Marine forearc structure of eastern Java and its role in the 1994 Java tsunami earthquake

We resolve a previously unrecognized shallow subducting seamount from a re-processed multichannel seismic depth image crossing the 1994 M7.8 Java tsunami earthquake slip area. Seamount subduction is related to the uplift of the overriding plate by lateral shortening and vertical thickening, causing pronounced back-thrusting at the landward slope of the forearc high and the formation of splay faults branching off the landward flank of the subducting seamount. The location of the seamount in relation to the 1994 earthquake hypocentre and its co-seismic slip model suggests that the seamount acted as a seismic barrier to the up-dip co-seismic rupture propagation of this moderate size earthquake. The wrapping of the co-seismic slip contours around the seamount indicates that it diverted rupture propagation, documenting the control of forearc structures on seismic rupture.

An Improved Quadtree Sampling Method for InSAR Seismic Deformation Inversion

With the development of interferometric synthetic aperture radar (InSAR), the seismic deformation observation density increases sharply. Data down-sampling can effectively reduce the observation density and the computational cost for subsequent researches. Considering the saliency of the deformation field, we introduce a saliency-based quadtree algorithm for down-sampling (SQS). Three simulation experiments show that SQS can effectively distinguish the near-field and far-field deformation, as well as reduce the amount of observation, while keeping the detailed information of the main deformation near the fault. SQS can avoid the interference of far-field local deformation better than the traditional quadtree sampling algorithm (QS), thus obtaining better inversion results. We took the Dingri earthquake on 20 March 2020 as a case study to verify the advantages of SQS in dealing with real earthquake deformation. We obtained the co-seismic deformation from the ascending and descending Sentinel-1 for the Dingri earthquake, using QS and SQS for sampling and inversion separately. The results show the advantages of SQS in data volume reduction, observation distribution, anti-interference of local deformation, and inversion accuracy. Our preferred solution based on SQS shows that the Dingri earthquake was caused by a normal fault slip. The main slip area is 2–5.5 km deep with a maximum slip of 0.68 m. The estimated geodetic moment is 3.14 × 1017 Nm, corresponding to a magnitude of Mw5.63.

High-resolution spatio-temporal fault slip using InSAR observations: insights on seismic and aseismic slip during a shallow crust earthquake swarm

<p>How earthquakes initiate and run-away into major ruptures is still a challenging research topic, that will benefit from increasing our capability to observe processes from the seismogenic source regions. In recent years, two models for earthquake nucleation have been proposed to explain earthquake sequences, a slow-slipping model and a cascade model, based mostly on the analysing seismic data. Here we use geodetic data to contribute to the study of seismogenic source regions during earthquake sequences. Earthquake swarms are unusual as they do not obey observational physics laws, e.g., Gutemberg-Richter law. This deviation might be to a disproportioned contribution of aseismic processes, and hence provide an opportunity to investigate the role of aseismic behaviour in the nucleation and propagation of earthquakes.</p><p>Here, we study a shallow seismic swarm in Nevada, USA, in 2011. We process satellite radar images to form differential interferograms and to quantify the surface displacements. From the interferograms, we observe a clear surface displacement signal (~4 cm in line-of-sight direction) consistent with slip along a N-S striking normal fault, before the largest magnitude event (M4.6) in the swarm. We also find that interferograms across the M4.6 are dominated by slip on a NE-SW striking fault. Thus, we consider slip along a fault system with a geometry consisting of two fault planes. To interpret the surface displacement, we invert for its optimal geometry directly using the interferometric wrapped phase. Based on the fault geometry together with inferred surface ruptures, we construct a smooth fault plane with triangular dislocations. Then, we extend our previous method to obtain distributed fault slip models from the wrapped phase. We implement a physics-based linear elastic crack model with no stress singularities, coupled with a linear time inversion with optimal regularization method to estimate the temporal evolution of fault slip. We apply this method to the 2011 Hawthorne swarm geodetic data to test the two conceptual earthquake nucleation and propagation models. The inversion reveals (1) two slip maxima; a narrow (1km<sup>2</sup>) slip area on the southern fault with high average slip (0.8m) occurring before the M4.6 event; and a wider (40km<sup>2</sup>) slip area on the northern fault which ruptured during and after the M4.6 event and with lower average slip (0.1m); (2) our results are more consistent with a cascade model of discrete slip patches, rather than a slow-slipping model thought as a growing elliptical crack; (3) the aseismic (geodetic) moment ratio is variable from 100% before the M4.6 event, but remains larger than 60% after it. </p><p>The study of the 2011 Hawthorne swarm allows us to illuminate fault slip in much greater detail than usually possible. We conclude that there were significant aseismic fault processes, most likely slow-slip or localized fluid-enhanced fault slip, along with discrete segments of the fault plane active before and after the largest earthquake in this swarm. This study contributes to highlighting the importance of using geodetic data to understand the role of aseismic processes during swarms. An important step towards improving our understanding of the nucleation and propagation of earthquakes.</p>

Shallow slow earthquakes to decipher future catastrophic earthquakes in the Guerrero seismic gap.

The Guerrero seismic gap is presumed to be a major source of seismic and tsunami hazard along the Mexican subduction zone. Until recently, there were limited observations to describe the shallow portion of the plate interface in Guerrero. For this reason, we deployed offshore instrumentation to gain new seismic data and identify the extent of the seismogenic zone inside the Guerrero gap. We discovered episodic shallow tremors and potential slow slip events which, together with repeating earthquakes, seismicity, residual gravity and residual bathymetry suggest that a portion of the shallow plate interface in the Guerrero seismic gap undergoes stable slip. This mechanical condition may not only explain the long return period of large earthquakes with origins inside the Guerrero seismic gap, but also reveal why the rupture from past M<8 earthquakes on adjacent megathrust fault segments did not propagate into the gap to encompass a larger slip area. Nevertheless, a large enough earthquake initiating nearby could rupture through the entire Guerrero seismic gap if driven by dynamic rupture effects.

On the heterogeneity of the earthquake rupture

Summary The scaling of earthquake parameters with seismic moment and its interpretation in terms of self-similarity is still debated in the literature. We address this question by examining a worldwide compilation of corner frequency-based and elastic rebound theory (ERT)-based fault slip, area and stress drop values for earthquakes ranging in magnitude from -0.7 to 7.8. We find that corner frequency estimates of slip (and stress drop) scale differently than those inferred from the ERT approach, where the latter deviates from the generally accepted constant stress drop behavior of so-called self-similar scaling models. We also find that average slips from finite-source models are consistent with corner frequency scaling, whereas peak slip values are more consistent with the ERT scaling. The different scaling of corner frequency- and ERT-based estimates of slip and stress drop with earthquake size is interpreted in terms of heterogeneity of the rupture process. ERT-based estimates of stress drop decrease with seismic moment suggesting a self-affine behavior. Despite the inferred heterogeneity at all scales, we do not observe a clear effect on the Brune stress drop scaling with earthquake size.

Optimization and Design of a Railway Wheel Profile Based on Interval Uncertainty to Reduce Circular Wear

Wheel tread wear is a form of wheel damage that can seriously affect the performance of freight vehicles. A new numerical approach to optimizing wheel profiles can reduce circular wear on the LM wheel in the design cycle. This approach considers the influence of different line conditions and speed fluctuation on wheel wear, along with the performance of the wheel and the rail as the materials wear. In this approach, a nonlinear numerical optimization model for the wheel tread profile is built through a backpropagation (BP) neural network method. The multipoint Kik–Piotrowski (KP) contact mechanics model is applied to calculate the wheel/rail normal force, tangential creep force, the stick-slip area, and the size and shape of the contact patch. The optimal profile is obtained through the genetic algorithm (GA) method. In order to better reflect the random characteristics of wheel/rail matching and interval uncertainty, a random sampling technique is used to generate a random data sample at typical operating speeds.

Identifikasi Bidang Gelincir Zona Rawan Longsor Menggunakan Metode Geolistrik Di Ruas Jalan Toraja – Mamasa

Abstrak. Metode geolistrik tahanan jenis merupakan salah satu dari metode geofisika yang dapat mendeteksi aliran listrik di bawah permukaan bumi. Salah satu aplikasi metode geolistrik tahanan jenis adalah dapat mengidentifikasi bidang gelincir pada daerah rawan longsor. Penelitian ini bertujuan untuk mengetahui bidang gelincir pada daerah rawan lonsor di ruas jalan Toraja – Mamasa. Hasil dari pengukuran geolistrik tahanan jenis dipadukan dengan hasil pengeboran di beberapa titik agar tidak terjadi kesalahan dalam proses interpretasi batuan yang diduga sebagai penyebab terjadinya tanah longsor. Informasi tentang perlapisan tanah tersebut digunakan untuk mengetahui batas-batas ketidakstabilan pada lapisan tanah yang dapat menjadi acuan dalam pengembangan wilayah, khususnya ruas jalan Toraja - Mamasa. Dalam penelitian ini diperoleh nilai resistivitas yang berbeda-beda untuk setiap batuan. Variasi resistivitas yang diperoleh dimulai dari 0 – 978 Ωm. Nilai resistivitas batuan pada bidang gelincir di lokasi penelitian berada pada bidang batas 50-300 Ωm. Batuan penyusunnya berupa batupasir lempung, lava andesit dan basalt. Abstract The resistivity geoelectric method is one of the geophysical methods that can detect the flow of electricity below the earth's surface. One application of the resistivity geoelectric method is to identify the slip field in landslide prone areas. The research aimed to discover slip area of landslide prone zone at the segment road of Toraja-Mamasa. The results of the geoelectric resistivity measurements are combined with the results of drilling at several points so that there are no errors in the process of rock interpretation which are thought to be the cause of landslides. Information about the soil layers is used to determine the boundaries of instability in the soil layer which can be used as a reference in regional development, especially the Toraja - Mamasa road segment. In this research, it was obtained different resistivity values for each rock. The resistivity variation obtained started from 0 - 978 Ωm. The rock resistivity value in the slip plane at the research location is in the 50-300 Ωm boundary fields. The rocks lithologies are clay sandstones, andesite lava and basalt.

Criteria of Mora-Coulomb with Three Parameters of Material

A modified Mohr – Coulomb criterion is presented. This criterion, in addition to adhesion and the angle of internal friction, contains the third parameter of the material (d). Depending on the value of this parameter (d), the modified criterion can take the form of the original Mohr – Coulomb criterion (with d = 0.5) or the original Treska criterion (with d = 0). For all other values of the parameter (d), varying in the range of 0 <d <0.5, the tangential stresses by the modified criterion are larger than the Mohr – Coulomb criterion, but less than the Tresca criterion. The paper presents the methodology and results of determining this parameter (d) using experiments on the triaxial compression of soils. The technique contains recommendations for the appointment the value of the axial strain of the sample material when determining the value of the parameter d. The value of the ultimate deformation is advisable to take in the range from 8 to 12%. This range is due to the fact that with axial deformation of the sample of 8%, the formation of slip areas begins in it, and with axial deformation of the sample 12%, the slip area is completely formed. In this case, the parameter d varies in the range 0 <d <0.5, having a shear strength bigger than in the Tresca criterion, but less than in the original Mohr – Coulomb criterion. The tangential stresses according to the modified criterion, on the contrary, have a bigger value than according to the Mohr – Coulomb criterion, but the values of the tangential stresses are lower than in the Tresca criterion.