Physical Mechanism for a Temporal Decrease of the Gutenberg-Richter b-Value Prior to a Large Earthquake

Observations of seismicity prior to large earthquakes show that the slope of a Gutenberg-Richter magnitude-frequency relation, referred to as a b-value, sometimes decreases with time to the mainshock. Yet, underlying physical processes associated with the temporal change of a b-value remain unclear. Here we utilize continuum models of fully dynamic earthquake cycles with fault frictional heterogeneities and aim to simulate the temporal variation of a b-value. We first identify a parameter regime in which the model gives rise to an active and accelerating foreshock behavior prior to the mainshock. We then focus on the spatio-temporal pattern of the simulated foreshocks and analyze their statistics. We find that the b-value of simulated foreshocks decreases with time prior to the mainshock. A marked decrease in the resulting b-value occurs over the duration of less than a few percent of the mainshock recurrence interval, broadly consistent with foreshock behaviors and b-value changes as observed in nature and laboratory, rock-friction experiments. In this model, increased shear stresses on creeping (or velocity-strengthening) fault patches resulting from numerous foreshocks make these creeping patches more susceptible to future coseismic slip, increasing the likelihood of large ruptures and leading to a smaller b-value with time. This mechanism differs from a widely invoked idea that the decrease of a b-value is caused by a rapid increase in shear stress that promotes micro-crack growth, and offers a new interpretation of b-value changes prior to a large earthquake

Effects of Low‐Velocity Fault Damage Zones on Long‐Term Earthquake Behaviors on Mature Strike‐Slip Faults

Mature strike‐slip faults are usually surrounded by a narrow zone of damaged rocks characterized by low seismic wave velocities. Observations of earthquakes along such faults indicate that seismicity is highly concentrated within this fault damage zone. However, the long‐term influence of the fault damage zone on complete earthquake cycles, that is, years to centuries, is not well understood. We simulate aseismic slip and dynamic earthquake rupture on a vertical strike‐slip fault surrounded by a fault damage zone for a thousand‐year timescale using fault zone material properties and geometries motivated by observations along major strike‐slip faults. The fault damage zone is approximated asan elastic layer with lower shear wave velocity than the surrounding rock. We find that dynamic wave reflections, whose characteristics are strongly dependent on the width and the rigidity contrast of the fault damage zone, have a prominent effect on the stressing history of the fault. The presence of elastic damage can partially explain the variability in the earthquake sizes and hypocenter locations along a single fault, which vary with fault damage zone depth, width and rigidity contrast from the host rock. The depth extent of the fault damage zone has a pronounced effect on the earthquake hypocenter locations, and shallower fault damage zones favor shallower hypocenters with a bimodal distribution of seismicity along depth. Our findings also suggest significant effects on the hypocenter distribution when the fault damage zone penetrates to the nucleation sites of earthquakes, likely being influenced by both lithological (material) and rheological (frictional) boundaries.Plain Language SummaryLarge strike‐slip earthquakes tend to create a zone of fractured network surrounding the main fault. This zone, referred to as a fault damage zone, becomes highly localized as the fault matures, with a width of few hundred meters. The influence of this fault damage zone on earthquake characteristics remains elusive since we do not have enough long‐term observations along a single fault. We use numerical simulations to examine the behavior of earthquake nucleation and rupture dynamics on a fault surrounded by a damage zone over a thousand‐year timescale. Our simulations reveal that the reflection of seismic waves from the fault damage zone boundaries leads to complexity in earthquake sequences, such as variability in earthquake locations and sizes. We also show that a shallowfault damage zone produces shallower earthquakes with the earthquake depths centered around two locations (bimodal), as opposed to a deep fault damage zone with the earthquake depths centered around a single location (unimodal). Our study suggests that imaging the geometry and physical properties of fault damage zones could potentially give us clues about depths of future earthquakes and improve earthquake probabilistic hazard assessment.Key PointsFully dynamic earthquake cycle simulations show persistent heterogeneous stress distribution generated by fault zone wavesFaults surrounded by low‐velocity damage zones lead to more complexities in earthquakelocation, size, and slip patternsBoth lithology and rheology influence the depth distribution of seismicity, with shallow fault damage zones exhibiting bimodal distributionPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156497/2/jgrb54370.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156497/1/jgrb54370_am.pd

Towards inferring earthquake patterns from geodetic observations of interseismic coupling

Ultimately, seismotectonic studies seek to provide ways of assessing the timing, magnitude and spatial extent of future earthquakes. Ample observations document the spatial variability in interseismic coupling, defined as a degree of locking of a fault during the period of stress build-up between seismic events: fully or nearly locked fault patches are often surrounded by aseismically creeping areas. However, it is unclear how these observations could help assess future earthquakes. Here we simulate spontaneous seismic and aseismic fault slip with a fully dynamic numerical model. Our simulations establish the dependence of earthquake rupture patterns and interseismic coupling on spatial variations of fault friction. We consider the long-term evolution of slip on a model fault where two seismogenic, locked segments are separated by an aseismically slipping patch where rupture is impeded. We find that the probability for a large earthquake to break through the rupture-impeding patch is correlated with the interseismic coupling averaged over this patch. In addition, the probability that an earthquake breaks through the rupture-impeding patch and interseismic coupling are both related to fault friction properties through a single non-dimensional parameter. Our study opens the possibility of predicting seismic rupture patterns that a fault system can produce on the basis of observations of its interseismic coupling, and suggests that regions of low interseismic coupling may reveal permanent barriers to large earthquakes

Implementation of Do Not Attempt Resuscitate Orders in a Japanese Nursing Home

Objective: To investigate whether do not attempt resuscitation (DNAR) orders can be implemented in a standard nursing home in Japan, where routine DNAR orders are not yet common in many facilities including hospitals. Method: Ninety-eight residents in a 100-bed nursing home were evaluated. All of the eligible residents and/or their family members were asked whether they wanted to receive resuscitation, including mechanical ventilation. Result: The residents were 54 to 101 years of age (mean 83.3), with 27 males and 71 females. After administering the questionnaire, 92 (94%) patients did not want resuscitation and mechanical ventilation. Conclusion: In a nursing home, it was possible to obtain advance directives by which most residents/families rejected resuscitation and mechanical ventilation. This could avoid unnecessary and undesirable resuscitation procedures

Spatially Continuous Non-Contact Cold Sensation Presentation Based on Low-Temperature Airflows

Our perception of cold enriches our understanding of the world and allows us to interact with it. Therefore, the presentation of cold sensations will be beneficial in improving the sense of immersion and presence in virtual reality and the metaverse. This study proposed a novel method for spatially continuous cold sensation presentation based on low-temperature airflows. We defined the shortest distance between two airflows perceived as different cold stimuli as a local cold stimulus group discrimination threshold (LCSGDT). By setting the distance between airflows within the LCSGDT, spatially continuous cold sensations can be achieved with an optimal number of cold airflows. We hypothesized that the LCSGDTs are related to the heat-transfer capability of airflows and developed a model to relate them. We investigated the LCSGDTs at a flow rate of 25 L/min and presentation distances ranging from 10 to 50 mm. The results showed that under these conditions, the LCSGDTs are 131.4 $\pm$ 1.9 mm, and the heat-transfer capacity of the airflow corresponding to these LCSGDTs is an almost constant value, that is, 0.92.Comment: 7 page

Dynamic triggering of creep events in the Salton Trough, Southern California by regional M≥5.4M≥5.4 earthquakes constrained by geodetic observations and numerical simulations

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 427 (2015): 1-10, doi:10.1016/j.epsl.2015.06.044.Since a regional earthquake in 1951, shallow creep events on strike-slip faults within the Salton Trough, Southern California have been triggered at least 10 times by M ≥ 5.4 earthquakes within 200 km. The high earthquake and creep activity and the long history of digital recording within the Salton Trough region provide a unique opportunity to study the mechanism of creep event triggering by nearby earthquakes. Here, we document the history of fault creep events on the Superstition Hills Fault based on data from creepmeters, InSAR, and field surveys since 1988. We focus on a subset of these creep events that were triggered by significant nearby earthquakes. We model these events by adding realistic static and dynamic perturbations to a theoretical fault model based on rate- and state-dependent friction. We find that the static stress changes from the causal earthquakes are less than 0.1 MPa and too small to instantaneously trigger creep events. In contrast, we can reproduce the characteristics of triggered slip with dynamic perturbations alone. The instantaneous triggering of creep events depends on the peak and the time-integrated amplitudes of the dynamic Coulomb stress change. Based on observations and simulations, the stress change amplitude required to trigger a creep event of 0.01 mm surface slip is about 0.6 MPa. This threshold is at least an order of magnitude larger than the reported triggering threshold of non-volcanic tremors (2-60 KPa) and earthquakes in geothermal fields (5 KPa) and near shale gas production sites (0.2-0.4 kPa), which may result from differences in effective normal stress, fault friction, the density of nucleation sites in these systems, or triggering mechanisms. We conclude that shallow frictional heterogeneity can explain both the spontaneous and dynamically triggered creep events on the Superstition Hills Fault.This work was supported by NSF EAR awards 1246966 and 1411704 (M. Wei) and a Canada NSERC Discovery grant (Y. Liu)

Modeling of Upper Atmospheric Responses to Acoustic-Gravity Waves Generated by Earthquakes and Tsunamis

Recent studies have shown that upper atmospheric observations can be used to examine the properties of acoustic and gravity waves (AGWs) induced by natural hazards (NHs), including earthquakes and tsunamis (e.g., Komjathy et al., Radio Sci., 51, 2016). In addition to rapid processing, analysis, and retrieval of the AGW signals in data, the need remains to investigate a broad parameter space of atmospheric and ionospheric state observables for the robust constraint of coupled and nonlinear processes. Here, we present several earthquake/tsunami-atmosphere-ionosphere case studies that demonstrate the possibility to detect AGWs and constrain the characteristics of their sources. Direct numerical simulations of the triggering and wave dynamical processes, from Earth\u27s interior to the exobase, are carried out based on coupled forward seismic wave and tsunami propagation models and our state-of-the-art nonlinear neutral atmosphere and ionosphere models MAGIC and GEMINI (Zettergren and Snively, JGR, 120, 2015)

Cell type-dependent gene regulation by Staufen2 in conjunction with Upf1

<p>Abstract</p> <p>Background</p> <p>Staufen2 (Stau2), a double-stranded RNA-binding protein, is a component of neuronal RNA granules, which are dendritic mRNA transport machines. Although Stau2 is thought to be involved in the dendritic targeting of several mRNAs in neurons, the mechanism whereby Stau2 regulates these mRNAs is unknown. To elucidate the functions of Stau2, we screened for novel binding partners by affinity purification of GST-tagged Stau2 from 293F cells.</p> <p>Results</p> <p>Three RNA helicases, RNA helicase A, Upf1 and Mov10, were identified in Stau2-containing complexes. We focused our studies on Upf1, a key player in nonsense-mediated mRNA decay. Stau2 was found to bind directly to Upf1 in an RNA-independent manner <it>in vitro</it>. Tethering Stau2 to the 3'-untranslated region (UTR) of a reporter gene had little effect on its expression in HeLa cells. In contrast, when the same tethering assay was performed in 293F cells, we observed an increase in reporter protein levels. This upregulation of protein expression by Stau2 turned out to be dependent on Upf1. Moreover, we found that in 293F cells, Stau2 upregulates the reporter mRNA level in an Upf1-independent manner.</p> <p>Conclusions</p> <p>These results indicate that the recruitment of Stau2 alone or in combination with Upf1 differentially affects the fate of mRNAs. Moreover, the results suggest that Stau2-mediated fate determination could be executed in a cell type-specific manner.</p

Reconstruction of a phreatic eruption on 27 September 2014 at Ontake volcano, central Japan, based on proximal pyroclastic density current and fallout deposits

The phreatic eruption at Ontake volcano on 27 September 2014, which caused the worst volcanic disaster in the past half-century in Japan, was reconstructed based on observations of the proximal pyroclastic density current (PDC) and fallout deposits. Witness observations were also used to clarify the eruption process. The deposits are divided into three major depositional units (Units A, B, and C) which are characterized by massive, extremely poorly sorted, and multimodal grain-size distribution with 30–50 wt% of fine ash (silt–clay component). The depositional condition was initially dry but eventually changed to wet. Unit A originated from gravity-driven turbulent PDCs in the relatively dry, vent-opening phase. Unit B was then produced mainly by fallout from a vigorous moist plume during vent development. Unit C was derived from wet ash fall in the declining stage. Ballistic ejecta continuously occurred during vent opening and development. As observed in the finest population of the grain-size distribution, aggregate particles were formed throughout the eruption, and the effect of water in the plume on the aggregation increased with time and distance. Based on the deposit thickness, duration, and grain-size data, and by applying a scaling analysis using a depth-averaged model of turbulent gravity currents, the particle concentration and initial flow speed of the PDC at the summit area were estimated as 2 × 10−4–2 × 10−3 and 24–28 m/s, respectively. The tephra thinning trend in the proximal area shows a steeper slope than in similar-sized magmatic eruptions, indicating a large tephra volume deposited over a short distance owing to the wet dispersal conditions. The Ontake eruption provided an opportunity to examine the deposits from a phreatic eruption with a complex eruption sequence that reflects the effect of external water on the eruption dynamics.ArticleEarth, Planets and Space. 68: 82(2016)journal articl

Strong asymmetry in near-fault ground velocity during an oblique strike-slip earthquake revealed by waveform particle motions and dynamic rupture simulations

The 2022 Mw 7.0 Chihshang (Taiwan) earthquake, captured by almost a dozen near-fault strong-motion seismometers, high-rate GPS and satellite data, offers a rare opportunity to examine dynamic fault rupture in detail. Using dynamic rupture simulations, we investigate the particle motions recorded at near-fault strong-motion and 1 Hz GPS stations surrounding the main asperity. Some of these stations were as close as 250 m from the fault trace as determined by sub-pixel correlation of Sentinel-2 images. Our model reproduces the observed strong asymmetry in the ground motions on either side of the fault rupture, which results from along-dip spatial variability in rake angle on the steeply dipping fault (70°) at shallow depth (2 km). Observed near-fault, pulse-like fault-parallel ground velocity larger than fault-normal velocity can be explained by a model with a sub-shear rupture speed, which may be due to shallow rupture propagation within low-velocity material and to free surface reflections. In addition, we estimate a slip-weakening distance Dc of ~0.7-0.9m from strong-motion seismogram recorded at Station F073, which is located ~250 m from the fault rupture, and the results of dynamic rupture modeling. The inferred Dc is similar to other empirically derived estimates found for crustal earthquakes. These results have important implications for near-fault ground-motion hazard