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Proposal for describing the uniaxial compression behaviour in the model of internal structure A working group of the German Association for Water, Wastewater and Waste (DWA) is elaborating new recommendations for highly deformable cut‐off walls. An important goal is the utilization of the plastic material behaviour of highly deformable cut‐off walls. The article presents a new model to characterize the distinct nonlinear‐plastic mechanical behaviour of such materials, especially in the context of uniaxial compression. The "model of the internal structure" in this form takes up basic descriptions from models developed especially in Japan in the 1960s and 70s for directional load transfer based on contact orientation in dry granular aggregates and extends them by an approach to take cohesive material properties into account. [ABSTRACT FROM AUTHOR]

We evaluate seismicity and tectonics along the San Andreas Fault (SAF) in southern California to elucidate ongoing near‐field crustal deformation processes. The principal slip surfaces (PSSs) or the fault core that accommodate major earthquakes, form the boundary between the tectonic plates. We analyze seismicity catalogs extending back to 1857, 1932, and 1981 with progressively improved magnitude of completeness and spatial resolution. The 1857 to present statewide catalog that is complete at M5.5+ documents minimal aftershock activity for the Mw7.9 1857 and 1906 Mw7.8 San Francisco earthquakes. The higher quality 1932 and 1981 catalogs show that the PSSs (the rupture zone) of the 1857 Mw7.9 Fort Tejon earthquake exhibits remarkable seismic quiescence both in the core and in the adjacent extended‐damage zone. Further south, the fault core is still aseismic but the shape of the SAF is more complex, and the rate of adjacent seismicity is much higher. This fault complexity and the seismicity rate are larger the more the strike of the SAF deviates from the Pacific plate velocity‐vector direction. The focal mechanisms of the SAF adjacent earthquakes are also heterogeneous and rarely have strikes and dips that are consistent with slip on the nearby PSSs. We infer that the southern SAF is locked, and a lack of seismicity at the core of the fault may be a standard feature of faults that almost exclusively accommodate high‐slip rates by producing major earthquakes. Correspondingly future aftershock sequences of major earthquakes on the southern SAF will likely have below average aftershock productivity. Plain Language Summary: The fast‐moving San Andreas Fault (SAF) that runs up the spine of California from the Salton Sea to Cape Mendocino, forms the plate boundary between the Pacific and North America plates. It has accommodated California's two largest earthquakes, the 1857 Mw7.9 Fort Tejon and the 1906 Mw7.8 San Francisco, which ruptured the fault for hundreds of kilometers. We focus on analyzing the seismicity of the southern SAF from 1857 to present. Almost no small earthquakes occur along the core of the southern SAF, from south of Parkfield to the Salton Sea. To the north, the 1857 Mw7.9 earthquake was followed by relatively few immediate aftershocks, and since 1932 this section of the fault has been very seismically quiescent. To the south of the 1857 rupture, the rate of extended‐damage zone seismicity inversely correlates with the SAF strike deviation from the Pacific plate vector relative to the SAF strike. In particular, the east‐west striking 28 km long Mill Creek segment may impede SAF slip, which results in abundant off‐fault seismicity and transfer of tectonic strain into the eastern California shear zone and the Peninsular Ranges. Key Points: The near‐field seismicity of the southern San Andreas Fault (SAF) is limited to the adjacent extended‐damage zone and mostly absent from the fault coreStep changes in the 95% depth and in the texture of seismicity depth distribution likely define the presence of the SAF fault coreSeismicity rate in the damage zone positively correlates with SAF deviation from Pacific plate vector except in the quiescent 1857 rupture [ABSTRACT FROM AUTHOR]

Vibration‐based stress state identification method for iron and steel truss structures The assessment of the load‐bearing capacity of existing iron and steel truss structures is significantly dependent on the determination of the axial forces and corresponding stresses in axially loaded structural members. The axial forces in truss structures can be estimated by static calculations if accurate information about the structure and external loads are known. However, the stress condition for historical constructions can usually only be estimated inaccurately due to uncertainty in the assumptions of a static model. As an alternative to static calculations, non‐destructive measurement based techniques can be used. The newly developed methodology is based on vibration measurements and the finite element model updating. The member forces of the truss members can be calculated by means of an analytically based algorithm and a comparison between the numerically computed and experimentally identified natural frequencies and mode shapes of the truss structure as well as of selected individual members. For the tested structural systems, the identified axial forces by the proposed methodology agree well with the experimentally measured axial forces at different stress states. Furthermore, practical recommendations for the preparation of a measurement concept and development of design strategies for in‐situ investigations and safety assessment of existing iron and steel truss structures are given. [ABSTRACT FROM AUTHOR]

Three prolific earthquake swarms and numerous smaller ones have occurred since 1980 in the Mesozoic igneous plutonic rocks of the Perris block of the Peninsular Ranges, Southern California. The major swarms occurred in 1980–1981, 1983–1984, and 2016–2018, with the latest swarm still ongoing. These swarms have no clear mainshock, with the largest events of ML 3.6, ML 3.7, and Mw 4.4. Each successive swarm had larger cumulative seismic moment release with about 314 and 411 events of M ≥ 1.5, while the third swarm has produced about 451 events of M ≥ 1.5 (as of September 2018). The concurrent strike‐slip faulting occurred on north to northwest striking planes but with no orthogonal northeast trending seismicity alignments. These shallow swarms are probably driven by intrablock Pacific‐North America plate boundary stress loading of the two bounding major late Quaternary strike‐slip faults, the Elsinore and San Jacinto faults. The state of stress within the Cahuilla Valley pluton has a ~40° angle between the maximum principal stress and the average trend of the swarms, suggesting that migrating pore fluid pressures aid in the formation and growth of zones of weakness. These swarms, which last more than 600 days each, exhibit clear bilateral spatial migration for distances of up to ~7–8 km and reach their full length in about 20 months. The slow spatial‐temporal development of the swarms corresponds to a fluid diffusivity of 0.006 to 0.01 m2/s, consistent with very low permeability rocks as expected for this block. There is no geodetic or other evidence for a slow slip event driving the swarms. Plain Language Summary: There have been three unusual seismicity swarms in the Cahuilla Valley, Peninsular Ranges, over the last 40 years: 1980–1981, 1983–1984, and 2016–2018, with the latest still ongoing. They occurred within granite rocks that underlie the Cahuilla Valley pluton. The first two lasted for about 2 years, and the current swarm is still ongoing more than 2.5 years after it began. These swarms differ from mainshock‐aftershock sequences because the largest events occur months after the swarm initiation event. These swarms are probably driven by plate boundary stress loading of the two bounding major late Quaternary strike‐slip faults, the Elsinore and San Jacinto faults, and aided by changes in pore fluid pressures. Key Points: Since 1980, three prolific natural earthquake swarms occurred between the Elsinore and San Jacinto faults, in the central Peninsular RangesThese swarms are driven by interseismic plate boundary strain rates and modulated by pore fluid pressure in low‐permeability plutonic rockShallow depths, absence of mapped faults, and nonlinear seismic moment release suggest concurrent slip on foliations in the plutonic rock [ABSTRACT FROM AUTHOR]

In the automotive sector, dual phase (DP) steel grades have been increasingly used for various car body parts due to their good combination of strength and formability. To control mechanical and fracture characteristics of the DP steels, effects of martensitic phase fraction, morphology, and phase distribution must be understood. In this work, DP steel sheets with different martensitic phase fractions and ferritic grain sizes were produced through the intercritical annealing process. Likewise, FE simulations of 2D representative volume elements (RVEs) based on real micrograph were performed for all generated DP microstructures. Flow behaviors of single individual phases in the DP steels were described by a dislocation theory and local chemical compositions. Calculated stress-strain responses were verified with experimental results from tensile tests. Subsequently, stretch-forming tests under different states of stress using the Nakajima samples were carried out for the examined DP steels. Micromechanics RVE models were then applied to predict failure occurrences in the DP microstructures by considering plastic strain instability. Influences of morphologies and properties of constituent phases on localization due to incompatible deformation between martensite and ferrite were discussed with regard to governing stress states. [ABSTRACT FROM AUTHOR]

To reassess the main tectonic units and to quantify the slip partitioning within the overriding plate of the Tonga-Kermadec subduction zone, a seismotectonic study was performed using global seismicity and focal mechanisms catalogs. (1) New tectonic features were identified within the Lau Basin and the volcanic arc by remarkable shallow hypocenters alignments. (2) The Centroid Moment Tensor solutions catalog was processed in order to map the stress tensor variation in the upper plate. We found the tectonic features characterized by a diffuse seismicity are subjected to a composite stress regime and they are interpreted as diffuse immature plate boundaries controlled by the high thermal anomaly lying beneath the Lau Basin. (3) We quantified the margin-parallel rates of motion using the azimuth of the maximum compressive stress component computed within the interplate zone. The results highlight a major tectono-kinematic segmentation related to the subduction of the Louisville Seamount Chain. [ABSTRACT FROM AUTHOR]