Transient Stress Changes Research Articles

Microseismicity at the Time of a Large Creep Event on the Calaveras Fault is Unresponsive to Stress Changes

The potential relationship between surface creep and deeper geological processes is unclear, even on one of the world’s best-studied faults. From June to August 2021, a large creep event with surface slip of more than 16 mm was recorded on the Calaveras fault in California, part of the San Andreas fault system. This event initially appeared to be accompanied by along-fault migration of seismicity, suggesting it penetrated to depth. Other studies have suggested that surface creep events are likely a shallow feature, unrelated to deep seismicity. To provide more detail on the relationship between earthquakes, surface creep, and potential aseismic slip at seismogenic depth, we tripled the number of earthquakes in the Northern California Earthquake Catalog in the region of the creep event for all of 2021. This was accomplished by implementing earthquake detection techniques based on both template matching (EQCorrscan) and AI-based automatic earthquake phase picking (PhaseNet). After manual inspection, the detected earthquakes were first located using Hypoinverse and subsequently relocated via GrowClust. Our enhanced catalog indicates that the spatiotemporal pattern of earthquakes here is not strongly influenced by the creep event and is better explained by structural heterogeneity than transient stress changes, indicating a decoupling of seismicity rate and surficial creep on this major fault.

Geometrically controlled slow slip enhanced by seismic waves: A mechanism for delayed triggering

Seismic waves generated during earthquakes induce transient stress changes in the crust. These ephemeral perturbations can trigger critically stressed asperities at remote distances, often with significant time delays. The physical mechanism that governs this phenomenon is not completely resolved. Numerical simulations of dynamic perturbations passing along a heterogeneous pre-stressed fault, demonstrate that weak portions of the fault that host ongoing slow slip can transfer stress in response to the perturbations, loading asperities poised for failure. We find that the magnitude of perturbation, the state of the asperity, as well as deformation of the surrounding material, jointly control the delay time between perturbation and triggered event. The slow-slip modulated delayed triggering model that we propose can account for the wide range of observed delay times in nature, including the two end-member cases of no delay and no triggering. Triggered slow slip events in nature might provide warning signs of impending earthquakes, underscoring the importance of high-resolution monitoring of active fault zones.

Genetically Engineered Myoblasts for Measuring Nuclear Lamina Stress

The nuclear lamina is a protective shell that controls nuclear stress, and is composed primarily of the protein lamin. Grafting of optical force probes into lamins would provide a real-time readout of nuclear stress, but the expression levels of the chimeric reporter proteins need to be regulated throughout myogenesis. We achieved this by using CRISPR-Cas9 to genetically insert the optical force sensing probe cpstFRET into the nuclear lamins A/C and B1 genes of C2C12 myoblasts, where the cells own genetic regulatory elements control expression. Cell lines, heterozygous for the WT and cpstFRET chimeras of lamin were identified, that formed spontaneously contracting multinucleated myotubes having expression levels of 3:1 of WT:chimeric protein. Isolated nuclei were stretched by swelling via cation depletion, showing an increase in FRET with a force sensitivity of 0.023 and 0.013 FRET units per 1% change in surface area for lamin A/C and B1 respectively. Static and dynamic stresses in vivo caused the greatest magnitude, and most rapid changes, in nuclear stress in myoblasts bound to fibronectin coated surfaces. Substrate stiffness dictates the nuclear stress in flattened myoblasts where the nucleus is in close proximity to the surface. During myogenesis, the nuclear stress is more strongly influenced by the developing contractile machinery. During cell cycle, both lamin subtypes displayed an expected stress decrease during nuclear disassembly at mitosis, but smaller transient stress changes were observed during interphase that differed in timing between type A and B lamins. A surprising property of the angularly sensitive cpstFRET probe was that FRET increased as stress increased. This suggests a length mismatch between heterotypic WT:chimeric lamin pairs causes compression at the cpstFRET insertion site that relaxes with stress. These studies demonstrate the ability to target the insertion of optical force probes into structural proteins.

Postseismic Coulomb stress changes on intra-continental dip-slip faults due to viscoelastic relaxation in the lower crust and lithospheric mantle: insights from 3D finite-element modelling

Earthquakes in the brittle upper crust induce viscoelastic flow in the lower crust and lithospheric mantle, which can persist for decades and lead to significant Coulomb stress changes on receiver faults located in the surrounding of the source fault. As most previous studies calculated the Coulomb stress changes for a specific earthquake in nature, a general investigation of postseismic Coulomb stress changes independent of local geological conditions is still lacking for intra-continental dip-slip faults. Here we use finite-element models with normal and thrust fault arrays, respectively, to show that postseismic viscoelastic flow considerably modifies the original coseismic Coulomb stress patterns through space and time. Depending on the position of the receiver fault relative to the source fault, areas with negative coseismic stress changes may exhibit positive postseismic stress changes and vice versa. The lower the viscosity of the lower crust or lithospheric mantle, the more pronounced are the transient stress changes in the 1st years, with the lowest viscosity having the largest effect on the stress changes. The evolution of postseismic Coulomb stress changes is further controlled by the superposition of transient stress changes caused by viscoelastic relaxation (leading to stress increase or decrease) and the interseismic strain accumulation (leading to a stress increase). Stress changes induced by viscoelastic relaxation can outweigh the interseismic stress increase such that negative Coulomb stress changes can persist for decades. On some faults, postseismic relaxation and interseismic strain accumulation can act in concert to enhance already positive Coulomb stress changes.

Evidence for the release of long‐term tectonic strain stored in continental interiors through intraplate earthquakes

AbstractThe occurrence of large earthquakes in stable continental interiors challenges the applicability of the classical steady state “seismic cycle” model to such regions. Here we shed new light onto this issue using as a case study the cluster of large reverse faulting earthquakes that occurred in Fennoscandia at 11–9 ka, triggered by the removal of the ice load during the final phase of regional deglaciation. We show that these reverse‐faulting earthquakes occurred at a time when the horizontal strain rate field was extensional, which implies that these events did not release horizontal strain that was building up at the time but compressional strain that had been accumulated and stored elastically in the lithosphere over timescales similar to or longer than a glacial cycle. We argue that the tectonically stable continental lithosphere can store elastic strain on long timescales, the release of which may be triggered by rapid, local transient stress changes caused by surface mass redistribution, resulting in the occurrence of intermittent intraplate earthquakes.

Linking megathrust earthquakes to brittle deformation in a fossil accretionary complex

Seismological data from recent subduction earthquakes suggest that megathrust earthquakes induce transient stress changes in the upper plate that shift accretionary wedges into an unstable state. These stress changes have, however, never been linked to geological structures preserved in fossil accretionary complexes. The importance of coseismically induced wedge failure has therefore remained largely elusive. Here we show that brittle faulting and vein formation in the palaeo-accretionary complex of the European Alps record stress changes generated by subduction-related earthquakes. Early veins formed at shallow levels by bedding-parallel shear during coseismic compression of the outer wedge. In contrast, subsequent vein formation occurred by normal faulting and extensional fracturing at deeper levels in response to coseismic extension of the inner wedge. Our study demonstrates how mineral veins can be used to reveal the dynamics of outer and inner wedges, which respond in opposite ways to megathrust earthquakes by compressional and extensional faulting, respectively.

Seismic fatigue failure may have triggered the 2014 Mw7.9 Rat Islands earthquake

AbstractSeismic waves propagating from large earthquakes cause global transient stress changes capable of triggering other earthquakes at great distances. The study of such remote and dynamic triggering phenomena provides a better understanding of the mechanisms that generate earthquakes. I introduce an integrated seismicity model to stochastically evaluate the time intervals of consecutive earthquakes at global scales, making it possible to detect a pair of earthquakes possibly related to each other. I show a Mw7.9 intermediate‐depth earthquake that occurred in the Rat Islands in 2014 is inferred to have been associated with a sequence of distant large (Mw≥6.5) earthquakes originating from the Kermadec Islands. The passage of seismic surface waves from the Kermadec events that produced small stress changes varying within at most 10 Pa at the hypocenter, probably caused a reduction in the fault's strength by cyclic fatigue and eventually triggered its failure during their passage.

Nonstationary ETAS models for nonstandard earthquakes

The conditional intensity function of a point process is a useful tool for generating probability forecasts of earthquakes. The epidemic-type aftershock sequence (ETAS) model is defined by a conditional intensity function, and the corresponding point process is equivalent to a branching process, assuming that an earthquake generates a cluster of offspring earthquakes (triggered earthquakes or so-called aftershocks). Further, the size of the first-generation cluster depends on the magnitude of the triggering (parent) earthquake. The ETAS model provides a good fit to standard earthquake occurrences. However, there are nonstandard earthquake series that appear under transient stress changes caused by aseismic forces such as volcanic magma or fluid intrusions. These events trigger transient nonstandard earthquake swarms, and they are poorly fitted by the stationary ETAS model. In this study, we examine nonstationary extensions of the ETAS model that cover nonstandard cases. These models allow the parameters to be time-dependent and can be estimated by the empirical Bayes method. The best model is selected among the competing models to provide the inversion solutions of nonstationary changes. To address issues of the uniqueness and robustness of the inversion procedure, this method is demonstrated on an inland swarm activity induced by the 2011 Tohoku-Oki, Japan earthquake of magnitude 9.0.

The Mw 8.6 Indian Ocean Earthquake on 11 April 2012: Coseismic Displacement, Coulomb Stress Change and Aftershocks Pattern

Abstract The Mw 8.6 Indian Ocean earthquake occurred on April 11, 2012 near the NW junction of three plates viz. Indian, Australian and Sunda plate, which caused widespread coseismic displacements and Coulomb stress changes. We analyzed the GPS data from three IGS sites PBRI, NTUS & COCO and computed the coseismic horizontal displacements. In order to have in-depth understanding of the physics of earthquake processes and probabilistic hazard, we estimated the coseismic displacements and associated Coulomb stress changes from two rectangular parallel fault geometries, constrained by Global Positioning System (GPS) derived coseismic displacements. The Coulomb stress changes following the earthquake found to be in the range of 5 to -4 bar with maximum displacement of ∼11 m near the epicenter. We find that most of the aftershocks occurred in the areas of increased Coulomb stress and concentrated in three clusters. The temporal variation of the aftershocks, not conformed to modified Omori’s law, speculating poroelastic processes. It is also ascertained that the spatio-temporal transient stress changes may promote the occurrence of the subsequent earthquakes and enhance the seismic risk in the region.

Implications of recent asperity failures and aseismic creep for time-dependent earthquake hazard on the Hayward fault

The probability of large seismic events on a particular fault segment may vary due to external stress changes imparted by nearby deformation events, including other earthquakes and aseismic processes, such as fault creep and postseismic relaxation. The Hayward fault (HF), undergoing both seismic and aseismic fault slip, provides a unique opportunity to study the mutual relation of seismic and aseismic processes on a fault system. We use surface deformation data obtained from InSAR (interferometric synthetic aperture radar), creepmeters and alinement arrays, together with constraints provided by repeating earthquakes to investigate the kinematics of fault creep on the northern HF and its relation to two seismic clusters (Mw≤4.1) in October 2011 and March 2012, and an Mw 4.2 event in July 2007. Recurrences of nearby repeating earthquakes show that these episodes involved both seismic and aseismic slip. We model the stress changes due to fault creep and the recent seismic activity on the locked central asperity of the HF, which is believed to be the rupture zone of past and future M~7 earthquakes. The results show that the shallow fault creep stresses the major locked central patch at an average rate of 0.001–0.003MPa/yr, in addition to background stressing at 0.01–0.015MPa/yr. Given the time-dependent nature of the creep, occasional deviations from this stressing rate occur. We find that the 2011 seismic cluster occurred in areas on the fault that are stressed up to 0.01MPa/yr due to aseismic slip on the surrounding segments, suggesting that the occurrence of these events was encouraged by the fault creep. Changes in the probability of major earthquakes can be estimated from the imparted stress from the recent earthquakes and associated fault creep transients. We estimate that the 1-day probability of a large event on the HF only increased by up to 0.18% and 0.05% due to the static stress increase and stressing rate change by the 2011 and 2012 clusters. For the July 2007 south Oakland event (Mw 4.2) the estimated increase of short-term probabilities is 50%, highlighting the importance of short-term probability changes due to transient stress changes.

Space-time heterogeneity in aftershock activity

For a number of aftershock sequences in and around Japan, we examine detrended space—time coordinates after fitting the Omori–Utsu occurrence rate to each aftershock sequence. The case studies in conjunction with the fault locations and orientations of the main shocks and focal large aftershocks indicate that the region of deficit and surplus in the aftershock activity well corresponds to the decreased and increased region of Coulomb failure stress, respectively, caused by various aseismic slips. We illustrate the relation between the transient stress changes and the anomalous aftershock activity in a local subregion by six scenarios derived from the rate and state dependent friction law of Dietrich.

Non-volcanic tremor resulting from the combined effect of Earth tides and slow slip events

Swarms of non-volcanic tremor in southeastern Japan are associated with slow slip events and tend to occur with a periodicity of 12 or 24 h. This periodicity can be reproduced by a combination of stresses due to Earth tides and transient stress changes caused by slow slip events. Non-volcanic tremors may therefore be useful for understanding stress relaxation at the subduction-zone interface. Slow slip events1 are accompanied by swarms of non-volcanic tremor2,3 along the subduction zone of the Philippine Sea plate in southwest Japan: the swarms often occur with a periodicity of about 12 or 24 h (refs 4, 5). These episodic events are considered to be a manifestation of stress relaxation at the subducting plate interface1,6,7. Here, we analyse seismic data to record the locations and durations of non-volcanic tremor swarms that occurred in May 2005 and February 2006. We evaluate the magnitude of stress changes produced by slow slip events as well as the effective normal stress on the plate interface where slow slip events occur. We find that the observed periodicity in tremor occurrence originates from a combined effect of the periodic stress due to Earth tides and the transient stress due to slow slip events. Our calculations show that non-volcanic tremor is sensitive to stress change. This phenomenon can therefore be effective in monitoring the process of stress relaxation at subducting plate interfaces.

Earthquake Time Cluster in North-East India During February to April 1988

During the time interval of 3 February to 20 April 1988 four independent main shocks occurred in North-East (NE) India: 03/02/1988, M = 5.5; 06/20/1988, M = 5.8; 15/04/1988, M = 6.2 and 20/04/1988, M = 5.8. The seismicity rate within this 78 day interval is increased by a factor of 15 and 6 with respect to the mean, long term seismicity for M ≥ 5.5 and M ≥ 6.1, respectively. In terms of probability, it has been found out that the probability of observing by chance four events of M ≥ 5.5 or one events of M ≥ 6.1 in NE-India is equal to only 0.4243 and 0.3680, respectively. These results imply that the observed seismicity has a non-random time clustering. Similar earthquake time clusters were identified to have occurred in NE-India in 1930 and 1951. A triggering mechanism has been proposed to interpret the earthquake clustering: the first event of the earthquake sequence produces transient stress changes that cause an acceleration to the static stress loading, and then to seismic failure, to remote highly pre stressed regions.

An unusual earthquake time cluster in the Greek mainland during May–June 1995

During the time interval of 4 May–15 June 1995 four independent mainshocks occurred in the Greek mainland: 4/5/95, M s = 5.5; 9/5/95, M s = 5.2; 13/5/95, M s =6.6; 15/6/95, M s = 6.1. The seismicity rate within this 43-day interval is increased by a factor of 34 and 71 with respect to the mean, long-term seismicity for M s ≥ 5.2 and M s ≥ 6.1, respectively. In terms of probability, it has been found out that the probability of observing by chance four events of M s ≥ 5.2 or two events of M s ≥ 6.1 in the Greek mainland is equal to only 7.12 × 10 −6 and 3.82 × 10 −4, respectively. These results imply that the observed seismicity has been a non-random time clustering. Similar earthquake time clusters were identified to have occurred in the Greek mainland in 1911 and 1931. A triggering mechanism has been modeled to interprete the earthquake clustering: the first event of the earthquake sequence produces transient stress changes that cause an acceleration to the stress loading, and then to seismic failure, to remote highly prestressed regions.

Dynamic stress variations due to shear faults in a plane-layered medium

SUMMARY A complete set of expressions is presented for the computation of elastic dynamic stress in plane-layered media. We use a discrete-wavenumber reflectivity method to compute the stress field radiated by arbitrary moment-tensor sources. The expressions derived here represent an interesting tool for both-the observational and theoretical analysis of dynamic stress changes associated with earthquake phenomena. Dynamic stress changes associated with a strike-slip fault having unilateral rupture are shown. This modelling, which is similar to the 1992 Landers California earthquake, illustrates the effects of distance, directivity and depth on transient stress changes.