subduction through the Bullen's transition region with the 660 km discontinuity at the middle We identified the four distinct stages: I - slab stagnant above the 660 km discontinuity; II - slab penetrating the 660 km discontinuity; III - slab trapped in the uppermost lower mantle (at a depth of 660–1000 km); and IV - slab descending well into the deep lower mantle The majority of slab images are found to be either at Stage I or III, suggesting that Stages I and III are relatively stable or neutral and II and IV are relatively unstable or transient There is a remarkable distinction for the deepest hypocentral distribution between slabs at Stage I and slabs at Stages II or III

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2013JB010466

Subducted slabs stagnant above, penetrating through, and trapped below the 660 km discontinuity

A stagnant slab is a subducted slab of oceanic lithosphere subhorizontally deflected above, across, or below the 660 km discontinuity. This phenomenon has now been widely recognized beneath subduction zones around the circum-Pacific and in the Mediterranean. Collaboration of seismic and electromagnetic observations, mineral physics measurements, and geodynamic modeling has begun to provide a consistent picture of stagnant slab.

https://ir.lib.hiroshima-u.ac.jp/files/public/2/28632/20141016164917394655/AnnuRevEarthPlanetSci_37_19.pdf

Stagnant slab : A review

A tsunami earthquake is defined as a shock which generates extensive tsunamis but relatively weak seismic waves. A comparative study is made for the two recent tsunami earthquakes, and a subduction mechanism near a deep-sea trench is discussed. These two earthquakes occurred at extremely shallow depths far off the coasts of the Kurile Islands and of eastern Hokkaido on October 20, 1963, and on June 10, 1975, respectively. Both can be regarded as an aftershock of the preceding larger events. Their tsunami heights and seismic wave amplitudes are compared with those of the preceding events. The results show that the time constants involved in the tsunami earthquakes are relatively long but not long enough to explain the observed disproportionality between the tsunamis and the seismic waves. The process times are estimated to be less than 100 s. The spatio-temporal characteristics of the two events suggest that they represent a seaward and upward extension of the rupture associated with a great earthquake which did not break the free surface at the coseismic stage. The amplitude and phase spectra of long-period surface waves and the long-period P waveforms indicate that this extension of the rupture did not take place entirely along the lithospheric interface emerging as a trench axis. It rather branched upward from the interface in a complex way through the wedge portion at the leading edge of the continental lithosphere. This wedge portion consists in large part of thick deformable sediments. A large vertical deformation and hence extensive tsunamis result from such a branching process. A shallowest source depth, steepening of rupture surfaces, and a deformable nature of the source region all enhance generation of tsunamis. The wedge portion ruptured by a tsunami earthquake is usually characterized by a very low seismic activity which is presumably due to ductility of the sediments. We suggest that this portion fractures in a brittle way to generate a tsunami earthquake when it is loaded suddenly by the occurrence of a great earthquake and that otherwise it yields slowly. Upward branching of the rupture from the lithospheric interface produces permanent deformation of the free surface which is relative uplift landward and relative subsidence trenchward of the zone of surface break. This surface break zone geomorphologically corresponds to the lower continental slope between the deep-sea terrace and the trench. Such a mode of permanent deformation seems to be consistent with a rising feature of the outer ridge of the deep-sea terrace and a depressional feature of the trench. This consistency implies a causal relationship between great earthquake activities and geomorphological features near the trench.

Yoshio Fukao

Papers

Stagnant slabs in the upper and lower mantle transition region

Subducting slabs stagnant in the mantle transition zone

Subducted slabs stagnant above, penetrating through, and trapped below the 660 km discontinuity

Stagnant slab : A review

Tsunami earthquakes and subduction processes near deep-sea trenches