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We use the technique of direct minimization of the Gibbs free energy of the 8-component (K2O-Na2O-Fe2O3-FeO-CaO-MgO-Al2O3-SiO2) multiphase system in order to determine the equilibrium mineral assemblages of rocks of different bulk chemical compositions equilibrated at various P-T conditions. The calculated modal compositions of rocks and experimental data on elastic moduli of single crystals are then used to calculate densities and isotropic elastic wave velocities of rocks together with their pressure and temperature derivatives. Sufficient accuracy of the calculations is confirmed by comparison with experimental data on the gabbro-eclogite transformation and precise ultrasonic measurements of elastic wave velocities in a number of magmatic and metamorphic rocks. We present calculated phase diagrams with isolines of density, elastic wave velocities, and their pressure and temperature derivatives for several anhydrous magmatic rocks, from granite to lherzolite. Density and elastic properties of rocks are controlled by their chemical compositions, especially the SiO2 content, and by P-T of equilibration, and they increase with pressure due to mineral reactions changing mineral assemblages from plagioclase-bearing and garnet-free to garnetbearing and plagioclase-free. TheV p -density correlation is high, and shows two clear trends: one for iron-poor ultramafic rocks and another for all the other rocks considered. Mineral reactions, which occur at high pressures, changeV p and density of anhydrous magmatic rocks following the well-known Birch (or a similar) law. Felsic, intermediate and mafic rocks can be well distinguished in theV p -V p /V s - diagram, although their values ofV p can be close to one another. TheV p -V p /V s -density diagrams together with calculated phase diagrams can serve as efficient instruments for petrologic interpretation of seismic velocities.

Submarine landslides can generate local tsunamis with high run-ups, posing a hazard to human lives and coastal facilities. Both ancient (giant Storegga slide off Norwegian coast, 8200 B. P.) and recent (Papua New Guinea, 1998) events show high potential danger of tsunamigenic landslides and the importance of mitigation efforts. This contribution presents newly discovered landslides 70 km off Padang (Western Sumatra, Indonesia) based on recent bathymetry measurements. This highly populated city with over 750,000 inhabitants exhibits high tsunami vulnerability due to its very low elevation. We model tsunamis that might have been induced by the detected landslide events. Estimations of run-up heights extrapolated from offshore tsunami amplitudes for Padang and other locations in the northern Mentawai fore-arc basin yield maximum values of about 3 m. We also provide a systematic parametric study of landslide-induced tsunamis, which allows us to distinguish potentially dangerous scenarios for Padang. Inside the fore-arc basin, scenarios involving volumes of 0.5–25 km³ could endanger Padang. Apart from slide volume, the hazard distribution mainly depends on three landslide parameters: distance to Padang, water depth in the generation region, and slide direction.

[1] Large submarine landslides can generate dangerous tsunamis. Because of their long-period signal, detection of landslides by common seismological methods is difficult. Here we suggest a method of detecting submarine landslides by using an array of land-based tiltmeters. The displacement of a large volume of sediments during landsliding produces a detectable elastic response of the lithosphere. We propose a technique to calculate this response and to invert for tsunami relevant parameters like slide location, volume, and velocity. We exemplify our method by applying it to the Storegga slide west of Norway and other tsunamigenic landslide events. The parameter which can be most robustly estimated from tiltmeter array measurements is the product of slide volume and its velocity (slide tsunamigenic potential). This parameter also controls the amplitude of the generated tsunami wave. The inversion accuracy of this parameter and the estimated tsunami height near the coast depends on the noise level of tiltmeter measurements, distance of the tiltmeters from the slide, and slide tsunamigenic potential itself. The tsunamigenic potential of the most dangerous slides like Storegga can be estimated well by tiltmeters at the coast if the effective noise level does not exceed 50 nrad.

Fault zones are the locations where motion of tectonic plates, often associated with earthquakes, is accommodated. Despite a rapid increase in the understanding of faults in the last decades, our knowledge of their geometry, petrophysical properties, and controlling processes remains incomplete. The central questions addressed here in our study of the Dead Sea Transform (DST) in the Middle East are as follows: (1) What are the structure and kinematics of a large fault zone? (2) What controls its structure and kinematics? (3) How does the DST compare to other plate boundary fault zones? The DST has accommodated a total of 105 km of left-lateral transform motion between the African and Arabian plates since early Miocene (similar to 20 Ma). The DST segment between the Dead Sea and the Red Sea, called the Arava/Araba Fault (AF), is studied here using a multidisciplinary and multiscale approach from the mu m to the plate tectonic scale. We observe that under the DST a narrow, subvertical zone cuts through crust and lithosphere. First, from west to east the crustal thickness increases smoothly from 26 to 39 km, and a subhorizontal lower crustal reflector is detected east of the AF. Second, several faults exist in the upper crust in a 40 km wide zone centered on the AF, but none have kilometer-size zones of decreased seismic velocities or zones of high electrical conductivities in the upper crust expected for large damage zones. Third, the AF is the main branch of the DST system, even though it has accommodated only a part (up to 60 km) of the overall 105 km of sinistral plate motion. Fourth, the AF acts as a barrier to fluids to a depth of 4 km, and the lithology changes abruptly across it. Fifth, in the top few hundred meters of the AF a locally transpressional regime is observed in a 100-300 m wide zone of deformed and displaced material, bordered by subparallel faults forming a positive flower structure. Other segments of the AF have a transtensional character with small pull-aparts along them. The damage zones of the individual faults are only 5-20 m wide at this depth range. Sixth, two areas on the AF show mesoscale to microscale faulting and veining in limestone sequences with faulting depths between 2 and 5 km. Seventh, fluids in the AF are carried downward into the fault zone. Only a minor fraction of fluids is derived from ascending hydrothermal fluids. However, we found that on the kilometer scale the AF does not act as an important fluid conduit. Most of these findings are corroborated using thermomechanical modeling where shear deformation in the upper crust is localized in one or two major faults; at larger depth, shear deformation occurs in a 20-40 km wide zone with a mechanically weak decoupling zone extending subvertically through the entire lithosphere.

[1] Since the devastating earthquake and tsunami in 2004 offshore Sumatra, many source models have been put forward. Recent studies clearly show that modern GPS-processing could achieve high resolving power for slip in near real time, which is crucial for determining tsunami initial conditions, provided accurate GPS-processing and inversion. Here, we propose an inversion technique with improved representation of the subduction zone geometry and physically justified boundary conditions. We show that the discrepancy between the inversion of near- and far field GPS data for the 2004 event, which is often explained by postseismic slip, can be eliminated by using our inversion method and IASP91 earth model. Inverted source models, including versions with splay faulting, are shown to be consistent with satellite altimetry data of offshore tsunami wave height, suggesting that displacement at the splay fault might have been present but was likely a second order process.

We employ high-resolution 2D thermomechanical modelling with complex elasto-visco-plastic rheology to analyse stresses in subducting and overriding plates. The model contains a dynamic subduction channel, defined as a few km thick zone of specific (weak) visco-plastic rheology between the slab and the overriding plate. Our high-resolution model corresponds to the zoom-in of the large-scale thermomechanical model of the Central Andes, with the 4-fold resolution increase. Initial model configuration (material, temperature and stress distributions) was interpolated from the parent model. Boundary conditions including slab pull and push velocities as well as velocity of the overriding plate, were also re-mapped from the large scale model. We demonstrate that, for shallow-dipping overridden slabs, the dominant stress is unbending stress at 50–100 km depth. This stress reaches 1–1.5 GPa and strongly prevails over the slab bending stress near the trench, which is limited by the frictional plastic yield. Unbending creates double (5–10 km distance between maximums) compression zone in the upper part of the slab and a zone of extension some 20–30 km below. Pressure in these zones differs from the lithostatic pressure to as much as plus/minus 0.8 GPa. Details of the distribution and magnitude of bending and unbending stresses in the slab are mainly controlled by the overriding velocity and direction of the slab-pull force. Overpressure in the subduction channel in all models does not exceed 100 MPa. Large over- and under-pressures in the slab, do not, however, lead to significant (more than 10 km) offsets of main dehydration reactions in crust and mantle of the slab.

A submarine landslide west of Spitsbergen could induce a destructive tsunami in the North Atlantic. Here we suggest an effective tool for early warning of tsunamis generated by huge underwater landslides. The method is based on the fact that a displacement of ~1000 km3 of sediment produces a permanent and detectable deformation of earth's lithosphere. We numerically model the ground tilting imposed by the hypothetical Spitsbergen landslide. Virtual inclinometers, positioned at the three distinct locations at Spitsbergen, show tilts up to 1000 nrad. The actual size of the submarine mass movement is assessable as soon as the sliding ceases, i.e. approximately after one hour, thus leaving another one hour warning time for northern Norway and two hours for Iceland and southern Norway.

[1] The 2004 catastrophic Indian Ocean tsunami has strongly emphasized the need for reliable tsunami early warning systems. Another giant tsunamigenic earthquake may occur west of Sumatra, close to the large city of Padang. We demonstrate that the presence of islands between the trench and the Sumatran coast makes earthquake-induced tsunamis especially sensitive to slip distribution on the rupture plane as wave heights at Padang may differ by more than a factor of 5 for earthquakes having the same seismic moment (magnitude) and rupture zone geometry but different slip distribution. Hence reliable prediction of tsunami wave heights for Padang cannot be provided using traditional, earthquake-magnitude-based methods. We show, however, that such a prediction can be issued within 10 minutes of an earthquake by incorporating special types of near-field GPS arrays (‘‘GPS-Shield’’). These arrays measure both vertical and horizontal displacements and can resolve higher order features of the slip distribution on the fault than the seismic moment if placed above the rupture zone or are less than 100 km away of the rupture zone. Stations in the arrays are located as close as possible to the trench and are aligned perpendicular to the trench, i.e., parallel to the expected gradient of surface coseismic displacement. In the case of Sumatra and Java, the GPS-Shield arrays should be placed at Mentawai Islands, located between the trench and Sumatra and directly at the Sumatra and Java western coasts. We demonstrate that the ‘‘GPS-Shield’’ can also be applied to northern Chile, where giant earthquakes may also occur in the near future. Moreover, this concept may be applied globally to many other tsunamigenic active margins where the land is located above or close to seismogenic zones.

The Andes were formed by Cenozoic tectonic shortening of the South American plate margin overriding the subducting Nazca Plate. Using coupled, thermo-mechanical, numerical modeling of the dynamic interaction between subducting and overriding plates, we searched for factors controlling the intensity of the tectonic shortening. From our modeling, constrained by geological and geophysical observations, we infer that the most important factor was fast and accelerating (from 2 to 3 cm yr(hoch)-1) westward drift of the South American Plate, whereas possible changes in the convergence rate were not as important. Other important factors are the crustal structure of the overriding plate and the shear coupling at the plate interface. The model in which the South American Plate has a thick (40-45 km at 35 Ma) crust and relatively high friction coefficient (0.05) at the Nazca-South American plate interface generates more than 300 km of tectonic shortening over the past 35 million years and replicates well the crustal structure and evolution of the high Central Andes, However, modeling does not confirm that possible climate-controlled changes to the sedimentary trench-fill during the last 30 million years might have significantly influenced the upperplate shortening rate. The model with initially thinner (less than 40 km) continental crust and a lower friction coefficient (less than 0.015) results in less than 40 ikm of shortening in the South American Plate, replicating the situation in the Southern Andes. During upper-plate deformation, the processes that cause a reduction in lithospheric strength and an increase in interplate coupling are particularly important. The most significant of these processes appears to be: (1) delamination of the lower crust and mantle lithosphere, driven by gabbro-eclogite transformation in the thickening lower crust, and (2) mechanical failure of the foreland sediments. The modeling demonstrates that delaminating lithosphere interacts with subduction-zone corner flow, influencing both the rate of tectonic shortening and magmatic-arc productivity, and suggests an anti-correlation between these two parameters. Our model also predicts that the down-dip limit of the frictional coupling domain between the Nazca and South American Plates should be ~15-20 km deeper in the Southern Andes (south of 28° S) compared to the high Central Andes, which is consistent with GPS and seismological observations.

We employed a 2D numerical thermo-mechanical modeling technique to study the dynamics of the plateau-foreland system, with particular application to the Central Andean back-arc. Our model back-arc consists of a weak plateau indented by a relatively stronger foreland. A "normal" shortening scenario implies pure-shear tectonic inflation of the plateau. Forces that drive tectonic shortening encounter major resistance from the growing gravitational potential of the rising plateau. Other resistance factors are the brittle strength of the upper crust and the viscous resistance of ductile lower crust and upper mantle. The overall resistance to shortening is up to 6-8x10(hoch)12N m(hoch)-1 for plateau heights of less than 5 km. Several thermo-mechanical processes within the back-arc have a gross weakening effect on a back-arc scale and, thus, may be responsible for episodes of shortening rate acceleration in the past. These processes include: (i) on-going eclogitization of the lower mafic crust beneath the plateau, (ii) heating and convection in the plateau felsic crust, (iii) mechanical failure of the foreland sediments and (iv) high erosion and exhumation rates at the plateau margin (effective in monsoon areas but apparently not relevant for the Central Andes). The largest reduction in the effective lithospheric strength (~3x10(hoch)12N m(hoch)-1,i.e.,40-50% of the total strength) could result from the mechanical failure of the foreland sediments, leading to the migration of shortening deformation into the Altiplano foreland (Subandean thrust belt). This failure implies a drastic reduction of both sediment cohesion (almost to zero values) and friction angle (to at least a third of the normal value of 30°). The second important factor is on-going eclogitization of the lower crust beneath the plateau, which increases the average density of the crust and thus prevents rising of the plateau. The eclogitization may decrease the effective lithospheric strenth by ~2x10(hoch)12N m(hoch)-1 (25-35% of the total strength). The third important factor is intracrustal convection, which follows eclogitization-driven lithospheric delamination and reduces the brittle strength of the uppermost crust (overall effect ~1x10(hoch)12N m(hoch)-1, or 10-15% of the total strength). High erosion rate at the plateau margin may efficiently weaken the orogenic lithosphere but, in the case of the low to moderate erosion rates typical of the Central Andes, its effect is negligible. In general, internal weakening of the overriding plate is, in addition to plate tectonic forces, among the major controls on the Andean orogeny.

The Andes, the world's second highest orogenic belt, were generated by the Cenozoic tectonic shortening of the South American plate margin overriding the subducting Nazca plate. We use a coupled thermomechanical numerical modeling technique to identify factors controlling the intensity of the tectonic shortening. From the modeling, we infer that the most important factor was accelerated westward drift of the South American plate; changes in the subduction rate were less important. Other important factors are crustal structure of the overriding plate and shear coupling at the plates' interface. The model with a thick (40–45 km at 30 Ma) South American crust and relatively high friction coefficient (0.05) at the Nazca–South American interface generates >300 km of tectonic shortening during 30–35 m.y. and replicates the crustal structure and evolution of the high central Andes. The model with an initially thinner (

In the deep crust, temperature, which is among the key parameters controlling lithospheric dynamics, is inferred by extrapolation from the surface using several assumptions that may well fail in regions of active tectonics and fluid migration. In the rare case that temperatures of 700°C or higher are exceeded in the upper/middle continental crust composed of quartz-rich felsic rocks, the α-β quartz transition (ABQT) will occur, generating a measurable seismic signature and offering the possibility for precisely estimating temperature from the known ABQT phase diagram. Here it is shown that all expected seismic features of the ABQT are met by the boundary between the upper and middle crust below the INDEPTH III profile in central Tibet. This implies that a temperature of 700°C is achieved at a depth of 18 km under the southern Qiangtang block, that agrees well with the depth to the top of a high electrical conductivity anomaly, likely representing partially melted crust. To the south in the northern Lhasa block, the ABQT lies at 32 km depth, corresponding to a temperature of 800°C. It thus appears that this seismic boundary representing the ABQT is the result of (recent) geological processes rather than being a lithological boundary.

Thermomechanical interaction of the low-angle subducting oceanic plate with the overriding continental plate may result in intensive tectonic shortening of the upper plate (subduction orogeny). Factors controlling such behaviour remain poorly understood. Here we present a fully coupled thermo-mechanical model of the extreme case of the subduction orogeny, a development of the more than 4 km high Altiplano-Puna plateau in the Central Andes in Cenozoic time. The same model attempts to explain present-day (GPS)deformation. Our 2-D finite element thermomechanical model explores the interaction of the subducting Nazca plate with the overriding South America (SA) plate in the 1200 km long and 400 km high model box. The model employs realistic stress- and temperature-dependent visco-elasto-plastic rheology, shear heating and gabbro-eclogite transformation. The velocities, at which overriding plate enters the model box and the subducting plate leaves the box, are prescribed by boundary conditions constrained by geological observations. The interface between the slab and the upper plate is modelled as a few kilometer thick subduction channel with the two optional rheologies: (i) the Mohr-Coulomb elasto-plastic rheology with the very low friction coefficient (less than 0.05), and (ii) temperature dependent viscous rheology similar to the reported rheology for the wet quartzite. At each modelling time step both rheologies are tested and the energetically more efficient rheology is used. The modelling results replicate well geological evolution of the Central Andes during the last 10 Myr if the overriding velocity of the stable SA is set to be high (25-30 mm/yr) and increasing with time, and friction coefficient in the subduction channel is set to 0.03-0.05. The same model replicates well also the GPS observations if small (10 percent of the value) temporal changes of the friction coefficient in the subduction channel are allowed, which generate a seismic cycle. Locking depth in such a model increases with decreasing friction coefficient in the subduction channel.

We present a set of self-consistent numerical experiments resulting in the development of local weak zones within a wide region of extending brittle lithosphere overlying viscous asthenosphere. In these two-dimensional models, the brittle yield strength is controlled by a Byerlee's Law friction coefficient and a value for cohesion. A portion of the brittle strength is reduced as a function of plastic strain (strain beyond yield). This strain weakening can result in concentration of strain on spontaneously formed weak zones accommodating dip slip, or model normal faults. The temperature-dependent viscous rheology is based on a laboratory-derived power-law creep flow law for diabase. The initial temperature gradient is taken to be linear with depth, and controls the depth range over which the viscosity decreases beneath the brittle lithosphere. The viscous flow of the transition region below the lithosphere can result in a distributed set of model normal faults, in some cases with regular periodic spacing. ...