Earthquake Recurrence Rates Research Articles

Geologic Input Databases for the 2025 Puerto Rico—U.S. Virgin Islands National Seismic Hazard Model Update: Crustal Faults Component

Abstract The last National Seismic Hazard Model (NSHM) for Puerto Rico and the U.S. Virgin Islands (PRVI) was published in 2003. In advance of the 2025 PRVI NSHM update, we created three geologic input databases to summarize new onshore and offshore fault source information in the northern Caribbean region between 62°–70° W and 16°–21° N. These databases, of fault sections, fault-zone polygons, and geologic estimates of fault activity (fault-slip rate and earthquake recurrence intervals) at specific sites, document updates to fault parameters used in prior seismic hazard models in PRVI. Fault sources were reviewed from published studies since 2003, which document substantial changes to the understanding of fault location, geometry, or activity. New fault section sources were added for features that meet the criteria of (1) length ≥7 km, (2) unequivocal evidence of recurrent tectonic Quaternary activity, and (3) documentation that is publicly available in a peer-reviewed source. In addition, we revised several broad areal sources, such as the Mona and Anegada extensional zones. The 2003 model included three fault sections and two fault-zone polygons (areal sources). These databases include 35 fault sections, 6 fault-zone polygons, and 51 earthquake geology sites. To characterize fault activity rates, slip-rate bins were assigned based on landscape expression and paleoseismic trench observations for faults without published slip-rate sites. Additional fault sources were evaluated but not included in these databases due to a lack of published information about fault location, geometry, or recurrent Quaternary activity. The PRVI NSHM 2025 geologic input databases describe crustal faulting; the geometries and coupling of Puerto Rico subduction zone and Muertos Trough models are considered in a separate database. Updates to the fault sections, fault-zone polygons, and earthquake geology databases can help inform the location and recurrence rate of damaging earthquakes in the PRVI NSHM implementation.

Magnitude and source area estimations of severe prehistoric earthquakes in the western Austrian Alps

Abstract. In slowly deforming intraplate tectonic regions such as the Alps only limited knowledge exists on the occurrence of severe earthquakes, their maximum possible magnitude, and their potential source areas. This is mainly due to long earthquake recurrence rates exceeding the time span of instrumental earthquake records and historical documentation. Lacustrine paleoseismology aims at retrieving long-term continuous records of seismic shaking. A paleoseismic record from a single lake provides information on events for which seismic shaking exceeded the intensity threshold at the lake site. In addition, when positive and negative evidence for seismic shaking from multiple sites can be gathered for a certain time period, minimum magnitudes and source locations can be estimated for paleo-earthquakes by a reverse application of an empirical intensity prediction equation in a geospatial analysis. Here, we present potential magnitudes and source locations of four paleo-earthquakes in the western Austrian Alps based on the integration of available and updated lake paleoseismic data, which comprise multiple mass-transport deposits on reflection seismic profiles and turbidites and soft-sediment deformation structures in sediment cores. The paleoseismic records at Plansee and Achensee covering the last ∼10 kyr were extended towards the age of lake initiation after deglaciation to obtain the longest possible paleoseismic catalogue at each lake site. Our results show that 25 severe earthquakes are recorded in the four lakes Plansee, Piburgersee, Achensee, and potentially Starnbergersee over the last ∼16 kyr, from which four earthquakes are interpreted to have left imprints in two or more lakes. Earthquake recurrence intervals range from ca. 1000 to 2000 years, with a weakly periodic to aperiodic recurrence behavior for the individual records. We interpret that relatively shorter recurrence intervals in the more orogen-internal archives Piburgersee and Achensee are related to enhanced tectonic loading, whereas a longer recurrence rate in the more orogen-external archive Plansee might reflect a decreased stress transfer across the current-day enhanced seismicity zone. Plausible epicenters of paleo-earthquake scenarios coincide with the current enhanced seismicity regions. Prehistoric earthquakes with a minimum moment magnitude (Mw) 5.8–6.1 have occurred around the Inn valley, the Brenner region, and the Fernpass–Loisach region and might have reached up to Mw 6.3 at Achensee. The paleo-earthquake catalogue might hint at a shift in severe earthquake activity near the Inn valley from east to west to east during postglacial times. ShakeMaps highlight that such severe earthquake scenarios do not solely impact the enhanced seismicity region of Tyrol but widely affect adjacent regions like southern Bavaria in Germany.

Climatic controls on travertine deposition in southern Tibet during the late Quaternary

Large volumes of travertine deposits are preserved at hydrothermal spring sites on the Tibetan Plateau (TP). Yet, most of these deposits are under-researched with respect to their diagenetic and depositional history and there is still very limited understanding of the tectonic and climatic influences on travertine precipitation in the arid high-altitude setting of Tibet. In this study, a detailed uranium-series dating campaign was carried out for the Qiusang travertine (~4270 m above sea level), southern Tibet that has been previously dated back to 486 thousand years ago (ka). Based on 42 new 230 Th/U ages, combined with geomorphological and sedimentological investigations, several travertine zones were identified and distinct travertine depositional phases constrained: 11.7–6.8 ka and ~ 13.4 ka (zone 1), 128–122 ka (zone 2), ~193 ka (zone 3), ~292 ka and 324 ka (zone 4), >317 ka (zone 5), ca. 415 to 470 ka (zone 6) and ca. 419 to 445 ka (zone 7). Comparison of these depositional phases with local and regional proxy records suggests that travertine accumulation at Qiusang occurred during main interglacials when monsoon precipitation peaked on the TP. This coincidence, together with a sensitive response of Tibetan hydrothermal spring activity to meteoric recharge, implies that climate controls the precipitation of large travertine volumes on orbital timescales on the plateau. We propose that (i) tectonic activity is of subordinate importance and influences travertine precipitation on the TP only episodically and on significantly shorter (i.e. centennial to millennial) timescales related to the recurrence rates of large earthquakes and that (ii) intensive monsoonal-driven groundwater recharge is required on top of tectonic activity for generating volumetrically significant travertine accumulations. Because of the high precipitation rates typical for hydrothermal spring carbonates, we conclude that travertine deposits on the TP could be utilized as valuable high-resolution proxy records of peak monsoon conditions in the currently arid to semi-arid landscape. Furthermore, the Qiusang travertine zone 7 is terraced and the travertine layers adjusted to a paleo-riverbed elevation ~30 m above the current river, allowing us to constrain fluvial incision to ~0.07 m/ka for the south-central sector of the TP since the Mid-Pleistocene. The abundant travertine occurrences in Tibet in combination with uranium-series dating can thus also provide detailed insights into earth surface dynamics and landscape evolution on the world highest plateau. • A detailed 230 Th/U dating campaign was conducted for the Qiusang travertine, Tibet. • Travertine deposition is restricted to interglacial conditions with peak monsoon. • Climatic controls on Tibetan travertine growth are on top of tectonic influences. • U Th ages of terraced travertines constrain a fluvial incision rate of ~0.07 m/ka.

Active Faulting in Lake Constance (Austria, Germany, Switzerland) Unraveled by Multi-Vintage Reflection Seismic Data

Probabilistic seismic hazard assessments are primarily based on instrumentally recorded and historically documented earthquakes. For the northern part of the European Alpine Arc, slow crustal deformation results in low earthquake recurrence rates and brings up the necessity to extend our perspective beyond the existing earthquake catalog. The overdeepened basin of Lake Constance (Austria, Germany, and Switzerland), located within the North-Alpine Molasse Basin, is investigated as an ideal (neo-) tectonic archive. The lake is surrounded by major tectonic structures and constrained via the North Alpine Front in the South, the Jura fold-and-thrust belt in the West, and the Hegau-Lake Constance Graben System in the North. Several fault zones reach Lake Constance such as the St. Gallen Fault Zone, a reactivated basement-rooted normal fault, active during several phases from the Permo-Carboniferous to the Mesozoic. To extend the catalog of potentially active fault zones, we compiled an extensive 445 km of multi-channel reflection seismic data in 2017, complementing a moderate-size GI-airgun survey from 2016. The two datasets reveal the complete overdeepened Quaternary trough and its sedimentary infill and the upper part of the Miocene Molasse bedrock. They additionally complement existing seismic vintages that investigated the mass-transport deposit chronology and Mesozoic fault structures. The compilation of 2D seismic data allowed investigating the seismic stratigraphy of the Quaternary infill and its underlying bedrock of Lake Constance, shaped by multiple glaciations. The 2D seismic sections revealed 154 fault indications in the Obersee Basin and 39 fault indications in the Untersee Basin. Their interpretative linkage results in 23 and five major fault planes, respectively. One of the major fault planes, traceable to Cenozoic bedrock, is associated with a prominent offset of the lake bottom on the multibeam bathymetric map. Across this area, high-resolution single channel data was acquired and a transect of five short cores was retrieved displaying significant sediment thickness changes across the seismically mapped fault trace with a surface-rupture related turbidite, all indicating repeated activity of a likely seismogenic strike-slip fault with a normal faulting component. We interpret this fault as northward continuation of the St. Gallen Fault Zone, previously described onshore on 3D seismic data.

Geodetic Constraints on Recent Subduction Earthquakes and Future Seismic Hazards in the Southwestern Coast of Mexico

AbstractThree major subduction earthquakes occurred on March 20, 2012 (Mw 7.4), February 16, 2018 (Mw 7.2), and June 23, 2020 (Mw 7.4) in the southwestern coast of Mexico, which caused fatalities, casualties, considerable damage, and raised safety concerns about future seismic hazards. We use satellite geodetic observations to invert for the slip distributions of the three events and then investigate their interactions. Coulomb Failure Stress (CFS) induced by their slip both on surrounding thrust and normal faults are calculated. The positive CFS changes, along with the spatial‐temporal seismicity evolution, approximate earthquake recurrence rate and interseismic coupling, collectively indicate an increased possibility of a near‐future rupture around the areas between the 2018 and 2020 events in Oaxaca. Furthermore, there is a lowered chance of shallow coastal or offshore normal earthquakes but an increased chance of inland normal ruptures.

Combined On-Fault and Off-Fault Paleoseismic Evidence in the Postglacial Infill of the Inner-Alpine Lake Achensee (Austria, Eastern Alps)

The Eastern European Alps are characterized by slow active deformation with low- to moderate seismicity. Recurrence rates of severe earthquakes exceed the time span of historical documentation. Therefore, historical and instrumental earthquake records might be insufficient for seismic hazard assessment and high-quality paleoseismic data is required. However, primary geological observations of postglacial fault activity are scarcely found, because major faults are buried below thick sedimentary sequences in glacially overdeepened valleys. Moreover, high erosion rates, gravitational slope processes and penetrative anthropogenic landscape modification often obscure geomorphic features related to surface ruptures. Here we present one of the rare paleoseismic data sets showing both on-fault evidence as subaqueous surface ruptures and off-fault evidence as multiple coeval mass-transport deposits (MTDs) and megaturbidites within a single high-resolution seismic-stratigraphic framework of the inner-alpine lake Achensee. Co-occurrence of on-fault and off-fault paleoseismic evidence on three stratigraphic levels indicates seismic activity with inferred moment magnitudes MW ∼6–6.5 of the local, lake-crossing Sulzgraben-Eben thrust at ∼8.3 ka BP and twice in Late Glacial times. Additional eight stratigraphic levels with only off-fault paleoseismic evidence document severe seismic shaking related to the historical MW ∼5.7 earthquake in Hall (CE 1670) and seven Holocene earthquakes, which have exceeded a local seismic intensity of ∼VI (EMS-98) at Achensee. Furthermore, we discuss natural and methodological influencing factors and potential pitfalls for the elaboration of a subaqueous paleoseismic record based on surface ruptures and multiple, coeval MTDs.

High resolution morphometric analysis of the Cordone del Vettore normal fault scarp (2016 central Italy seismic sequence): Insights into age, earthquake recurrence and throw rates

We investigated the late Quaternary throw distribution of the main normal fault that ruptured during the Mw 6.5 2016 earthquake in central Italy by means of a high-resolution structure-from-motion (SfM)-derived Digital Surface Model (DSM). We focused on a key area along the Cordone del Vettore fault (CDV), which is part of the Vettore-Bove fault system (VBFS). The CDV displays a prominent compound post-glacial scarp that allowed the reconstruction of the along-strike cumulative throw distribution. We propose a geometric approach to calculate the CDV fault throw distribution from the reconstruction of a displaced glaciation-related erosional surface, used as a geomorphic marker, and a series of closely spaced cross profiles. The proposed calculation accounts for both the slip vector direction and the degraded scarp top, including field data on fault dip angles. Following this approach, we recognized two scarps with a minimum average fault throw of ~21 m and ~35 m for this section of the investigated fault strand.The correlation with the possible post-LGM (Last Glacial Maximum) deglaciation phases of the erosional surface suggests a minimum scarp age of 25–27 ka cal BP. Such an age provides a reasonable CDV fault throw rate of ~0.8 mm/a, comparable with known long-term throw rates of the VBFS and active Apennines normal faults. By comparing the reconstructed long-term Cordone del Vettore throw distribution with the 2016 coseismic one, ~24 2016-like surface faulting events are required to generate the main cumulative scarp, under the assumption of constant slip per event. This, along with the age of the scarp, yields an average earthquake recurrence time interval of ~1100 a. These results suggest the presence of multiple regional markers that correlates with different LGM (if not pre-LGM) major glacial phases, whose erosional processes allow the preservation of pre-existing bedrock fault scarp remnants.

Probabilistic assessment and study of earthquake recurrence models for entire Northeast region of India

Northeast India is seismically most active region in India, and it falls under Zone V which represents the highest seismic risk in the country. This region has been experienced two great earthquakes like the 1897 Shillong (Mw 8.1) and the 1950 Assam earthquake (Mw 8.4) and several large earthquake (Mw ≥ 7) during last 122 years. Probabilistic approach and number statistical tools have been used by various researchers for finding the future earthquake recurrence rates. Using the earthquake catalogue, Gutenberg–Richter parameter has been estimated to evaluate seismic risk for six different regions: Eastern Himalayan, Indo-Burma region, Bengal Basin, Shillong Plateau, Mishmi Thrust, and Naga Thrust. Assuming that the earthquake occurrence is Poisson model, based on the obtained Gutenberg–Richter (G–R) relations, the probability of occurrence of earthquake of specified magnitude in given time is estimated for six seismotectonic regions. Further in this study, we made an attempt to estimate the probability of earthquake using four known statistical models, namely Exponential, Rayleigh, Weibull, and Pareto. The whole region is divided into six tectonic blocks to estimate the probability of an earthquake (Mw ≥ 5.5) through the maximization of conditional probability of earthquake occurrence. Time intervals for the occurrence of the next large earthquake in the six regions have been estimated by the maximization of conditional probability of earthquake occurrence. Pareto distribution shows the highest conditional probability compared to other distribution although it shows the lowest recurrence time compared to others. Rayleigh shows the lowest conditional probability, and Exponential shows intermediate probabilities in between Weibull and Pareto distributions. Specified four typical probability density models have been validated with the predicted event in Eastern Himalayan and Naga Thrust for earthquake Mw ≥ 5.5 recorded event.

Dynamics of the Seismic-Energy Structure on the Southwestern Flank of the Baikal Rift System: Andronov–Hopf Bifurcation

Abstract —The dynamics of the seismic-energy structure state on the southwestern flank of the Baikal rift system (BRS) has been analyzed at three hierarchical levels based on the annual cumulative data on the earthquakes with energy class KR ≥ 8 for the period 1964–2013. Changes in the state are characterized by three key parameters: maximum energy class Kmax, the slope of the earthquake recurrence curve γ, and seismic activity A10. With an increase in the earthquake recurrence intervals and the quantity of the earthquakes analyzed, the parameters reach their maxima reflecting the regularity of earth shocks classification by long periods. Two attractors are clearly distinguished in the phase pattern, where they reflect general quasi-stationarity (limit cycle) and local instability (focus) of the seismic-energy structure. The specifics of the attractor formation suggest a cycle birth bifurcation (Andronov–Hopf bifurcation). For a detailed analysis of the dynamics of seismic-energy structure formation, the slopes of the earthquake recurrence rate curves were calculated in the simulation scenarios of “aftershocks” and “swarm” earth shocks. Comparison of the simulated and real changes in the earthquake recurrence rate slopes shows a correspondence of the “aftershock” model to the dynamics of the seismic-energy structure of the lithosphere on the BRS southwestern flank.

Holocene mass movements in west and mid-Norwegian fjords and lakes

In this study, identified mass transport deposits (MTDs) in previously analyzed as well as new sediment cores and seismic profiles from 22 fjord systems and six lakes in west and mid-Norway are compiled in order to close knowledge gaps in the understanding of how mass movements relate to seismic activity and climatic changes affecting the sedimentary systems. A total of 125 postglacial MTDs have been identified and dated in the studied systems. Mass movement frequency plots suggest high mass movement activity for two periods in the Early Holocene (11,000–9700 and 8300–7700 cal. yrs BP), a quiescent period in the mid-Holocene, and a mass movement reactivation at ~4200 cal. yrs BP. The evaluation of trigger mechanisms makes us infer that some of the mass movements identified are most likely related to climatic processes and tsunamis. However, most of the events seem to be caused by regional seismic activity, resulting in failure of climatically-preconditioned slopes. We suggest that at least 36 individual regional earthquakes (M > 6) have occurred in west and mid-Norway through the Holocene. Earthquake recurrence rates of 1/80 years are estimated for the period directly after the last deglaciation (~12,800–11,600 cal. yrs BP), 1/200 years for the Early Holocene and 1/200 years for the last 4000 years of the Holocene time period. Comparisons with studies from other previously glaciated settings indicate that both Scandinavia and the Alps show similar trends as west and mid-Norway, but not Eastern Canada. This most likely reflects a later deglaciation of the Laurentide Ice Sheet.

Limit on slip rate and timing of recent seismic ground-ruptures on the Jinghong fault, SE of the eastern Himalayan syntaxis

Quantifying slip rates and earthquake occurrence of active faults on the Shan Plateau, southeast of the eastern Himalayan syntaxis, is critical to assessing the seismic hazard and understanding the kinematics and geodynamics of this region. Most previous estimates of slip rates are averaged over either many millions of years using offset geological markers or decades using GPS. Well-constrained millennial slip rates of these faults remain sparse and constraints on recurrence rates of damaging earthquakes exist only for a few faults. Here we investigate the millennial slip rate and timing of recent earthquakes on the Jinghong fault, one of the geomorphically most significant sinistral-slip faults on the central Shan Plateau. We map and reconstruct fault offset (18 ± 5 m) of alluvial fan features at Manpa on the central Jinghong fault, using a 0.1 m-resolution digital surface model obtained from an unmanned aerial vehicle survey. We establish a slip rate, ≤2.5 ± 0.7 mm/yr over the past ~7000 years, using pit-exposed stratigraphy. This millennial slip rate is consistent with rates averaged over both decadal and million-year timescales. Excavations at three sites near the town of Gelanghe on the northeastern Jinghong fault demonstrate 1) that the last seismic ground-rupture occurred between 482 and 889 cal yr BP, most likely in the narrower window 824–767 cal yr BP, if the lack of large earthquakes in the historical earthquake record is reliable, and 2) that multiple fault ruptures have occurred since ~3618 cal yr BP. Combining this finding with a lack of large earthquakes in the ~800-year-long Chinese historic record in this region, we suggest an average recurrence interval of seismic ground-ruptures on the order of ~1000 years. This recurrence interval is consistent with the slip rate of the Jinghong fault and the size and earthquake frequency on other sinistral faults on the Shan Plateau.

Sedimentary evidence of historical and prehistorical earthquakes along the Venta de Bravo Fault System, Acambay Graben (Central Mexico)

The Venta de Bravo normal fault is one of the longest structures in the intra-arc fault system of the Trans-Mexican Volcanic Belt. It defines, together with the Pastores Fault, the 80km long southern margin of the Acambay Graben. We focus on the westernmost segment of the Venta de Bravo Fault and provide new paleoseismological information, evaluate its earthquake history, and assess the related seismic hazard. We analyzed five trenches, distributed at three different sites, in which Holocene surface faulting offsets interbedded volcanoclastic, fluvio-lacustrine and colluvial deposits. Despite the lack of known historical destructive earthquakes along this fault, we found evidence of at least eight earthquakes during the late Quaternary. Our results indicate that this is one of the major seismic sources of the Acambay Graben, capable of producing by itself earthquakes with magnitudes (MW) up to 6.9, with a slip rate of 0.22–0.24mm yr−1 and a recurrence interval between 1940 and 2390years. In addition, a possible multi-fault rupture of the Venta de Bravo Fault together with other faults of the Acambay Graben could result in a MW>7 earthquake. These new slip rates, earthquake recurrence rates, and estimation of slips per event help advance our understanding of the seismic hazard posed by the Venta de Bravo Fault and provide new parameters for further hazard assessment.

Probabilistic tsunami hazard assessment along Oman coast from submarine earthquakes in the Makran subduction zone

The Sultanate of Oman is among the Indian Ocean countries that were subjected to at least two confirmed tsunamis during the twentieth and twenty-first centuries: the 1945 tsunami due to an earthquake in the Makran subduction zone in the Sea of Oman (near-regional field tsunami) and the Indian Ocean tsunami in 2004, caused by an earthquake from the Andaman Sumatra subduction zone (far - field tsunami). In this paper, we present a probabilistic tsunami hazard assessment for the entire coast of Oman from tectonic sources generated along the Makran subduction zone. The tsunami hazard is assessed taking into account the contribution of small- and large-event magnitudes. Results of the earthquake recurrence rate studies and the tsunami numerical modeling for different magnitudes were used through a logic-tree to estimate the tsunami hazard probabilities. We derive probability hazard exceedance maps for the Omani coast considering the exposure times of 100, 250, 500, and 1000 years. The hazard maps consist of computing the likelihood that tsunami waves exceed a specific amplitude. We find that the probability that a maximum wave amplitude exceeds 1 m somewhere along the coast of Oman reaches, respectively, 0.7 and 0.85 for 100 and 250 exposure times, and it is up to 1 for 500 and 1000 years of exposure times. These probability values decrease significantly toward the southern coast of Oman where the tsunami impact, from the earthquakes generated at Makran subduction zone, is low.

Bayesian probabilities of earthquake occurrences in Longmenshan fault system (China)

China has a long history of earthquake records, and the Longmenshan fault system (LFS) is a famous earthquake zone. We believed that the LFS could be divided into three seismogenic zones (north, central, and south zones) based on the geological structures and the earthquake catalog. We applied the Bayesian probability method using extreme-value distribution of earthquake occurrences to estimate the seismic hazard in the LFS. The seismic moment, slip rate, earthquake recurrence rate, and magnitude were considered as the basic parameters for computing the Bayesian prior estimates of the seismicity. These estimates were then updated in terms of Bayes’ theorem and historical estimates of seismicity in the LFS. Generally speaking, the north zone seemingly is quite peaceful compared with the central and south zones. The central zone is the most dangerous; however, the periodicity of earthquake occurrences for M s = 8.0 is quite long (1,250 to 5,000 years). The selection of upper bound probable magnitude influences the result, and the upper bound magnitude of the south zone maybe 7.5. We obtained the empirical relationship of magnitude conversion for M s and ML, the values of the magnitude of completeness Mc (3.5), and the Gutenberg–Richter b value before applying the Bayesian extreme-value distribution of earthquake occurrences method.

Uncertainty in recurrence rates of large magnitude events due to short historic catalogs

Seismic hazard analysis requires knowledge of the recurrence rates of large magnitude earthquakes that drive the hazard at low probabilities of interest for seismic design. Earthquake recurrence is usually determined through studies of the historic earthquake catalogue for a given region. Reliable historic catalogues generally span time periods of 100–200 years in North America, while large magnitude events (M ≥ 7) have recurrence rates on the order of hundreds or thousands of years in many areas, resulting in large uncertainty in recurrence rates for large events. Using Monte Carlo techniques and assuming typical recurrence parameters, we simulate earthquake catalogues that span long periods of time. We then split these catalogues into smaller catalogues spanning 100–200 years that mimic the length of historic catalogues. For each of these simulated “historic” catalogues, a recurrence rate for large magnitude events is determined. By comparing recurrence rates from one historic-length catalogue to another, we quantify the uncertainty associated with determining recurrence rates from short historic catalogues. The use of simulations to explore the uncertainty (rather than analytical solutions) allows us flexibility to consider issues such as the relative contributions of aleatory versus epistemic uncertainty, and the influence of fitting method, as well as lending insight into extreme-event statistics. The uncertainty in recurrence rates of large (M > 7) events is about a factor of two in regions of high seismicity, due to the shortness of historic catalogues. This uncertainty increases greatly with decreasing seismic activity. Uncertainty is dependent on the length of the catalogue as well as the fitting method used (least squares vs. maximum likelihood). Examination of 90th percentile recurrence rates reveals that epistemic uncertainty in the true parameters may cause recurrence rates determined from historic catalogues to be uncertain by a factor greater than 50.

Bayesian probabilities of earthquake occurrences in Shanxi rift system (China)

China has a long history of earthquake records. The Shanxi rift system (SRS) is situated along the axial zone of the domal uplift of the Shanxi Highlands and is the boundary between the Ordos block and the North China Plain block. Strong earthquakes in the SRS have been recorded since the thirteenth century. In our work, we applied the Bayesian probability method using extreme value distribution of earthquake occurrences to estimate the seismic hazard in the SRS. The seismic moment, slip rate, earthquake recurrence rate, and magnitude were considered as the basic parameters for computing the Bayesian prior estimates of the seismicity. These estimates were then updated in terms of Bayes’ theorem and historical estimates of seismicity in the SRS. The probability of occurrence of $$M_{\text{s}} = 5.0$$ for Z1, Z2, and Z3 is less than 0.3, 0.1, and 0.6, respectively (T = 5 years). The probability of the occurrence of M $$\ge$$ 8.0 is small for the whole SRS. The selection of upper bound magnitude probably influences the result, and the upper bound magnitude of Z1, Z2, and Z3 may be 7.5, 7.0, and 8.5, respectively. We obtained the values of the magnitude of completeness M c (3.2) and the Gutenberg–Richter b value before applying the Bayesian extreme value distribution of earthquake occurrences method.

Lake sediments as natural seismographs: A compiled record of Late Quaternary earthquakes in Central Switzerland and its implication for Alpine deformation

AbstractCentral Switzerland lies tectonically in an intraplate area and recurrence rates of strong earthquakes exceed the time span covered by historic chronicles. However, many lakes are present in the area that act as natural seismographs: their continuous, datable and high‐resolution sediment succession allows extension of the earthquake catalogue to pre‐historic times. This study reviews and compiles available data sets and results from more than 10 years of lacustrine palaeoseismological research in lakes of northern and Central Switzerland. The concept of using lacustrine mass‐movement event stratigraphy to identify palaeo‐earthquakes is showcased by presenting new data and results from Lake Zurich. The Late Glacial to Holocene mass‐movement units in this lake document a complex history of varying tectonic and environmental impacts. Results include sedimentary evidence of three major and three minor, simultaneously triggered basin‐wide lateral slope failure events interpreted as the fingerprints of palaeoseismic activity. A refined earthquake catalogue, which includes results from previous lake studies, reveals a non‐uniform temporal distribution of earthquakes in northern and Central Switzerland. A higher frequency of earthquakes in the Late Glacial and Late Holocene period documents two different phases of neotectonic activity; they are interpreted to be related to isostatic post‐glacial rebound and relatively recent (re‐)activation of seismogenic zones, respectively. Magnitudes and epicentre reconstructions for the largest identified earthquakes provide evidence for two possible earthquake sources: (i) a source area in the region of the Alpine or Sub‐Alpine Front due to release of accumulated north‐west/south‐east compressional stress related to an active basal thrust beneath the Aar massif; and (ii) a source area beneath the Alpine foreland due to reactivation of deep‐seated strike‐slip faults. Such activity has been repeatedly observed instrumentally, for example, during the most recent magnitude 4·2 and 3·5 earthquakes of February 2012, near Zug. The combined lacustrine record from northern and Central Switzerland indicates that at least one of these potential sources has been capable of producing magnitude 6·2 to 6·7 events in the past.

Truthfulness of the Existence of the Pelusium Megashear Fault System, East of Cairo, Egypt

The so-called Pelusium Megashear System (PMS), consists of echelon left-lateral megashears crossing Africa from the Nile-Delta since the Precambrian times. Although this system is questioned by some scientists, its existence is sup- ported by others. This research work provides evidences for the existence of the PMS near Egypt’s capital (Cairo city). Evidence is interpreted from gravity, magnetic, and seismological data, which proves that it has been in existence since 2800 BC [1]. To support the existence of this fault zone system, all available tectonic data are reviewed; new magnetic tilt derivative TDR map and recent fault plane solution map are introduced. Moreover available earthquake catalogue for historical and recent occurrences in and around the Pelusium zone is compiled. The collected recent and historical seismicity data is supporting the existence of PMS system. The faults excluded from magnetic maps were found to be in a good agreement with tectonic and gravity data introduced by some authors. Available fault plane solutions for old and recent earthquakes gave rise to the hypothesis that the PMS is right lateral shear system. Additionally, the Pelusium zone is evaluated for the rate of seismic activity. The hazards of these zones are studied by calculating the earthquake recurrence rates using Richter-Gutenberg formula (LogN = a – bM). A statistical method is applied to exclude the effect of lack of data due to little seismograph station in the early records, or lack of population density. The Pelusium Megashear fault system proved to be active at least in Egypt, however, it plays a role only over big time window, may be thousands of years to dissipate stresses accumulated within the west of Sinai Peninsula in the African Eurasian-Arabian plates. Finally integrated tectonic model including the effect of PMS is introduced to solve the complexity of intraplate tectonics in Northern Egypt.

Effects from the Wenchuan Earthquake and seismic hazard in the Longmenshan Mountains at the eastern margin of the Tibetan Plateau

Effects from the disastrous Ms 8.0 Wenchuan Earthquake of May 12, 2008 show that the seismic hazard is closely related to the proximity of active faults and elevated areas of unstable rock as well as the recurrence rate of large earthquakes. Dextral-slip thrusting in the Longmenshan Mountains formed large displacement along ~250km of the Central Longmenshan Fault and smaller offsets along sub-parallel faults. The distribution pattern of the major destruction has a strong northeast–southwest orientation closely related to the ruptured faults and decreases noticeably 3–5km away from the Central Longmenshan Fault and ~2km from the other faults. Thousands of landslides, rock falls and debris flows triggered by the earthquake lie chiefly adjacent to the principal fault, and smaller-scale landslides along the other faults as well as in distant areas. Some landslides formed dams whose impounded waters threatened downstream cities. Future landslides, rock falls and debris flows will result from rock loosened by the earthquake during rainy seasons or subsequent earthquakes.The Central Longmenshan Fault had maximum displacements of 4.6m dip-slip and 6.1m dextral-slip and the total dip and dextral-slip displacement for all faults is 5.9m and 7.0m, respectively. These faults apparently converge at depth and account for the crustal shortening in the region. Their displacements coupled with convergence rates determined by GPS measurements provide an estimated recurrence interval for an Ms 8.0 earthquake along the Central Longmenshan Fault of between 4600 and 6600years and that for the entire Longmenshan Mountains between 1000 and 3000years.

Moment Magnitude (Mw) Conversion Relations for Use in Hazard Assessment in Eastern Canada

To be unbiased and uniform across a wide geographical area, seismic hazard assessments based primarily on earthquake recurrence rates require that the same magnitude scale be used for all earthquakes evaluated. Increasingly, moment magnitude, M W , is seen as the magnitude of preference. Moment magnitude, however, was not routinely calculated in the past for earthquakes in Canada, necessitating the conversion from other magnitude types in common use. This step is complicated by the fact that several magnitude scales are routinely reported for Canadian earthquakes with the choice being influenced primarily by geography and to a lesser extent by the size of the earthquake. This paper focuses on eastern Canada, where m N is the most commonly used magnitude scale. Conversions to M W are established and evaluated. The simple conversion of applying a constant is sufficient. However, the conversion is time dependent with the constant changing from 0.41 to 0.53 in the mid-1990s.