scholarly journals Sequences of seismic and aseismic slip on bimaterial faults show dominant rupture asymmetry and potential for elevated seismic hazard

2021 ◽  
Author(s):  
Mohamed Abdelmeguid ◽  
Ahmed Elbanna
Keyword(s):  
Seismic Hazard ◽  
Normal Stress ◽  
Nucleation Site ◽  
Rupture Propagation ◽  
Aseismic Slip ◽  
Earthquake Physics ◽  
Slip Rates ◽  
Seismicity Pattern ◽  
Sequence Of Events ◽  
Material Contrast

We perform numerical simulations of sequences of earthquake and aseismic slip on planar rate and state faults separating dissimilar material within the 2-D plane strain approximation. We resolve all stages of the earthquake cycle from aseismic slip to fast ruptures while incorporating full inertia effects during seismic event propagation. We show that bimaterial coupling results in favorable nucleation site and subsequent asymmetric rupture propagation. We demonstrate that increasing the material contrast enhances this asymmetry leading to higher slip rates and normal stress drops in the preferred rupture propagation direction. The normal stress drop, induced by the bimaterial effect, leads to strong dynamic weakening of the fault and may destabilize the creeping region on a heterogeneous rate and state fault, resulting in extended rupture propagation. Such rupture penetration into creeping patches may lead to more frequent opening of earthquake gates, causing increased seismic hazard. Furthermore, bimaterial coupling may lead to irregular seismicity pattern in terms of event length, peak slip rates,and hypocenter location, depending on the properties of the creeping patches bordering the seismogenically active part of the fault . Our results highlight robust characteristics of bimaterial interfaces that persist over long sequence of events and suggest the need for further exploration of the role of material contrast in earthquake physics and models of seismic hazard.

Challenges and Opportunities in Turning Large U.S. Archives of Analog Seismograms into a Modern Usable Resource

2020 ◽  
Vol 91 (3) ◽  
pp. 1531-1541
Author(s):  
Paul G. Richards ◽  
Margaret Hellweg
Keyword(s):  
Seismic Hazard ◽  
Scientific Information ◽  
Practical Experience ◽  
Earthquake Physics ◽  
Timing Information ◽  
Earthquake Sources ◽  
Challenges And Opportunities ◽  
Test Ban ◽  
Level Of Effort

Abstract Quantitative seismology is based firmly on the analysis of actual ground motions, and the transition to digital recording in the 1980s enabled sophisticated new capabilities to extract useful results from waveforms. With some effort, these tools can also be applied to analog records. Focusing on assets available within U.S. institutions, we review the necessary steps and the challenges in enabling “data rescue”—that is, preserving the scientific information latent in large analog seismogram archives and making it usable. They include: determining what assets are available (the analog seismogram archives held by various institutions, with associated metadata on instrument responses, station locations, and timing information); developing a consensus on the top level of a triage process (which analog records most definitely should be rescued?); deciding the level of quality needed in copying original seismograms to media suitable for digitizing; assessing the relative merits of scanning and digitizing; and, the need for a community service in distributing scans and digital records, as they accumulate. The necessary level of effort can benefit from practical experience. For example, specific studies have used digitized versions of analog recordings to model earthquake sources and assess seismic hazard. Other studies have used them to gain experience with nuclear explosion signals recorded at regional distances, noting that regional signals enable explosions to be monitored down to levels much lower than those attainable teleseismically. The opportunities presented by large archives of analog seismograms include the insights they present to current and future seismologists studying earthquakes and explosions, into the practical areas of assessing seismic hazard, monitoring for test ban compliance down to low explosion yields—and prompt characterization of actual explosions should they occur, as well the traditional academic pursuit of a better understanding of earthquake physics.

scholarly journals Tectonic Geomorphology and Paleoseismology of the Sharkhai fault: a new source of seismic hazard for Ulaanbaatar (Mongolia)

2021 ◽  
Author(s):  
Abeer Al-Ashkar ◽  
Antoine Schlupp ◽  
Matthieu Ferry ◽  
Ulziibat Munkhuu
Keyword(s):  
Seismic Hazard ◽  
Scaling Laws ◽  
Active Faults ◽  
Seismic Hazard Assessment ◽  
Capital City ◽  
Tectonic Geomorphology ◽  
Time Interval ◽  
Coseismic Slip ◽  
Slip Rates ◽  
Large Earthquakes

Abstract. We present new constraints from tectonic geomorphology and paleoseismology along the newly discovered Sharkhai fault near the capital city of Mongolia. Detailed observations from high resolution Pleiades satellite images and field investigations allowed us to map the fault in detail, describe its geometry and segmentation, characterize its kinematics, and document its recent activity and seismic behavior (cumulative displacements and paleoseismicity). The Sharkhai fault displays a surface length of ~40 km with a slightly arcuate geometry, and a strike ranging from N42° E to N72° E. It affects numerous drainages that show left-lateral cumulative displacements reaching 57 m. Paleoseismic investigations document the faulting and deposition record for the last ~3000 yr and reveal that the penultimate earthquake (PE) occurred between 1515 ± 90 BC and 945 ± 110 BC and the most recent event (MRE) occurred after 860 ± 85 AD. The resulting time interval of 2080 ± 470 years is the first constraint on the Sharkhai fault for large earthquakes. On the basis of our mapping of the surface rupture and the resulting segmentation analysis, we propose two possible scenarios for large earthquakes with likely magnitudes between 6.4 ± 0.2 and 7.1 ± 0.2. Furthermore, we apply scaling laws to infer coseismic slip values and derive preliminary estimates of long-term slip rates between 0.2 ± 0.2 and 1.0 ± 0.5 mm/y. Finally, we propose that these original observations and results from a newly discovered fault should be taken into account for the seismic hazard assessment for the city of Ulaanbaatar and help build a comprehensive model of active faults in that region.

scholarly journals Integrating faults and past earthquakes into a probabilistic seismic hazard model for peninsular Italy

2017 ◽  
Vol 17 (11) ◽  
pp. 2017-2039 ◽  
Author(s):  
Alessandro Valentini ◽  
Francesco Visini ◽  
Bruno Pace
Keyword(s):  
Seismic Hazard ◽  
Seismic Activity ◽  
Grid Point ◽  
Active Faults ◽  
Gaussian Model ◽  
Probabilistic Seismic Hazard ◽  
Maximum Magnitude ◽  
Slip Rates ◽  
Earthquake Sources ◽  
The Impact

Abstract. Italy is one of the most seismically active countries in Europe. Moderate to strong earthquakes, with magnitudes of up to ∼ 7, have been historically recorded for many active faults. Currently, probabilistic seismic hazard assessments in Italy are mainly based on area source models, in which seismicity is modelled using a number of seismotectonic zones and the occurrence of earthquakes is assumed uniform. However, in the past decade, efforts have increasingly been directed towards using fault sources in seismic hazard models to obtain more detailed and potentially more realistic patterns of ground motion. In our model, we used two categories of earthquake sources. The first involves active faults, and using geological slip rates to quantify the seismic activity rate. We produced an inventory of all fault sources with details of their geometric, kinematic, and energetic properties. The associated parameters were used to compute the total seismic moment rate of each fault. We evaluated the magnitude–frequency distribution (MFD) of each fault source using two models: a characteristic Gaussian model centred at the maximum magnitude and a truncated Gutenberg–Richter model. The second earthquake source category involves grid-point seismicity, with a fixed-radius smoothed approach and a historical catalogue were used to evaluate seismic activity. Under the assumption that deformation is concentrated along faults, we combined the MFD derived from the geometry and slip rates of active faults with the MFD from the spatially smoothed earthquake sources and assumed that the smoothed seismic activity in the vicinity of an active fault gradually decreases by a fault-size-driven factor. Additionally, we computed horizontal peak ground acceleration (PGA) maps for return periods of 475 and 2475 years. Although the ranges and gross spatial distributions of the expected accelerations obtained here are comparable to those obtained through methods involving seismic catalogues and classical zonation models, the spatial pattern of the hazard maps obtained with our model is far more detailed. Our model is characterized by areas that are more hazardous and that correspond to mapped active faults, while previous models yield expected accelerations that are almost uniformly distributed across large regions. In addition, we conducted sensitivity tests to determine the impact on the hazard results of the earthquake rates derived from two MFD models for faults and to determine the relative contributions of faults versus distributed seismic activity. We believe that our model represents advancements in terms of the input data (quantity and quality) and methodology used in the field of fault-based regional seismic hazard modelling in Italy.

scholarly journals Bayesian earthquake dating and seismic hazard assessment using chlorine-36 measurements (BED v1)

2018 ◽  
Vol 11 (11) ◽  
pp. 4383-4397 ◽  
Author(s):  
Joakim Beck ◽  
Sören Wolfers ◽  
Gerald P. Roberts
Keyword(s):  
Inverse Problem ◽  
Seismic Hazard ◽  
Hazard Assessment ◽  
Ad Hoc ◽  
Seismic Hazard Assessment ◽  
Fault Scarp ◽  
Physical Models ◽  
Monte Carlo Algorithm ◽  
Slip Rates ◽  
Chlorine 36

Abstract. Over the past 20 years, analyzing the abundance of the isotope chlorine-36 (36Cl) has emerged as a popular tool for geologic dating. In particular, it has been observed that 36Cl measurements along a fault plane can be used to study the timings of past ground displacements during earthquakes, which in turn can be used to improve existing seismic hazard assessment. This approach requires accurate simulations of 36Cl accumulation for a set of fault-scarp rock samples, which are progressively exhumed during earthquakes, in order to infer displacement histories from 36Cl measurements. While the physical models underlying such simulations have continuously been improved, the inverse problem of recovering displacement histories from 36Cl measurements is still mostly solved on an ad hoc basis. The current work resolves this situation by providing a MATLAB implementation of a fast, automatic, and flexible Bayesian Markov-chain Monte Carlo algorithm for the inverse problem, and provides a validation of the 36Cl approach to inference of earthquakes from the demise of the Last Glacial Maximum until present. To demonstrate its performance, we apply our algorithm to a synthetic case to verify identifiability, and to the Fiamignano and Frattura faults in the Italian Apennines in order to infer their earthquake displacement histories and to provide seismic hazard assessments. The results suggest high variability in slip rates for both faults, and large displacements on the Fiamignano fault at times when the Colosseum and other ancient buildings in Rome were damaged.

scholarly journals Fault System-Based Probabilistic Seismic Hazard Assessment of a Moderate Seismicity Region: The Eastern Betics Shear Zone (SE Spain)

2020 ◽  
Vol 8 ◽  
Author(s):  
Octavi Gómez-Novell ◽  
Julián García-Mayordomo ◽  
María Ortuño ◽  
Eulàlia Masana ◽  
Thomas Chartier
Keyword(s):  
Seismic Hazard ◽  
Return Period ◽  
Fault System ◽  
Probabilistic Seismic Hazard ◽  
Se Spain ◽  
Slip Rates ◽  
Area Source ◽  
Moderate Seismicity ◽  
Background Seismicity ◽  
Hazard Levels

Including faults as seismogenic sources in probabilistic seismic hazard assessments (PSHA) has turned into a common practice as knowledge of active faults is improving. Moreover, the occurrence of earthquakes in multi-fault ruptures has evidenced the need to understand faults as interacting systems rather than independent sources. We present a PSHA for the Southeastern Spain obtained by including the faults of a moderate seismicity region, the Eastern Betics Shear Zone (EBSZ) in SE Spain, as the main seismogenic sources in two separate source models, one considering background seismicity. In contrast with previous studies in Spain, earthquake occurrence of the EBSZ system is modeled considering different hypotheses of multi-fault ruptures at the whole fault system scale and weighted in a logic tree. We compare the hazard levels with those from an area source PSHA and a previous fault-based approach. The results show a clear control of the EBSZ faults in the seismic hazard for all return periods, increasing drastically the hazard levels in the regions close to the fault traces and influencing up to 20 km farther with respect to the area source PSHA. The seismic hazard is dependent on the fault slip rates as peak ground accelerations and territorial extension of the fault influence appear higher around the Alhama de Murcia and Carboneras faults, while lower slip rate faults (Palomares Fault) show minor contribution to the hazard. For the return period of 475 years and near-fault locations, our models are more consistent with the ground motion values reached in the 2011 Mw 5.2 Lorca event than the building code or national seismic hazard map, which suggest that our fault system-based model performs more accurate estimations for this return period. Fault data, mainly slip rates, and its uncertainties have a clear impact on the seismic hazard and, for some faults, the lack of detailed paleoseismic studies can compromise the reliability of the hazard estimations. This, together with epistemic uncertainties concerning the background seismicity, are key discussion points in the present study, having an impact on further research and aiming to serve as a case example for other low-to-moderate seismicity regions worldwide.

scholarly journals Updating seismic hazard models for Kuwait

2021 ◽  
Author(s):  
Abd el-aziz Khairy Abd el-aal ◽  
Shaimaa Ismail Mostafa ◽  
Abdullah Al-Enezi ◽  
Farah Al-Jeri ◽  
Ammar Al-Sayegh
Keyword(s):  
Seismic Hazard ◽  
Seismic Risk ◽  
Epistemic Uncertainty ◽  
Probabilistic Approach ◽  
Tall Buildings ◽  
Seismic Source ◽  
Hazard Maps ◽  
Seismicity Pattern ◽  
Uniform Hazard Spectrum ◽  
The State Of Kuwait

Abstract The valuable results from this research are the first and essential step for assessing seismic risk in Kuwait. The increase in the urban development and construction of tall buildings and skyscrapers in Kuwait necessitated an estimate of the seismic risk for creating a unified seismic code for Kuwait. This research comes to make the necessarily step by assessing the seismic hazard and deaggregation in the State of Kuwait. For this purpose, the historical and instrumental seismic catalogs of Kuwait and the active Zagros Seismic Belt were primarily compiled, unifying the magnitudes, removing unnecessary earthquakes (seismicity declustering) and considering the completeness of the catalogs. Multi-seismotectonic models for Kuwait region incorporate earthquake focal mechanisms, seismicity pattern, and structural geological situation have been created to reduce epistemic uncertainty. The recurrence parameters as well as the maximum expected earthquake from each seismic source were fundamentally estimated. Appropriate ground motion attenuation relation within a logic tree formulation was mainly used in creating hazard maps. A state-of-the-art probabilistic approach is used herein to produce hazard maps at return periods of 75, 475, 975 and 2475 years (equivalent to 50%, 10%, 5% and 2%, respectively, probability of exceedance in 50 years) at periods of PGA, 0.1, 1 and 4 seconds. The computations of hazard maps were constructed using spacing grid of 0.2° × 0.2° all over the Kuwait area. Uniform hazard spectrum and deaggregation charts have been adopted for all six governorates of Kuwait. These results with vulnerability index are the main components for estimating the seismic risk of Kuwait.

scholarly journals A systems-based approach to parameterise seismic hazard in regions with little historical or instrumental seismicity: The South Malawi Active Fault Database

2020 ◽  
Author(s):  
Jack N. Williams ◽  
Hassan Mdala ◽  
Åke Fagereng ◽  
Luke N. J. Wedmore ◽  
Juliet Biggs ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Active Fault ◽  
Slip Rate ◽  
Fault Slip ◽  
Slip Rates ◽  
Scaling Relationships ◽  
Regional Strain ◽  
Earthquake Scaling ◽  
Recurrence Intervals ◽  
Fault Slip Rate

Abstract. Seismic hazard is frequently characterised using instrumental seismic records. However, in regions where the instrumental record is short relative to earthquake repeat times, extrapolating it to estimate seismic hazard can misrepresent the probable location, magnitude, and frequency of future large earthquakes. Although paleoseismology can address this challenge, this approach requires certain geomorphic settings and carries large inherent uncertainties. Here, we outline how fault slip rates and recurrence intervals can be estimated through an approach that combines fault geometry, earthquake-scaling relationships, geodetically derived regional strain rates, and geological constraints of regional strain distribution. We then apply this approach to the southern Malawi Rift where, although no on-fault slip rate measurements exist, there are theoretical and observational constraints on how strain is distributed between border and intrabasinal faults. This has led to the development of the South Malawi Active Fault Database (SMAFD), the first database of its kind in the East African Rift System (EARS) and designed so that the outputs can be easily incorporated into Probabilistic Seismic Hazard Analysis. We estimate earthquake magnitudes of MW 5.4–7.2 for individual fault sections in the SMAFD, and MW 6.0–7.8 for whole fault ruptures. These potentially high magnitudes for continental normal faults reflect southern Malawi's 11–140 km long faults and thick (30–35 km) seismogenic crust. However, low slip rates (intermediate estimates 0.05–0.8 mm/yr) imply long recurrence intervals between events: 102–105 years for border faults and 103–106 years for intrabasinal faults. Sensitivity analysis indicates that the large range of these estimates can be reduced most significantly from an improved understanding of the rate and partitioning of rift-extension in southern Malawi, earthquake scaling relationships, and earthquake rupture scenarios. Hence these are critical areas for future research. The SMAFD provides a framework for using geological and geodetic information to characterize seismic hazard in low strain rate settings with few on-fault slip rate measurements, and could be adapted for use elsewhere in the EARS or globally.

Sign in / Sign up

Export Citation Format

Share Document