Active Fault Data Research Articles

Geologic and geodetic constraints on the magnitude and frequency of earthquakes along Malawi's active faults: the Malawi Seismogenic Source Model (MSSM)

Abstract. Active fault data are commonly used in seismic hazard assessments, but there are challenges in deriving the slip rate, geometry, and frequency of earthquakes along active faults. Herein, we present the open-access geospatial Malawi Seismogenic Source Model (MSSM; https://doi.org/10.5281/zenodo.5599616), which describes the seismogenic properties of faults that formed during ongoing east African rifting in Malawi. We first use empirically derived constraints to geometrically classify active faults into section, fault, and multifault seismogenic sources. For sources in the North Basin of Lake Malawi, slip rates can be derived from the vertical offset of a seismic reflector that dated lake cores indicate is 75 ka. Elsewhere, slip rates are constrained from advancing a systems-based approach that partitions geodetically derived rift extension rates in Malawi between seismogenic sources using a priori constraints on a regional strain distribution and a hanging wall flexural extension in magma-poor continental rifts. Slip rates are then combined with source geometry and empirical scaling relationships to estimate earthquake magnitudes and recurrence intervals, and their uncertainty is described from the variability in logic tree outcomes used in these calculations. Sources in the MSSM are 5–269 km long, which implies that large-magnitude (Mw 7–8) earthquakes may occur in Malawi. However, low slip rates (0.05–2 mm yr−1) mean that the frequency of such events will be low (recurrence intervals of ∼103–104 years). We also find that, for 9 out of 11 faults in Lake Malawi's North Basin, differences in the slip rates, when estimated independently from the geodetic data and the offset seismic reflector, are not statistically significant. The MSSM represents an important resource for investigating Malawi's increasing seismic risk and provides a framework for incorporating active fault data into seismic hazard assessment elsewhere in the East African Rift and other tectonically active regions.

Correlation Dimension in Sumatra Island Based on Active Fault, Earthquake Data, and Estimated Horizontal Crustal Strain to Evaluate Seismic Hazard Functions (SHF)

This study intends to evaluate the possible correlation between the correlation dimension (DC) and the seismic moment rate for different late Quaternary active fault data, shallow crustal earthquakes, and GPS on the island of Sumatra Probabilistic Seismic Hazard Analysis (PSHA). The seismicity smoothing was applied to estimate the DC of active faults (DF) and earthquake data (DE) and then to correlate that with the b-value, which will be used to identify seismic hazard functions (SHF) along with the Sumatra Fault Zone (SFZ). The seismicity based on GPS data was calculated by the seismic moment rate that is estimated based on pre-seismic horizontal surface displacement data. The correlation between DF, DE, and the b-value was analyzed, and a reasonable correlation between the two seismotectonic parameters, DF-b, and DE-b, respectively, could be found. The relatively high DC coincides with the high seismic moment rate model derived from the pre-seismic GPS data. Furthermore, the SHF curve of total probability of exceedance versus the mean of each observation point’s peak ground acceleration (PGA) shows that the relatively high correlation dimension coincides with the high SHF. The results of this study might be very beneficial for seismic mitigation in the future.

Determination of the Fractal Dimension of the Active Fault Data along the East Anatolian Fault Zone

The current study has analyzed active fault data along the East Anatolian Fault Zone (EAFZ) applying both manual (classic) and modern versions of the box counting method. The EAFZ active fault dataset used for analysis was taken from the Geoscience Map Viewer and the Drawing Editor from the website of the General Directorate of Mineral Research and Exploration. The study covered an area stretching from Karlıova in the north to Kırıkhan in the south. The fractal analysis of the earthquake surface rupture and the Holocene fault data was performed. Fractal dimensions of the EAFZ active-fault data were calculated for 15 boxes and compared with correlation coefficient values. The calculated fractal dimension values were found to vary with the density of the active-fault data falling into the boxes. The maximum fractal dimension value D1 was determined for Karlıova and its surroundings, which can be associated with the fault density due to the branching geometry.

CCAF-DB: the Caribbean and Central American active fault database

Abstract. A database of ∼250 active fault traces in the Caribbean and Central American regions has been assembled to characterize the seismic hazard and tectonics of the area, as part of the Global Earthquake Model (GEM) Foundation's Caribbean and Central American Risk Assessment (CCARA) project. The dataset is available in many vector GIS formats and contains fault trace locations as well as attributes describing fault geometry and kinematics, slip rates, data quality and uncertainty, and other metadata as available. The database is public and open source (available at: https://github.com/GEMScienceTools/central_am_carib_faults, last access: 23 March 2020), will be updated progressively as new data become available, and is open to community contribution. The active fault data show deformation in the region to be centered around the margins of the Caribbean plate. Northern Central America has sinistral and reverse faults north of the sinistral Motagua–Polochic fault zone, which accommodates sinistral Caribbean–North American relative motion. The Central Highlands in Central America extend east–west along a broad array of normal faults, bound by the Motagua–Polochic fault zone in the north and trench-parallel dextral faulting in the southwest between the Caribbean plate and the Central American forearc. Faulting in southern Central America is complicated, with trench-parallel reverse and sinistral faults. The northern Caribbean–North American plate boundary is sinistral off the shore of Central America, with transpressive stepovers through Jamaica, southern Cuba and Hispaniola. Farther east, deformation becomes more contractional closer to the Lesser Antilles subduction zone, with minor extension and sinistral shear throughout the upper plate, accommodating oblique convergence of the Caribbean and North American plates.

Failures of masonry dwelling triggered by East Anatolian Fault earthquakes in Turkey

Turkey is located on active fault zones such as the East Anatolian Fault (EAF), the North Anatolian Fault (NAF) and the Anatolian-Aegean Subduction Zone (AASZ). Ground seismicity activities of the NAF zone are relatively active compared with other faults. Eleven high-intensity earthquakes have been produced on this fault zone since 1939. Whereas the EAF zone was relatively quiescent in the last century, on the basis of historical records, destructive seismic activities occurred on the EAF zone in the last two decades. In this study, the rupture reason of faults, updated active fault data, and seismic maps are presented briefly. Moreover, failure reasons and failure mechanism of conventional masonry structures damaged from seismic ground motions on the EAF zone are evaluated in detail. Possible solutions are suggested on the basis of seismic codes. For this purpose, EAF-sourced earthquakes, i.e. 2003 Bingöl, 2010 Kovancılar (Elazığ), 2011 Maden (Elazığ), 2011 Tabanlı (Van) and Edremit (Van) hit in last two decades on this fault are investigated. Failures of conventional masonry buildings triggered from these earthquakes are assessed. Statistical evaluation, damage of earthquakes and failure pattern are deeply investigated and revealed. Eventually, one of the most significant reasons of severe damage or collapse to masonry structures due to this seismicity is the inability to construct the structures according to the requirements of seismic codes.

Neotectonics, active tectonics and earthquake geology： terminology, applications and advances

Neotectonics and active tectonics are sub-disciplines of tectonics that study the process of recent tectonic deformation and tectonic geomorphic evolution on the Earth. The time scale of neotectonics research is closely related to the geodynamics of a specific region; it typically concerns geological processes at time scales from Ma to ka, and emphasizes on the relationship between the past and present tectonic deformation. On the other hand, research in active tectonics pays greater attention to geological–geomorphological processes since 100˜150ka, and focuses on present and future tectonic deformation. Research on neotectonics and active tectonics for seismic hazard assessment is a significant aspect of earthquake geology work. This, along with other related researches, is the primary basis of earthquake forecasting and prediction, urban and rural earthquake prevention, disaster mitigation, and project planning and design for effective circumvention and mitigation of geological hazards caused by active faults. Recent advances in these fields have indicated that the fast development and application of Quaternary chronology, open access space observation, and geographic information system (GIS), have substantially increased the level and precision of quantitative research on neotectonic evolution, tectonic morphology, fault activity and palaeo-seismology. This has led to the promotion and growth of digitalization and sharing of active fault data, and has also improved the reliability and accuracy of seismic hazard assessment. However, in countries and areas with high density of active faults and complex tectonic systems, such as China, research on neotectonics and active tectonics for seismic hazard assessment needs to be even further strengthened. There is a need for fast and effective regional surveying of active faults by the use of remote sensing and Digital Elevation Models (DEM) imaging, so as to study active structural systems. Therefore, to consolidate the geological foundation for prevention and mitigation of seismogeological disasters. Besides, the relationship between fault activity and risk should be distinguished, and attention should be paid to areas having strong-earthquake risk in stable continental regions and having low-slip-rate faults.

A model of active faulting in New Zealand

Active fault traces are a surface expression of permanent deformation that accommodates the motion within and between adjacent tectonic plates. We present an updated national-scale model for active faulting in New Zealand, summarize the current understanding of fault kinematics in 15 tectonic domains, and undertake some brief kinematic analysis including comparison of fault slip rates with GPS velocities. The model contains 635 simplified faults with tabulated parameters of their attitude (dip and dip-direction) and kinematics (sense of movement and rake of slip vector), net slip rate and a quality code. Fault density and slip rates are, as expected, highest along the central plate boundary zone, but the model is undoubtedly incomplete, particularly in rapidly eroding mountainous areas and submarine areas with limited data. The active fault data presented are of value to a range of kinematic, active fault and seismic hazard studies.

Stability of the regional stress field in central Japan during the late Quaternary inferred from the stress inversion of the active fault data

We analyzed 169 geological fault‐slip data from 37 active faults in central Japan to investigate the late Quaternary stress field stability. Modern stress states have been documented with unprecedented accuracy; however, their stability over time scales beyond instrumental observations is inadequately understood. Because the stress field has changed in the geological past, we compared present stress conditions in central Japan, determined from geophysical observations, with conditions determined by inverting the fault‐slip data from active faults that exhibited cumulative displacement for the past ∼105years. The maximum stress axis obtained from fault‐slip data trends ESE–WNW. This state of stress accounts for 97% of the data and supports the fact that oblique faults with reverse and strike‐slip senses are interlaced in the region. The optimal stress is similar to the present stress state, indicating that the stress field in central Japan has been uniform and stable over the past ∼105 years.

Testing various seismic potential models for hazard estimation against a historical earthquake catalog in Japan

The classic zoning method and spatial smoothing of seismicity were used with seismicity, GPS, and late Quaternary fault data to develop time-invariant seismic potential models of shallow crustal earthquakes in the Japanese islands that were then tested against a 400-year Japanese historical earthquake catalog. The results demonstrated that the models so developed for seismic hazard estimation did not necessarily reproduce the observed seismicity. In some cases they were even worse than the Reference Model that assumes a uniform earthquake potential over all of the Japanese islands. A subsequent analysis of the original dataset once it had been divided into two subsets based on time indicated that the present-day spatial distribution of small earthquakes and surface horizontal strain are much affected by previous large earthquakes. Two sources of information were the most effective: regionalized seismicity of small earthquakes and the active fault data. Two models using each of them were not only successful, but also robust. A model combining the distributions of small and moderate-size earthquakes proposed by Frankel in 1995 was also effective for modeling the distributed sources, which are unrelated to the faults. In this study, we tested the spatial variation of the likelihood of large earthquakes with M ≥ 6.8.

FEASIBILITY AND PROBLEMS OF EARTHQUAKE DISASTER REDUCTION MEASURES BASED ON ACTIVE FAULT DATA

Active fault data have been more widely and closely investigated and extensive data have also been collected. However, there are only a few examples related to land use planning for disaster reduction measures based on active fault data. The purpose of this study is (1) to categorize the disaster reduction measures, and (2) to examine problems and important factors for promoting disaster reduction measures based on a questionnaire survey. The cases of the measures that are able to be distinguished included building restriction, nonconstruction restriction, and risk communication. The questionnaire survey was conducted with the residents of Yokosuka city. The results of analyses showed that disaster reduction measures based on active fault data tended to be approximately accepted. Other results indicated that as the public's understanding related to earthquake risk and risk mitigation measures increases, the awareness of risk reduction measures based on active fault data is promoted, and the objectives of disaster reduction measures would be realized.

Deterministic and probabilistic seismic hazard analyses in Thailand and adjacent areas using active fault data

AbstractSeismic hazards in Thailand and adjacent areas were analyzed mainly on the basis of geological fault data. We identified 55 active fault zones using remote-sensing data on earthquake source parameters derived from both active fault data and earthquake catalogues. We selected strong ground-motion attenuation models by comparing the application of several candidate models with strong ground-motion data recorded in Thailand. Both deterministic (DSHA) and probabilistic (PSHA) approaches were used—DSHA for the design of critical construction and PSHA for the design of non-critical construction. We also applied two frequency-magnitude models in the PSHA approach: the exponential magnitude distribution model and the characteristic earthquake model. The seismic hazard results obtained using the deterministic and probabilistic approaches are not equivalent. The resulting DSHA map reveals extremely high seismic hazard levels in some areas of Thailand and in surrounding countries, while the PSHA map reveals a seismic hazard distribution similar to that of the DSHA but with lower seismic hazard levels. The areas of high seismic hazard include countries neighboring Thailand, such as Myanmar, Laos, Vietnam, and Indonesia (Sumatra Island), and areas within Thailand itself, primarily those areas in northern, western, and southern Thailand that are dominated by active fault zones.

The Database of Individual Seismogenic Sources (DISS), version 3: Summarizing 20 years of research on Italy's earthquake geology

This paper describes the main characteristics, the evolution, and the structure of the Database of Individual Seismogenic Sources (DISS) and particularly of its release of early 2007. The Database contains the results of the investigations of the active tectonics in Italy during the past 20 years. The first two sections of this paper document the recent evolution in mapping and archiving Italian active fault data in relation to important achievements in the understanding of Italian tectonics, some of which were spurred by significant earthquakes. The central sections describe the current structure of the Database, the reasons for its assumptions and data categories, its current contents, its evolution through several years of improvements. The last section describes how the current contents of the Database correspond with the existing strain and stress data available from focal mechanism, borehole breakout, and GPS data for the whole of Italy. The Database supplies a fresh and unified view of active and seismogenic processes in Italy by building on basic physical constraints concerning rates of crustal deformation, on the continuity of deformation belts and on the spatial relationships between adjacent faults, both at the surface and at depth.

THE SUMATRAN FAULT ZONE — FROM SOURCE TO HAZARD

The substantial portion of the dextral component of the Sumatran oblique convergence is accommodated by the Sumatran fault. This 1900 km-long active strike-slip fault zone runs along the backbone of Sumatra pose seismic and fault hazards to dense population on and around the fault zones. The Sumatran fault is highly segmented, and consists of 20 major geometrically defined segments, which range in length from about 60 to 200 km. These segment lengths influenced seismic source dimensions and have limited the magnitudes of large historical fault ruptures to between Mw6.5 and about 7.7. Slip rates along the fault increase northwestward, from about 5 mm/yr around the Sunda Strait to 27 mm/yr around Toba Lake. These sliprate values provide a quantitative basis for calculation of average expected recurrence periods for large earthquakes on each segment. Deterministic and probabilistic hazard assessments are constructed based on these active fault data.

An analysis on surface geometry of reverse faults in Japan based on digital active fault data

An analysis on surface geometry of reverse faults in Japan based on digital active fault data

Comparison of the Historical Record of Earthquake Hazard with Seismic- Hazard Models for New Zealand and the Continental United States

We compare the historical record of earthquake hazard experienced at 78 towns and cities (sites) distributed across New Zealand and the continental United States with the hazard estimated from the national probabilistic seismic-hazard (psh) models for the two countries. The two psh models are constructed with similar methodologies and data. Our comparisons show a tendency for the psh models to slightly exceed the historical hazard in New Zealand and westernmost continental United States interplate regions, but show lower hazard than that of the historical record in the continental United States intraplate region. Factors such as non- Poissonian behavior, parameterization of active fault data in the psh calculations, and uncertainties in estimation of ground-motion levels from historical felt intensity data for the interplate regions may have led to the higher-than-historical levels of hazard at the interplate sites. In contrast, the less-than-historical hazard for the remaining continental United States (intraplate) sites may be largely due to site conditions not having been considered at the intraplate sites, and uncertainties in correlating ground-motion levels to historical felt intensities. The study also highlights the importance of evaluating psh models at more than one region, because the conclusions reached on the basis of a solely interplate or intraplate study would be very different.

New active fault data and seismic hazard estimates for west Otago, New Zealand

We present new maps and slip rate estimates for the Blue Mountain and Spylaw Faults of west Otago, and a re‐evaluation of the probabilistic seismic hazard for the area. Our mapping has resulted in an extension of the active section of the Blue Mountain Fault by about a factor of two, and reduction of the slip rates for the two faults by about a factor of two to five from the previous estimates. The incorporation of these revised fault data into the national seismic hazard model has resulted in the elimination of a zone of anomalously high seismic hazard in the national hazard maps, leaving behind a smooth gradient of increasing hazard from east to west across Otago towards the plate boundary. The study serves to show the magnitude of changes to seismic hazard estimates that result from significant changes to the recurrence parameters of individual fault sources. Future changes to hazard estimates may also be observed elsewhere in the country (e.g., Taupo Volcanic Zone) when significant updates to fault source data are made in the seismic hazard model.

Active faults in Eurasia: general remarks

The database and map of active faults of Eurasia, 1:5,000,000, have been compiled according to the ILP Project II-2 “World Map of Major Active Faults.” The map shows the complicated distribution of active faulting. The major faults group in broad mobile belts between relatively weakly faulted parts of the main plates. The faults form the plates, microplates and crustal blocks boundaries there and are accompanied by deformation of the boundary areas. Using active fault data for the seismic hazard assessment (estimation of maximum possible magnitudes of earthquakes in fault zones), it is necessary to take into account the total neotectonic activity of the territory and average rate and sense of motion on the fault. Because trenching gives a possibility to determine only vertical earthquake offset on a fault, it is necessary to make corrections for strike–slip faults to estimate the earthquake magnitude by using this parameter.

Use of Active Fault Data versus Seismicity Data in the Evaluation of Seismic Hazard in the Granada Basin (Southern Spain)

In this article we evaluate the seismic hazard in the Granada Basin (southern Spain), using for the first time the slip rate of known active faults. Our study, as an attempt to compute seismic hazard using active fault data in low to moderate seismicity regions, relies on a complete database of these faults containing information relevant to their seismic potential. We obtain peak ground acceleration values above 0.4g for a return period of 475 years. This result is compared with previous evaluations carried out on the basis of the historical seismicity of the area and the application of the well-known theorem of total probability. In these cases, maximum values of 0.2g are obtained. We explain the discrepancies found between the slip rate-derived and seismicity-derived estimates of seismic hazard as owing to the different strikes of the faults in relation to the directions of the main stresses affecting the Granada Basin, in the context of the Betic Cordilleras, some of them with evidence of aseismic slip.

地震の活動履歴とモデルの不確定性を考慮した地震危険度の解析的評価

Appropriate modeling of seismic load intensity is one of the critical factors for the reliability assessment of a structure. Using active fault data and attenuation formula, this paper presents an analytical method to evaluate cumulative distribution function (cdf) of n-year maximum value of ground motions and response spectra at a site efficiently considering various kinds of uncertainties including magnitude of earthquakes, recurrence periods, and accuracy of attenuation formula. Numerical examples show that the cdf of the n-year maximum value is different from site to site. The sensitivity of the cdf to the uncertainties to the probabilistic models is also investigated.

ASSESSMENT OF SEISMIC HAZARD AND MICROZONING IN THE PHILIPPINES

Seismic hazard and microzoning of the Philippines are presented. Seismic hazard analysis of the Philippines on rock-surface level is done to all land areas of the country. The analysis includes both the historical earthquake occurrences and active fault data. Ground motion amplification corrections based on surface geology is determined based on the representative soil softness index of each geology type. The resulting amplification corrections are applied to the rock-surface seismic hazard of the Philippines. A significant increase of seismic hazard by applying the amplification corrections is shown for the city of Manila.