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

Recent revisions to the geomagnetic time scale indicate that global plate motion model NUVEL-1 should be modified for comparison with other rates of motion including those estimated from space geodetic measurements. The optimal recalibration, which is a compromise among slightly different calibrations appropriate for slow, medium, and fast rates of seafloor spreading, is to multiply NUVEL-1 angular velocities by a constant, α, of 0.9562. We refer to this simply recalibrated plate motion model as NUVEL-1A, and give correspondingly revised tables of angular velocities and uncertainties. Published work indicates that space geodetic rates are slower on average than those calculated from NUVEL-1 by 6±1%. This average discrepancy is reduced to less than 2% when space geodetic rates are instead compared with NUVEL-1A.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/94GL02118%4010.1002/%28ISSN%291944-8007.GRL40

Effect of recent revisions to the geomagnetic reversal time scale on estimates of current plate motions

The chemical composition of subducting sediment and its consequences for the crust and mantle

The overall mechanics of fold-and-thrust belts and accretionary wedges along compressive plate boundaries is considered to be analogous to that of a wedge of soil or snow in front of a moving bulldozer. The material within the wedge deforms until a critical taper is attained, after which it slides stably, continuing to grow at constant taper as additional material is encountered at the toe. The critical taper is the shape for which the wedge is on the verge of failure under horizontal compression everywhere, including the basal decollement. A wedge of less than critical taper will not slide when pushed but will deform internally, steepening its surface slope until the critical taper is attained. Common silicate sediments and rocks in the upper 10-15 km of the crust have pressure-dependent brittle compressive strengths which can be approximately represented by the empirical Coulomb failure criterion, modified to account for the weakening effects of pore fluid pressure. A simple analytical theory that predicts the critical tapers of subaerial and submarine Coulomb wedges is developed and tested quantitatively in three ways: First, laboratory model experiments with dry sand match the theory. Second, the known surface slope, basal dip, and pore fluid pressures in the active fold-and-thrust belt of western Taiwan are used to determine the effective coefficient of internal friction within the wedge,/x = 1.03, consistent with Byerlee's empirical law of sliding friction,/at, = 0.85, on the base. This excess of internal strength over basal friction suggests that although the Taiwan wedge is highly deformed by imbricate thrusting, it is not so pervasively fractured that frictional sliding is always possible on surfaces of optimum orientation. Instead, the overall internal strength apparently is controlled by frictional sliding along suboptimally oriented planes and by the need to fracture some parts of the observed geometrically complex structure for continued deformation. Third, using the above values of/at, and/x, we predict Hubbert-Rubey fluid pressure ratios X = Xt, for a number of other active subaerial and submarine accretionary wedges based on their observed tapers, finding values everywhere in excess of hydrostatic. These predicted overpressures are reasonable in light of petroleum drilling experience in general and agree with nearby fragmentary well data in specific wedges where they are available. The pressure-dependent Coulomb wedge theory developed here is expected to break down if the decollement exhibits pressure-independent plastic behavior because of either temperature or rock type. The effects of this breakdown are observed in the abrupt decrease in taper where wedge thicknesses exceed about 15 km, which is the predicted depth of the brittle-plastic transition in quartz-rich rocks for typical geothermal gradients. We conclude that fold-and-thrust belts and accretionary wedges have the mechanics of bulldozer wedges in compression and that normal laboratory fracture and frictional strengths are appropriate to mountain-building processes in the upper crust, above the brittle-plastic transition.

/pdf/mechanics-of-fold-and-thrust-belts-and-accretionary-wedges-39mfymsp74.pdf

Mechanics of fold-and-thrust belts and accretionary wedges

Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacific: computer-based reconstructions, model and animations

We investigate angular velocity vectors of the Philippine Sea (PH) plate relative to the adjacent major plates, Eurasia (EU) and Pacific (PA), and the smaller Caroline (CR) plate. Earthquake slip vector data along the Philippine Sea plate are inverted, subject to the constraint that EU-PA motion equals that predicted by the global relative plate model NUVEL-1. The resulting solution fails to satisfy geological constraints along the Caroline-Pacific boundary: convergence along the Mussau Trench and divergence along the Sorol Trough. We then seek solutions satisfying both the CR-PA boundary conditions and the Philippine Sea slip vector data, by adjusting the PA-PH and EU-PH best fitting poles within their error ellipses. We also consider northern Honshu to be part of the North American plate and impose the constraint that the Philippine Sea plate subducts beneath northern Honshu along the Sagmi Trough in a NNW-NW direction. Of the solutions satisfying these conditions, we select the best EU-PH as 48.2 deg N, 157.0 deg E, 1.09 deg/my, corresponding to a pole far from Japan and south of Kamchatka, and PA-PH, 1.2 deg N, 134.2 deg E, 1.00 deg/my. Predicted NA-PH and EU-PH convergence rates in central Honshu are consistent with estimated seismic slip rates. Previous estimates of the EU-PH pole close to central Honshu are inconsistent with extension within the Bonin backarc implied by earthquake slip vectors and NNW-NW convergence of the Bonin forearc at the Sagami Trough.

A model for the motion of the Philippine Sea Plate consistent with NUVEL‐1 and geological data

Paleogeographic reconstruction and origin of the Philippine Sea

The instantaneous rotation vector of the philippine sea plate relative to the eurasian plate

The plate geometry in northeast Asia has been a long-standing question, with a major issue being whether the Sea of Okhotsk and northern Japanese islands are better regarded as part of the North American plate or as a separate Okhotsk plate. This question has been difficult to resolve, because earthquake slip vectors along the Kuril and Japan trenches are consistent with either Pacific-North America or Pacific-Okhotsk plate motion. To circumvent this difficulty, we also use slip vectors of earthquakes along Sakhalin Island and the eastern margin of the Japan Sea and compare them to the predicted Eurasia-Okhotsk and Eurasia-North America motions. For a model with a separate Okhotsk plate, we invert 10 Eurasia-Okhotsk and 255 Pacific-Okhotsk slip vectors with Pacific-North America and Eurasia-North America NUVEL-1 data. Alternatively, for a model without an Okhotsk plate, those Eurasia-Okhotsk and Pacific-Okhotsk data are regarded as Eurasia-North America and Pacific-North America data, respectively. The model with an Okhotsk plate fits the data better than one in which this region is treated as part of the North American plate. Because the improved fit exceeds that expected purely from the additional plate, the data indicate that the Okhotsk plate can be resolved from the North American plate. The motions on the Okhotsk plate's boundaries predicted by the best fitting Euler vectors are generally consistent with the recent tectonics. The Eurasia-Okhotsk pole is located at northernmost Sakhalin Island and predicts right-lateral strike slip motion on the NNE striking fault plane of the May 27, 1995, Neftegorsk earthquake, consistent with the centroid moment tensor focal mechanism and the surface faulting. Along the northern boundary of the Okhotsk plate, the North America-Okhotsk Euler vector predicts left-lateral strike slip, consistent with the observed focal mechanisms. On the NW boundary of the Okhotsk plate, the Eurasia-Okhotsk Euler vector predicts E-W extension, discordant with the limited focal mechanisms and geological data. This misfit may imply that another plate is necessary west of the Magadan region in southeast Siberia, but this possibility is hard to confirm without further data, such as might be obtained from space-based geodesy.

Can the Okhotsk Plate be discriminated from the North American plate

[1] Dehydration embrittlement of metamorphosed oceanic crust and mantle in the subducting slab may be responsible for the occurrence of intermediate-depth earthquakes. We explore the possibility that this hypothesis can explain the morphology of the double seismic zones observed in northeast Japan, southwest Japan, northeast Taiwan, northern Chile, Cape Mendocino, and eastern Aleutians. We calculate transient temperature structures of slabs based on geologically estimated subduction histories of these regions. We then determine dehydration loci of metamorphosed oceanic crust and serpentinized mantle using experimentally derived phase diagrams. The depth range of the dehydration loci of metamorphosed oceanic crust and serpentine is dependent on slab age. The dehydration loci of serpentine produce a double-layered structure. Because the upper dehydration loci of serpentine are mostly located in the wedge mantle above the slab, we regard the upper plane seismicity representing dehydration embrittlement in the oceanic crust, and we fix the slab geometry so that the upper plane seismicity is just below the upper surface of the slab. We find that the lower plane seismicity is located at the lower dehydration loci of serpentine, which indicates that the morphology of the double seismic zones is consistent with the dehydration embrittlement.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002JB001918

Tetsuzo Seno

Papers

A model for the motion of the Philippine Sea Plate consistent with NUVEL‐1 and geological data

Paleogeographic reconstruction and origin of the Philippine Sea

The instantaneous rotation vector of the philippine sea plate relative to the eurasian plate

Can the Okhotsk Plate be discriminated from the North American plate

Double seismic zone and dehydration embrittlement of the subducting slab