scholarly journals Temporal and spatial earthquake clustering revealed through comparison of millennial strain-rates from 36Cl cosmogenic exposure dating and decadal GPS strain-rate

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Francesco Iezzi ◽  
Gerald Roberts ◽  
Joanna Faure Walker ◽  
Ioannis Papanikolaou ◽  
Athanassios Ganas ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Strain Rate ◽  
Active Faults ◽  
Slip Rate ◽  
Normal Faults ◽  
Fault Activity ◽  
Exposure Dating ◽  
Extensional Strain ◽  
Temporal And Spatial

AbstractTo assess whether continental extension and seismic hazard are spatially-localized on single faults or spread over wide regions containing multiple active faults, we investigated temporal and spatial slip-rate variability over many millennia using in-situ 36Cl cosmogenic exposure dating for active normal faults near Athens, Greece. We study a ~ NNE-SSW transect, sub-parallel to the extensional strain direction, constrained by two permanent GPS stations located at each end of the transect and arranged normal to the fault strikes. We sampled 3 of the 7 seven normal faults that exist between the GPS sites for 36Cl analyses. Results from Bayesian inference of the measured 36Cl data implies that some faults slip relatively-rapidly for a few millennia accompanied by relative quiescence on faults across strike, defining out-of-phase fault activity. Assuming that the decadal strain-rate derived from GPS applies over many millennia, slip on a single fault can accommodate ~ 30–75% of the regional strain-rate for a few millennia. Our results imply that only a fraction of the total number of Holocene active faults slip over timescales of a few millennia, so continental deformation and seismic hazard are localized on specific faults and over a length-scale shorter than the spacing of the present GPS network over this time-scale. Thus, (1) the identification of clustered fault activity is vital for probabilistic seismic hazard assessments, and (2) a combination of dense geodetic observations and palaeoseismology is needed to identify the precise location and width of actively deforming zones over specific time periods.

Across-strike variations of fault slip-rates constrained using in-situ cosmogenic 36Cl concentrations.

2020 ◽  
Author(s):  
Francesco Iezzi ◽  
Gerald Roberts ◽  
Joanna Faure Walker ◽  
Ioannis Papanikolaou ◽  
Athanassios Ganas ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Strain Rate ◽  
Active Faults ◽  
Slip Rate ◽  
High Temporal Resolution ◽  
Strain Rates ◽  
Time Intervals ◽  
The Holocene ◽  
Regional Strain

<p>It is important to constrain the spatial distribution of strain-rate in deforming continental material because this underpins calculations of continental rheology and seismic hazard. To do so, it is becoming increasingly common to use combinations of GPS and historical and instrumental seismicity data to constrain regional strain-rate fields. However, GPS geodetic sites, whether permanent or campaign stations, tend to be widely-spaced relative to the spacing of active faults with known Holocene offsets. At the same time, the interpretation of seismicity data can be difficult due to lack of historical seismicity in cases where local fault recurrence intervals are longer than the historical record. This causes uncertainty on how regional strain-rates are partitioned in time and space, and hence with uncertainty regarding calculations of continental rheology and seismic hazard. To overcome this issue, we have gained high temporal resolution slip-rate histories for three parallel faults using in situ <sup>36</sup>Cl cosmogenic dating of the exposure of three parallel normal fault planes that have been progressively exhumed by earthquakes. We study the region around Athens, central Greece, where there also exists a relatively-dense GPS network and extensive records of instrumental and historical earthquakes. This allows to compare regional, decadal strain-rates measured with GPS geodesy with strain-rates across the faults implied by slip since ~40,000 years BP. We show that faults have all had episodic behaviour during the Holocene, with alternating earthquake clusters and periods of quiescence through time. Despite the fact that all three faults have been active in the Holocene, each fault slips in discrete time intervals lasting a few millennia, so that only one fault accommodates strain at any time. We show that magnitudes of strain-rates during the high slip-rate episodes are comparable with the regional strain-rates measured with GPS (fault strain-rates are 50-100% of the value of GPS regional strain-rate). Thus, if the GPS-derived strain-rate applies over longer time intervals, it appears that single faults dominate the strain-accumulation at any given time, with crustal deformation and seismic hazard localised within a distributed network of faults.</p><p> </p>

scholarly journals Uncertainty in strain-rate from field measurements of the geometry, rates and kinematics of active normal faults: Implications for seismic hazard assessment

2020 ◽  
Author(s):  
Claudia Sgambato ◽  
Joanna P. Faure Walker ◽  
Gerald P. Roberts
Keyword(s):  
Seismic Hazard ◽  
Strain Rate ◽  
Structural Complexity ◽  
Slip Rate ◽  
Seismic Hazard Assessment ◽  
Field Measurements ◽  
Structural Data ◽  
Fault Scarp ◽  
Normal Faults ◽  
Multiple Measurements

<p>Multiple measurements of the geometry, kinematics and rates of slip across the well-exposed Auletta fault scarp (Campania, Italy) are presented, and we use these in order to investigate: (1) the spatial resolution of field measurements needed to accurately calculate a representative strain-rate for seismic hazard calculations; (2) what aspects of the geometry and kinematics would introduce uncertainty in calculated strain-rate, if those are not measured in the field. Our results show that the magnitude of the post-glacial maximum (15±3 ka) throw gradually decreases towards the tip of the fault, but variations are observed along strike, across areas of structural complexity such as along-strike bends in the fault plane where the fault dip is greater. We find that if such variations are unnoticed, different values of strain-rate would be produced, and hence different values would result in seismic hazard calculations. To demonstrate this, we calculate the strain-rate across the Auletta fault using all our measurements, and subsequently degrade the dataset removing one measurement at a time and recalculating the implied strain-rate at each step. The results show that excluding measurements can alter strain-rate results beyond 1 σ uncertainty, thus we suggest caution when using only one measurement of slip-rate along a fault for calculating hazard, as a full understanding of the potential implied errors needs consideration. Furthermore, we investigate the effect of approximating the throw profile along the fault using boxcar and triangular slip distributions; we show that this can underestimate or overestimate the strain-rate, with results in the range of 72–237% of our most detailed strain-rate calculation. We suggest that improved understanding of the potential implied errors in strain-rate calculations from field structural data should be implemented in seismic hazard calculations.</p>

Uplift and active tectonics of southern Albania inferred from incision of alluvial terraces

2009 ◽  
Vol 71 (3) ◽  
pp. 465-476 ◽  
Author(s):  
J. Carcaillet ◽  
J.L. Mugnier ◽  
R. Koçi ◽  
F. Jouanne
Keyword(s):  
Active Faults ◽  
Active Tectonics ◽  
Slip Rate ◽  
Age Dating ◽  
Normal Faults ◽  
Published Data ◽  
Fluvial Terraces ◽  
Thrust System ◽  
Alluvial Terraces

AbstractIn Albania, the Osum and Vjoje rivers cross the active graben system and the active frontal thrust system of the Albanides. The effects of climatic and geodynamic forcing on the development of these two rivers were investigated by the means of field mapping, topographic surveying and absolute exposure-age dating. We established the chronology of terraces abandonment from the compilation of new dating (14C and in situ produced 10Be) and previously published data. We identified nine fluvial terraces units developed since Marine Isotope Stage 6 up to historic times. From this reconstituted history, we quantified the vertical uplift on a time scale shorter than the glacial climatic cycle. Regional bulging produces an overall increase of the incision rate from the west to the east that reaches a maximum value of 2.8 m/ka in the hinterland. Local pulses of incision are generated by activation of normal faults. The most active faults have a SW–NE trend and a vertical slip rate ranging from 1.8 to 2.2 m/ka. This study outlines the geodynamic control in the development of rivers flowing through the Albanides on the scale of 103–105ka.

scholarly journals Methodology for Earthquake Rupture Rate estimates of fault networks: example for the Western Corinth Rift, Greece

2017 ◽  
Author(s):  
Thomas Chartier ◽  
Oona Scotti ◽  
Hélène Lyon-Caen ◽  
Aurélien Boiselet
Keyword(s):  
Active Faults ◽  
Slip Rate ◽  
Seismic Hazard Assessment ◽  
System Level ◽  
Fault System ◽  
Normal Faults ◽  
Accurate Estimation ◽  
Probabilistic Seismic Hazard Assessment ◽  
Earthquake Rupture ◽  
Multiple Faults

Abstract. Modelling the seismic potential of active faults is a fundamental step of probabilistic seismic hazard assessment (PSHA). An accurate estimation of the rate of earthquakes on the faults is necessary in order to obtain the probability of exceedance of a given ground motion. Most PSHA studies consider faults as independent structures and neglect the possibility of multiple faults or fault segments rupturing simultaneously (Fault to Fault -FtF- ruptures). The latest Californian model (UCERF-3) takes into account this possibility by considering a system level approach rather than an individual fault level approach using the geological , seismological and geodetical information to invert the earthquake rates. In many places of the world seismological and geodetical information long fault networks are often not well constrained. There is therefore a need to propose a methodology relying only on geological information to compute earthquake rate of the faults in the network. In this methodology, similarly to UCERF-3, a simple distance criteria is used to define FtF ruptures and consider single faults or FtF ruptures as an aleatory uncertainty. Rates of earthquakes on faults are then computed following two constraints: the magnitude frequency distribution (MFD) of earthquakes in the fault system as a whole must follow an imposed shape and the rate of earthquakes on each fault is determined by the specific slip-rate of each segment depending on the possible FtF ruptures. The modelled earthquake rates are then confronted to the available independent data (geodetical, seismological and paleoseismological data) in order to weigh different hypothesis explored in a logic tree. The methodology is tested on the Western Corinth Rift, Greece (WCR) where recent advancements have been made in the understanding of the geological slip rates of the complex network of normal faults which are accommodating the ~15 mm/yr North-South extension. Modelling results show that geological, seismological extension rates and paleoseismological rates of earthquakes cannot be reconciled with only single fault rupture scenarios and require hypothesising a large spectrum of possible FtF rupture sets. Furthermore, in order to fit the imposed regional Gutenberg-Richter MFD target, some of the slip along certain faults needs to be accommodated either with interseismic creep or as post-seismic processes. Furthermore, individual fault’s MFDs differ depending on the position of each fault in the system and the possible FtF ruptures associated with the fault. Finally, a comparison of modelled earthquake rupture rates with those deduced from the regional and local earthquake catalogue statistics and local paleosismological data indicates a better fit with the FtF rupture set constructed with a distance criteria based on a 5 km rather than 3 km, suggesting, a high connectivity of faults in the WCR fault system.

scholarly journals 25,000 Years Long Seismic Cycle in a Slow Deforming Continental Region of Mongolia

2021 ◽  
Author(s):  
Laurent Bollinger ◽  
Yann Klinger ◽  
Steven Forman ◽  
Odonbaatar Chimed ◽  
Amgalan Bayasgalan ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Active Faults ◽  
Ground Surface ◽  
Slip Rate ◽  
Seismic Hazard Assessment ◽  
Return Time ◽  
Fault Behavior ◽  
Seismogenic Structures ◽  
Cumulative Deformation ◽  
Large Earthquakes

Abstract The spatial distribution of large earthquakes in Slowly Deforming Continental Regions (SDCR) is poorly documented and, thus, has often been deemed to be random. Unlike in high strain regions, where seismic activity concentrates cyclically along major active faults, earthquakes in SDCR may seem to occur more erratically in space and time. This questions classical fault behavior models, posing paramount issues for seismic hazard assessment. Here, we investigate the M7, 1967, Mogod earthquake in Mongolia, a region recognized as a SDCR. Despite the absence of visible cumulative deformation at the ground surface, we found evidence for at least 3 surface rupturing earthquakes during the last 50,000 years, associated to a slip-rate of 0,06 ± 0,01 mm/yr. These results show that in SDCR, like in faster deforming regions, deformation localizes on specific structures. However, the excessive length of return time for large earthquakes along these structures makes it more difficult to recognize earthquake series, and could conversely lead to the misconception that in SDCR earthquakes would be randomly located. Thus, our result emphasizes the need for systematic appraisal of the potential seismogenic structures in SDCR in order to lower the uncertainties associated with the seismogenic sources in seismic hazard models.

Towards a comprehensive European fault database for induced seismic hazard research

2020 ◽  
Author(s):  
Serge Van Gessel ◽  
Harry Middelburg ◽  
Esther Hintersberger ◽  
Tine Larsen ◽  
Sabrine Ben Rhouma ◽  
...  
Keyword(s):  
Stress State ◽  
Seismic Hazard ◽  
Anthropogenic Activities ◽  
Active Faults ◽  
The European Union ◽  
Fault Systems ◽  
Geological Conditions ◽  
Seismogenic Faults ◽  
And Behavior

<p><strong>Towards a comprehensive European fault database for induced seismic hazard research</strong></p><p>Seismogenic faults and fault systems in tectonically active regions are extensively studied as a source of seismic hazard and especially of high magnitude natural earthquakes. Global research has already resulted in several databases and models presenting location, characteristics and kinematic behavior of such faults (e.g. GEM Global Active Faults Database, SHARE European Database of Seismogenic Faults, USGS Quaternary faults database).</p><p>Faults that are inactive under present-day geological conditions are far more abundant, yet less-well documented. Nevertheless, these faults can potentially pose significant hazards under anthropogenic activities, particularly when the stress state of such faults is influenced by adjacent active fault systems (e.g. Northern Italy). Subsurface extraction and injection of fluids can either alter the in-situ stress state to a level exceeding the critical stress threshold (e.g. through pressure-induced compaction) or reduce the fault strength to a point where natural stresses can trigger fault movements (e.g. through the invasion of fluids into the fault zone). Well-known cases are reported among others in Basel – Switzerland (geothermal stimulation), Oklahoma – US (waste water injection) and Groningen – The Netherlands (conventional hydrocarbon extraction).</p><p>Here, we present the development of a pan-European fault database by the project GeoERA-HIKE. The database incorporates the locations, geometries, characteristics and scientific references of both active and inactive faults and fault systems and will be complementary to existing databases of seismogenic faults. The database information is derived from national mapping studies and local assessments by the European Geological Survey Organizations and includes, amongst others, surface outcrop observations, geophysical monitoring, boreholes and geological modelling studies.</p><p>The primary goal of the database is to support induced hazard studies with better access to harmonized data and knowledge on fault characteristics and behavior. The correlation of fault systems across Europe with a generic semantic concepts framework provides better insight into the genetic links between active and inactive fault systems within the greater structural geological development of Europe. The integration of data from different geoscience disciplines will improve the understanding of in-situ characteristics and behavior. Ultimately, the database is intended to become a collaborative tool for future fault characterization and research by geoscience institutes.</p><p>The GeoERA-HIKE project has received funding from the European Union’s Horizon 2020 research and innovation programme under agreement No. 731166</p>

scholarly journals Geologic and geodetic constraints on the seismic hazard of Malawi’s active faults: The Malawi Seismogenic Source Database (MSSD)

2021 ◽  
Author(s):  
Jack N. Williams ◽  
Luke N. J. Wedmore ◽  
Åke Fagereng ◽  
Maximilian J. Werner ◽  
Hassan Mdala ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Active Fault ◽  
Active Faults ◽  
Slip Rate ◽  
Slip Rates ◽  
Source Database ◽  
Seismogenic Sources ◽  
Seismogenic Source ◽  
Recurrence Intervals ◽  
Seismic Reflector

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 Database (MSSD), which describes the seismogenic properties of faults that have formed during East African rifting in Malawi. We first use empirical observations to geometrically classify active faults into section, fault, and multi-fault 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 is estimated to be 75 ka based on dated core. 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 regional strain distribution 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 of outcomes from a logic tree used in these calculations. We find that for sources in the Lake Malawi’s North Basin, where slip rates can be derived from both the geodetic data and the offset seismic reflector, the slip rate estimates are within error of each other, although those from the offset reflector are higher. Sources in the MSSD are 5–200 km long, which implies that large magnitude (MW 7–8) earthquakes may occur in Malawi. Low slip rates (0.05–2 mm/yr), however, mean that the frequency of such events will be low (recurrence intervals ~103–104 years). The MSSD represents an important resource for investigating Malawi’s increasing seismic risks and provides a framework for incorporating active fault data into seismic hazard assessment in other tectonically active regions.

scholarly journals Potentially active normal faulting zone identified in the eastern margin of Palu City, Central Sulawesi, Indonesia

2021 ◽  
Vol 873 (1) ◽  
pp. 012071
Author(s):  
Anggraini Rizkita Puji ◽  
Mudrik Rahmawan Daryono ◽  
Danny Hilman Natawidjaja
Keyword(s):  
Active Faults ◽  
Digital Terrain Model ◽  
Slip Rate ◽  
Normal Fault ◽  
Provincial Government ◽  
Economic Losses ◽  
Normal Faults ◽  
Normal Faulting ◽  
Eastern Margin ◽  
Central Sulawesi

Abstract The 2018 Mw 7.5 earthquake in Palu, Central Sulawesi, resulting in ~2,000 fatalities and estimated economic losses of ~22.8 trillion Indonesian Rupiah, according to the report of BAPPENAS and Central Sulawesi Provincial-Government. Therefore, it is necessary to prevent similar disaster in the future by further detailed studies of any other potential sources that are capable of generating such hazards. Palu City is in the vast depression valley bordered by mountains in its eastern and western margins. The 2018 earthquake source is the Palukoro Fault, which runs through the western margin of onshore Palu Valley then continued under the bay. Along the eastern margin of the valley, we also identified a wide zone of many potentially active faults strands orienting N-S and NW-SE, showing predominantly normal faulting. These faults are observed from their normal fault scarps as inspected from Light Detection and Ranging Digital Terrain Model (LiDAR DTM) data with 90-cm resolution and field ground checks. The faults deformed the old terrace sediments (Late Pleistocene, ~125 kya), but it is unclear whether they also cut the Holocene young alluvial like the ruptured fault of 2018 event. Further paleoseismology investigation is then necessary to obtain further information about these potentially-active normal faults, including their slip-rate and the past ruptures.

scholarly journals Late Quaternary fault activity in the Western Carpathians: evidence from the Vikartovce Fault (Slovakia)

2011 ◽  
Vol 62 (6) ◽  
pp. 563-574 ◽  
Author(s):  
Rastislav Vojtko ◽  
František Marko ◽  
Frank Preusser ◽  
Ján Madarás ◽  
Marianna Kováčová
Keyword(s):  
System Analysis ◽  
Late Quaternary ◽  
Active Faults ◽  
Slip Rate ◽  
Geological Structure ◽  
Luminescence Dating ◽  
Western Carpathians ◽  
Normal Displacement ◽  
Fault Activity ◽  
Central Western Carpathians

Late Quaternary fault activity in the Western Carpathians: evidence from the Vikartovce Fault (Slovakia)The Cenozoic structure of the Western Carpathians is strongly controlled by faults. The E-W striking Vikartovce fault is one of the most distinctive dislocations in the region, evident by its geological structure and terrain morphology. This feature has been assumed to be a Quaternary reactivated fault according to many attributes such as its perfect linearity, faceted slopes, the distribution of travertines along the fault, and also its apparent prominent influence on the drainage network. The neotectonic character of the fault is documented herein by morphotectonic studies, longitudinal and transverse valley profile analyses, terrace system analysis, and mountain front sinuosity. Late Pleistocene activity of the Vikartovce fault is now proven by luminescence dating of fault-cut and uplifted alluvial sediments, presently located on the crest of the tilted block. These sediments must slightly pre-date the age of river redirection. Considering the results of both luminescence dating and palynological analyses, the change of river course probably occurred during the final phase of the Riss Glaciation (135 ± 14 ka). The normal displacement along the fault during the Late Quaternary has been estimated to about 105-135 m, resulting in an average slip rate of at least 0.8-1.0 mm · yr-1. The present results identify the Vikartovce fault as one of the youngest active faults in the Central Western Carpathians.

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