Foreshocks of the 2018 ML 4.0 Shimian Earthquake in the Anninghe Fault and Its Implications for Earthquake Nucleation

2021 ◽  
Author(s):  
Tian Feng ◽  
Jianping Wu ◽  
Lihua Fang ◽  
Xiangyun Guo ◽  
Yan Cai ◽  
...  
Keyword(s):  
Fault Plane ◽  
Intraplate Earthquakes ◽  
Earthquake Detection ◽  
Earthquake Nucleation ◽  
Stress Triggering ◽  
Low Incidence ◽  
Partial Overlap ◽  
Occurrence Mechanism ◽  
Large Earthquakes ◽  
Anninghe Fault

Abstract Foreshock activity sometimes precedes large earthquakes, but how foreshocks relate to mainshock nucleation is still unclear with limited case studies existing. One way to further the understanding of the foreshock occurrence mechanism is to maximize the resolution of the foreshock characteristics by waveform-based earthquake detection and location. Here, we apply the match and locate method to scan continuous waveforms 30 days before and 44 days after the 2018 ML 4.0 Shimian earthquake in Sichuan, China, and obtain approximately three times more events than reported in a local catalog. The augmented seismicity suggests the existence of a blind small strike-slip fault deep in the east of the Anninghe fault. Forty-one foreshocks of magnitude ranging from ML−0.7 to 3.4 occurred within 4 hr before the mainshock and did not show an accelerating pattern leading up to the mainshock. Focal mechanisms are consistent between the mainshock and foreshocks, implying that the mainshock and foreshock hypocenters are located on the same fault plane. The high-precision relative locations reveal that most of the foreshocks rupture adjacent source patches along the fault plane, with little or partial overlap, which is consistent with cascade stress triggering from foreshocks to foreshocks to the mainshock. Our research is one of the few to focus on the foreshock sequence of moderate mainshocks and provides a new case for studying the mechanism of foreshocks of intraplate earthquakes with a low incidence of foreshocks.

Modeling Earthquakes Using Fractal Circular Patch Models with Lessons from the 2011 Tohoku-Oki Earthquake

2014 ◽  
Vol 9 (3) ◽  
pp. 264-271 ◽  
Author(s):  
Satoshi Ide ◽  
◽  
Hideo Aochi ◽  
Keyword(s):  
Fault Plane ◽  
Large Earthquake ◽  
Rupture Process ◽  
Fault System ◽  
External Loading ◽  
Dynamic Rupture ◽  
Consistent Model ◽  
Wide Scale ◽  
Seismicity Catalog ◽  
Large Earthquakes

Earthquakes occur in a complex hierarchical fault system, meaning that a realistic mechanically-consistent model is required to describe heterogeneity simply and over a wide scale. We developed a simple conceptual mechanical model using fractal circular patches associated with fracture energy on a fault plane. This model explains the complexity and scaling relation in the dynamic rupture process. We also show that such a fractal patch model is useful in simulating longterm seismicity in a hierarchal fault system by using external loading. In these studies, an earthquake of any magnitude appears as a completely random cascade growing from a small patch to larger patches. This model is thus potentially useful as a benchmarking scenario for evaluating probabilistic gain in probabilistic earthquake forecasts. The model is applied to the real case of the 2011 Tohoku-Oki earthquake based on prior information from a seismicity catalog to reproduce the complex rupture process of this very large earthquake and its resulting ground motion. Provided that a high-quality seismicity catalog is available for other regions, similar approach using this conceptual model may provide scenarios for other potential large earthquakes.

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

2021 ◽  
Author(s):  
Yu Jiang ◽  
Pablo González
Keyword(s):  
Fault Plane ◽  
Surface Displacement ◽  
Fault Slip ◽  
Geodetic Data ◽  
Source Regions ◽  
Seismogenic Source ◽  
Earthquake Nucleation ◽  
Slip Area ◽  
Earthquake Sequences

<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>

Earthquake fault plane solutions near Vancouver Island

1979 ◽  
Vol 16 (3) ◽  
pp. 523-531 ◽  
Author(s):  
Garry C. Rogers
Keyword(s):  
Fault Plane ◽  
Vancouver Island ◽  
Nodal Solutions ◽  
Island Region ◽  
Fault Plane Solutions ◽  
Principal Compressive Stress ◽  
Predominant Type ◽  
Shallow Earthquakes ◽  
Aftershock Sequences ◽  
Large Earthquakes

P nodal solutions for six earthquakes in the Vancouver Island region are consistent with a north–south orientation for the principal compressive stress. The predominant type of faulting is strike slip, either dextral slip on northwest striking faults or sinistral slip on northeast striking faults. The few aftershock sequences that can be documented for shallow earthquakes greater than magnitude 5 all contain very few aftershocks, which are small in size. This may indicate that higher than average stress drop is characteristic of large earthquakes in the Vancouver Island region.

Systematic Investigation of Dynamic Earthquake Triggering in Japan

2021 ◽  
Author(s):  
Bogdan Enescu ◽  
Yuki Takeda
Keyword(s):  
Systematic Investigation ◽  
Earthquake Triggering ◽  
Significance Level ◽  
Dynamic Triggering ◽  
Stress Triggering ◽  
Remote Triggering ◽  
Pressure Changes ◽  
Large Earthquakes ◽  
Swarm Earthquakes ◽  
Triggering Threshold

<p><strong>Introduction. </strong>Previous studies (e.g., Harrington and Brodsky, 2006) documented a relative scarcity of remote triggering in Japan, compared to other seismic regions. For example, in California, dynamic triggering is reported to occur at levels of stress as small as 0.1 kPa, while in Japan it was reported that levels of 30 kPa or more are required to trigger detectable events (van der Elst and Brodsky, 2010). However, the threshold dynamic triggering level following the 2016 M7.3 Kumamoto earthquake was of just a few kPa (Enescu et al., 2016). Enescu et al. (2016) proposed that one of the possibilities to explain this observation is a change of stress triggering threshold that may have taken place after the 2011 M9.0 Tohoku-Oki earthquake.</p><p><strong>Motivation.</strong> Given the above observations, this study investigates 1) the occurrence of dynamically triggered earthquakes in Japan after some large earthquakes from 2004, and 2) whether the threshold of dynamic triggering may have changed due to the 2011 Tohoku-Oki earthquake and why this threshold might have changed.</p><p><strong>Analysis and Results.</strong> First, we investigated dynamic triggering throughout Japan, following some large earthquakes occurred after 2004. As a result, the  threshold appears to decrease following the 2011 Tohoku-Oki earthquake, however the number of earthquakes we have investigated was relatively small, so we could not draw statistically significant conclusions. In the second part of the study, we have focused on a few specific areas within Japan to systematically investigate dynamic triggering, which reduced significantly the computational costs. Thus, we focused on some areas in Tohoku and Hida, where swarm earthquakes occurred after the 2011 Tohoku-Oki earthquake. As a result, the change of the triggering level in an area close to the Yamagata-Fukushima border is considered to be statically significant at a 5% significance level. In other regions, the significance at a 5% level could not be established, however a decrease of this threshold is apparent, except for one region. We speculate that changes in the stress triggering threshold levels might be related to pore pressure changes in the crust following the 2011 Tohoku-Oki earthquake.</p>

scholarly journals Preliminary re-evaluation of probabilistic seismic hazard assessment in Chile: from Arica to Taitao Peninsula

2009 ◽  
Vol 22 ◽  
pp. 147-153 ◽  
Author(s):  
F. Leyton ◽  
S. Ruiz ◽  
S. A. Sepúlveda
Keyword(s):  
Seismic Hazard ◽  
Hazard Assessment ◽  
Seismic Hazard Assessment ◽  
Probabilistic Seismic Hazard Assessment ◽  
Probabilistic Seismic Hazard ◽  
Intraplate Earthquakes ◽  
Ground Acceleration ◽  
The Andes ◽  
Available Information ◽  
Large Earthquakes

Abstract. Chile is one of the most seismically active countries in the world; indeed, having witnessed very large earthquakes associated with high horizontal peak ground accelerations, the use of probabilistic hazard assessment is an important tool in any decision-making. In the present study, we review all the available information to improve the estimation of the probabilistic seismic hazard caused by two main sources: shallow interplate, thrust earthquakes and intermediate depth, intraplate earthquakes. Using previously defined seismic zones, we compute Gutenberg-Richter laws and, along with appropriate attenuation laws, revaluate the probabilistic seismic hazard assessments in Chile. We obtain expected horizontal peak ground acceleration with a 10% of probability of being exceeded in 50 years, reaching from 0.6 g up 1.0 g in the coast and between 0.4 g and 0.6 g towards the Andes Mountains, with larger values in Northern part of the country. The present study improves our knowledge of geological hazards in Chile, enabling the mitigation of important human and material losses due to large earthquakes in the future.

The 2017 November 12 Mw 7.3 Sarpol-Zahab (Iran-Iraq border region) earthquake: source model, aftershock sequence and earthquakes triggering

2020 ◽  
Author(s):  
Mohammadreza Jamalreyhani ◽  
Mehdi Rezapour ◽  
Simone Cesca ◽  
Sebastian Heimann ◽  
Hannes Vasyura-Bathke ◽  
...  
Keyword(s):  
Fault Plane ◽  
Joint Inversion ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Fault Slip ◽  
Earthquake Source ◽  
Border Region ◽  
Model Parameters ◽  
Fault Geometry ◽  
Large Earthquakes

<p>The Mw 7.3 Sarpol-Zahab earthquake occurred on 12 November 2017 in the Lurestan arc of the Zagros Simply Folded Belt (ZSFB). It is estimated that 600 people were killed and 8000 were injured in this earthquake. This earthquake has been the largest instrumentally recorded earthquake in the ZSFB and its moment, as well as its mechanism, were unexpected. We present an earthquake source study on the Mw 7.3 Sarpol-Zahab earthquake, two large following earthquakes in the region in 2018 and their corresponding aftershock sequences to gain insight of seismotectonic of the Lurestan arc fold-thrust belt.</p><p>In this study, we complement previous studies on this earthquake, by non-linear probabilistic optimization of joined geodetic and seismic data using a new, efficient Bayesian bootstrap-based optimization scheme to infer the finite fault geometry and fault slip together with meaningful uncertainty estimates of the model parameters. Our optimization is based on the modeling of ascending and descending Sentinel-1 satellite data, seismological waveform from global seismic networks and the strong motion network of Iran. The posterior mean model of the Sarpol-Zahab earthquake shows that the causative fault plane is centered at is 14±2 km depth and has a low dip angle of 17°±2° and a strike of 350°±10°. The rake angle of 144°±4° points to an oblique thrust mechanism. The rupture area of the uniform-slip, rectangular model is 40±2 km long and 16±2 km width and shows 4.0±0.5 m fault slip, which results in a magnitude estimate of Mw 7.3±0.1.</p><p>Later, in August and November 2018, two large earthquakes with Mw 6.0 and Mw 6.4 occurred about 40 km east and 60 km south of the Sarpol-Zahab epicenter, respectively. These earthquakes could have been triggered by the 2017 Sarpol-Zahab earthquake. We apply the same joint inversion modeling to derive the corresponding fault plane solutions. We found strike-slip mechanisms for both events but centroid depths at 10±2 km and 16±2 km for Mw 6.0 and Mw 6.4, respectively.</p><p>The 2017 Sarpol-Zahab earthquake and the following studied 2018 earthquakes were followed by a sustained aftershock sequence, with more than 133 aftershocks exceeding Ml 4.0 until December 30, 2019. We rely on the local and regional seismic broad-band stations of Iran and Iraq permanent networks to estimate full-waveform moment tensor solutions of 70 aftershocks down to Ml 4. Most of these aftershocks have shallow centroid depths between 5 and 12 km, so that they occurred in the uppermost part of the basement and/or in the lower sedimentary cover, which is ~8 km thick in this area.</p><p>Our results suggest that the Sarpol-Zahab earthquakes activated low-angle thrust faults and shallower strike-slip structures, highlighting that both thin- and thick-skin deformation take place in the fold-thrust belts in the Lurestan arc of the Zagros. Such information on the deformation characteristics is important for the hazard and risk assessment of future large earthquakes in this region.<br>Additionally, we demonstrate how the joint inversion of different geophysical data can help to better resolve the fault geometry and the earthquake source parameters.</p>

Sign in / Sign up

Export Citation Format

Share Document