Partial Ruptures, Cascading Multi‐Fault Ruptures, and Aftershocks in 2D Random Fault Network

Using different grain-size granular mixtures (quartz and K-feldspar sand) in analogue extensional models

<p>Repeating earthquakes are thought to represent the repeated rupture of loaded patches surrounded by regions that are slipping aseismically; they provide a natural laboratory to study interactions between seismic and aseismic processes. These events occur less often than one would expect if these earthquakes accommodate all of the long-term slip. Recent crack models using rate-and-state friction<strong> </strong>(Cattania and Segall, 2019; Chen and Lapusta, 2009 ) suggest a possible explanation: for small events, a larger amount of the slip budget on the patch being taken up by aseismic slip. For larger events where most of the slip budget is seismic, the patch experiences partial ruptures, also leading to the deviation from expected scaling. We aim to test the predictions of this model of repeating ruptures by searching for the proposed partial ruptures. We choose to search using the Northern California earthquakes catalogue, which contains many well-located repeating earthquake sequences. Preliminary results suggest that partial ruptures in the Parkfield region are not common. If preliminary results pass additional tests, it may suggest that partial ruptures do not make up a significant proportion of the slip budget of larger repeating earthquakes in this region. </p>

Zou and Fialko (2024a), https://doi.org/10.1029/2024ea003824 analyzed the fault length statistics using several data sets spanning a wide range of length scales from millimeters to tens of kilometers, and concluded that the cumulative fault length distribution follows a universal power law with an exponent close to −2, implying that small faults can accommodate an appreciable fraction of tectonic strain. C. Scholz wrote a Comment in which he agrees with the main conclusions of our study, but questions the methodology that “fortuitously” gave rise to a correct answer. In particular, Scholz suggests that there is a spurious correlation in our estimation of the slope of a composite data set, which cancels out due to a lower‐dimensional sampling bias. Here we show that our estimated absolute value of the power law exponent of is not a result of normalizing the fault length‐frequency distribution by the map area, as suggested by Scholz. We also maintain that the lower‐dimensional bias is likely to decrease the estimated value of the power law exponent, but not by as much as 1 unit, so that the strain energy in the crust hosting the fault population remains finite. Estimating the magnitude of the lower dimensional bias for realistic fault distributions is important for distinguishing between the “inclusive correspondence” between faults and earthquakes, as proposed by Scholz in his Comment, and similar but distinct distributions of active and inactive faults, as proposed by Zou and Fialko (2024a), https://doi.org/10.1029/2024ea003824. This issue also directly bears on the amount of inelastic strain absorbed by small faults in developing shear zones.

The factors affecting prediction of LET spectra are discussed, namely the reaction cross sections and modelling of emitted charged particle spectra. The alpha particle spectrum from the 14N(n,2α) and 12C(n,3α) reactions is calculated assuming sequential break-up and either isotropic or anisotropic particle emission in the centre of mass, and examples are given for 20 MeV neutrons. The cross sections used in the LET predictive code NESLES are examined and updated, and the net effect on a 14 MeV neutron event size distribution is calculated. The different components of a 14 MeV event size distribution are identified. Finally, predicted and measured event size distributions for 14.2 MeV neutrons are compared.

In recent geothermal projects that were associated with induced seismicity it has been observed that the largest earthquake or earthquakes occurred after shut-in, the moment when the pressurised fluid injection in the borehole is stopped. We use a probabilistic approach based on Omori's law and a Gutenberg-Richter magnitude distribution to demonstrate that the probability of exceeding a certain maximum magnitude after shut-in is as high or higher than before stopping the fluid injection. The amount of this increase is dependent on the exponent of Omori's law q. For the reference case of q=2 and a 10% probability at shut-in time we obtain an increase to 14.6% for . If we consider a constant probability level of occurrence for an event larger than a given magnitude at shut-in time, this maximum magnitude increases by 0.12 units for . For the Fenton Hill experiment recent studies reveal q=7.5 that corresponds to only a small amount of probability increase for the post-injection phase.

We conducted a critical reexamination of Yamashita & Knopoff's (1987) models of aftershock occurrence, based on slow crack growth process. Such models assume that a time‐dependent process like slow crack growth, extensively documented at the sample scale, can be straightforwardly extrapolated to the field scale. If it is so, a question is rised : which model is the most consistent one with real data? We suggest here a possible way of discriminating between these models. The first model considers the slow growth of a main fracture surrounding small, locked asperities until slippage occurs. The second model considers the slow growth of satellite faults around the main fracture up to coalescence. By assuming power law distributions for the critical distances for quasistatic and dynamic crack growth, numerical simulations show that both models correctly predict Omori's law as well as the classical magnitude‐frequency law. Nevertheless, when looking further at the time distribution of aftershock magnitudes, it is shown that the results derived from the second model are inconsistent with usual observations since inverse sequence is predicted. Results derived from the first model are more realistic.

We computed moment (Mw) and local magnitude (ML) of about 250,000 earthquakes occurred in Italy from 2009 to 2018 and recorded at seismic stations of the Italian National Network managed by INGV.For moment magnitude computation, we start from raw velocity waveforms and invert the displacement spectra of more than 2,000,000 S-waves manually picked. We use the probabilistic method of Supino et al. [2019] to estimate the a-posteriori joint probability density function of the source parameters: seismic moment M0, corner frequency fc and high-frequency decay γ. Mw is obtained from M0 using the Kanamori [1977] equation.We start from the same waveforms to compute local magnitude using two designed on purpose codes, PyAmp and PyML [Di Stefano et al., 2023], and an attenuation law specific for the Italian region, Di Bona et al. [2016], obtaining ML values characterized by quality and homogeneity.Both magnitude catalogs can be reproduced due to the availability in open databases of all the input and output parameters used for processing.We observe a self-similar scaling between fc and M0 for Mw larger than ~2.0. For smaller magnitudes, S-wave spectra show an almost constant corner frequency (~10 Hz), which does not scale with the earthquake source (seismic moment). We interpret this as the constant cut-off frequency of the anelastic attenuation, which acts as a low-pass filter and produces an apparent corner frequency. The latter is lower than expected, and corresponds to an apparent larger source duration.Because of the conservation of total displacement integral after a low-pass filtering, signals must exhibit a maximum amplitude lower than expected to “compensate” the apparent larger source duration. ML values are therefore expected to be underestimated while moment magnitudes, by definition, are not affected by this as they are proportional to the displacement integral.Coherently, the comparison of our Mw and ML estimates shows the systematic underestimation of ML with respect to Mw for small magnitude events. The deviation from a 1:1 scaling relationship between ML and Mw overlaps the magnitude range where the constant apparent corner frequency arises in the M0-fc scaling (ML <~ 2).Regarding the upcoming of a new generation of earthquake catalogs characterized by very low completeness magnitudes (MC << 2), our results suggest that a robust analysis of the statistical features of these catalogs (e.g., event size distribution) should consider the use of a precise magnitude estimate such as Mw instead of ML.

SUMMARY The geometrical complexity of non-planar faults is known to affect not only fault slip rates but also crustal deformation and seismicity in the surrounding region, but implementing non-planar faults in numerical models has been challenging. We have developed a 3-D viscoelastoplastic finite element model to simulate long-term, steady-state fault slip along conceptual restraining bends and crustal deformation around them. By incorporating plastic yielding in both fault zones and the surrounding crust, this model can predict the quasi-steady state stress field and strain partitioning while avoiding pathological stress build-up encountered in traditional viscoelastic models. Here we detail the formulation of this model and explore major model parameters. The model results show that restraining bends tend to impede fault slip, increase shear stress in the surrounding crust and localize strain in a pair of belts off the fault zone. These effects are enhanced by high viscosity in the lower crust and upper mantle, high aspect ratio of bend width over fault length, fast relative motion of fault blocks and high fault friction. These model results may help explain the diffuse deformation surrounding the Big Bend of the San Andreas Fault and the more confined deformation around the Lebanon Bend of the Dead Sea Fault.

Insights into the 3D architecture of an active caldera ring-fault at Tendürek volcano through modeling of geodetic data

Seismic hazard calculation using the equivalent magnitude obtained from numerical modelling

This manuscript presents a universal control law for a class of complex dynamic systems, such as mobile robots. The trajectory tracking problem is among the major problems in the field of robotics. The proposed universal control law solves the trajectory tracking problem of mobile robots. Despite a large body of research on developing robot's control laws conducted in the literature, the dynamic effects of robots are often not taken into consideration while deriving control laws that define their trajectories. In most cases, the robot's trajectory tracking and/or stabilization problems are addressed based on its kinematic model due to simplicity. Therefore, the need for a universal control law based on the robot's dynamic and/or kinematic model is significant. Even though the feedback control theory is well-established in the field of robotics, the control laws for dynamic systems are typically more complex than system models themselves. Furthermore, control laws are required to be adapted depending on models of different mobile robot systems. Here, the development of universal control law is underscored, i.e., the paper is aimed at developing universal dynamic tracking control law that solves the trajectory tracking problem of a class of mobile robots. The controller is tested through a set of computer simulations using a differential drive mobile robot operating in an indoor planar environment.

The diverse mechanical behaviors of subduction zones during the seismic cycle emerge from the nonlinear dynamics of a complex mechanical system with interacting brittle and ductile deformation. The 2011 Tohoku mega-quake represents the culmination of a super-cycle of partial and full ruptures of the plate interface, but the physical controls on the down-dip segmentation of the megathrust remain unclear. Here, we propose a two-dimensional rheological model of the Japan trench to explain the variability of earthquake size at the Miyagi section, in northern Honshu, during the last century. We simulate seismicity in a continuum with a physics-based rate- and state-dependent constitutive law for fault slip, producing aperiodic earthquake sequences with a power-law distribution of rupture sizes. Although some partial ruptures of the megathrust are the result of self-emergent behavior, others are structurally controlled. The 1978 and 2005 Mjsim7 interplate earthquakes took place in a metamorphic belt in the mantle wedge corner bounded up-dip by the arc Moho that constitutes a permanent structural boundary. We explain the succession of the great 1981 Mw = 7.1 and 2003 Mw = 6.9 earthquakes within the forearc and the 2011 giant earthquake as the natural response of a large continuously velocity-weakening fault with a small nucleation size. The shallow segment below the frontal prism only slips in giant through-going ruptures that unzip the whole velocity-weakening interface. The model consistently explains the size, recurrence time, and hypocenter location of historical earthquakes in the Miyagi segment, the slow-slip and foreshock preparatory phase of the 2011 Tohoku earthquake, the large slip near the trench during the giant rupture, and important features of its postseismic deformation. The complex patterns of seismicity at the Japan trench can be better understood by assimilating geological and geophysical observations at various periods of the seismic cycle within an explicative physical framework.

We investigated frequency-magnitude distribution (FMD) of acoustic emissions (AE) occurring near an active mining front in a South African gold mine, using a catalog developed from an AE network, which is capable of detecting AEs down to M W −5. When records of blasts were removed, FMDs of AEs obeyed a Gutenberg−Richter law with similar b values, not depending on post-blasting time from the initial 1-min interval through more than 30 h. This result denies a suggestion in a previous study (Richardson and Jordan Bull Seismol Soc Am, 92:1766–1782, 2002) that new fractures generated by blasting disturb the size distribution of background events, which they interpreted as slip events on existing weak planes. Our AE catalog showed that the GR law with b ∼ 1.2 was valid between M W −3.7 and 0 for AEs around the mining front. Further, using the mine’s seismic catalog, which covers a longer time period of the same area, we could extend the validity range of the GR law with the same b value up to M W 1.

Employing numerical prediction models can be a powerful tool for forecasting air quality and visibility hazards related to dust events. However, these numerical models are sensitive to surface conditions. Roughness features (e.g., rocks, vegetation, furrows, etc.) that shelter or attenuate wind flow over the soil surface affect the magnitude and spatial distribution of dust emission. To aide in simulating the emission phase of dust transport, we used a previously published albedo-based drag partition parameterization to better represent the component of wind friction speed affecting the immediate soil sur-face. This report serves as a guide for integrating this parameterization into the Weather Research and Forecasting with Chemistry (WRF-Chem) model. We include the procedure for preprocessing the required input data, as well as the code modifications for the Air Force Weather Agency (AFWA) dust emission module. In addition, we provide an example demonstration of output data from a simulation of a dust event that occurred in the Southwestern United States, which incorporates use of the drag partition.

The emergence of a power-law distribution for the energy released during an earthquake is investigated in several models. Generic features are identified which are based on the self-affine behavior of the stress field prior to an event. This field behaves at large scale as a random trajectory in one dimension of space and a random surface in two dimensions. Using concepts of statistical mechanics and results on the properties of these random objects, several predictions are obtained and verified, in particular the value of the power-law exponent of the earthquake energy distribution (the Gutenberg-Richter law) as well as a mechanism for the existence of aftershocks after a large earthquake (the Omori law).