Instrumental Seismic Data Research Articles

Application of the EEPAS earthquake forecasting model to Italy

SUMMARY The Every Earthquake a Precursor According to Scale (EEPAS) forecasting model is a space–time point-process model based on the precursory scale increase ($\psi $ ) phenomenon and associated predictive scaling relations. It has been previously applied to New Zealand, California and Japan earthquakes with target magnitude thresholds varying from about 5–7. In all previous application, computations were done using the computer code implemented in Fortran language by the model authors. In this work, we applied it to Italy using a suite of computing codes completely rewritten in Matlab. We first compared the two software codes to ensure the convergence and adequate coincidence between the estimated model parameters for a simple region capable of being analysed by both software codes. Then, using the rewritten codes, we optimized the parameters for a different and more complex polygon of analysis using the Homogenized Instrumental Seismic Catalogue data from 1990 to 2011. We then perform a pseudo-prospective forecasting experiment of Italian earthquakes from 2012 to 2021 with Mw ≥ 5.0 and compare the forecasting skill of EEPAS with those obtained by other time independent (Spatially Uniform Poisson, Spatially Variable Poisson and PPE: Proximity to Past Earthquakes) and time dependent [Epidemic Type Aftershock Sequence (ETAS)] forecasting models using the information gain per active cell. The preference goes to the ETAS model for short time intervals (3 months) and to the EEPAS model for longer time intervals (6 months to 10 yr).

DevelNet: Earthquake Detection on Develocorder Films with Deep Learning: Application to the Rangely Earthquake Control Experiment

Abstract There exists over a century of instrumental seismic data; however, most seismograms recorded before the 1980s are only available in analog form. Although analog seismograms are of great value, they are underutilized due to the difficulties of making quantitative measurements on the original media and in converting them to digital time series. In this study, we present an alternative workflow, based on deep learning, to reconstruct an earthquake catalog from images of analog data without conversion to vector time series. We trained a convolutional neural network—DevelNet, using synthetic analog data to detect earthquakes on scanned multichannel Develocorder film images. We then developed an image-based processing workflow to measure arrival times, locate, and determine the magnitudes of earthquakes in the data. We demonstrate the performance of this approach on two years of continuous Develocorder film recordings from the Rangely earthquake control experiment in the mid-1970s. Our approach detects twice the number of events reported in the original catalog (Raleigh et al., 1976). This demonstrates that DevelNet efficiently detects earthquakes from Develocorder film scans, performs consistently over time, and is robust to changes in network geometry. Our locations generally agree with the original study, although the automatically measured arrival times are less precise than manual reading, leading to increased location scatter. Our automatic workflow of Develocorder films rivals the performance of skilled analysts in earthquake detection, but with minimal human intervention. This image-based processing offers a new approach for effectively and efficiently extracting earthquake information from analog seismic data.

لرزه زمین ساخت پهنه های البرز خاوری و کپه داغ با استفاده از داده های شبکه لرزه نگاری محلی

The Kopeh Dagh and Binalud-Alla Dagh mountains are important structural elements located in the northeastern boundary of Arabia-Eurasia collision zone. Due to existence of large cities with a long history of civilization, there is a relatively rich body of data on historical seismicity in this area. Nonetheless, little adequate instrumental seismic data were available prior to this study. In this paper, we utilized the temporary China-Iran local seismic network data deployed in the area for 13 months. Based on this data, we determined 37 focal solutions through first motion polarity approach suggesting a combination of strike-slip, reverse and normal mechanisms. There is a significant concentration of epicenters and focal mechanisms around the eastern Alborz - Kopeh Dagh boundary along the Atrak River. The southern and western boundaries of the Binalud Mountains also show relatively high seismic activities. The Local magnitude (ML) of the events ranges from 3.5 to 4.9 with depths of up to 20 km, mostly concentrated at ~10 km. The principal stress axes and slip vectors obtained from the focal mechanisms agree well with kinematic state of main faults and tectonic regime of the area, confirming the seismogenic nature of these faults. In addition, they are consistent with right-lateral component of slip along thrust faults in eastern Kopeh Dagh and Binalud and both laft- and right-lateral motions in the central Kopeh Dagh.

Revisiting California’s Past Great Earthquakes and Long-Term Earthquake Rate

ABSTRACTIn this study, we revisit the three largest historical earthquakes in California—the 1857 Fort Tejon, 1872 Owens Valley, and 1906 San Francisco earthquakes—to review their published moment magnitudes, and compare their estimated shaking distributions with predictions using modern ground-motion models (GMMs) and ground-motion intensity conversion equations. Currently accepted moment magnitude estimates for the three earthquakes are 7.9, 7.6, and 7.8, respectively. We first consider the extent to which the intensity distributions of all three earthquakes are consistent with a moment magnitude toward the upper end of the estimated range. We then apply a GMM-based method to estimate the magnitudes of large historical earthquakes. The intensity distribution of the 1857 earthquake is too sparse to provide a strong constraint on magnitude. For the 1872 earthquake, consideration of all available constraints suggests that it was a high stress-drop event, with a magnitude on the higher end of the range implied by scaling relationships, that is, higher than moment magnitude 7.6. For the 1906 earthquake, based on our analysis of regional intensities and the detailed intensity distribution in San Francisco, along with other available constraints, we estimate a preferred moment magnitude of 7.9, consistent with the published estimate based on geodetic and instrumental seismic data. These results suggest that, although there can be a tendency for historical earthquake magnitudes to be overestimated, the accepted catalog magnitudes of California’s largest historical earthquakes could be too low. Given the uncertainties of the magnitude estimates, the seismic moment release rate between 1850 and 2019 could have been either higher or lower than the average over millennial time scales. It is further not possible to reject the hypothesis that California seismicity is described by an untruncated Gutenberg–Richter distribution with a b-value of 1.0 for moment magnitudes up to 8.0.

Historical and Modern Seismicity of the Semipalatinsk Test Site

According to the current maps of general seismic zoning of the Republic of Kazakhstan (2006), the territory of the Semipalatinsk Test Site (STS) is considered an aseismic region. However, recent investigations and an analysis of archived data have shown that the Test Site territory and its vicinity have experienced and still experience tectonic and induced earthquakes. The maximum magnitude of recorded earthquakes is 5–5.9. An analysis of global seismological bulletins and data on historical seismicity from literature sources is performed to solve the problem of seismicity in the STS region. Historic analog seismograms of earthquakes have been collected since 1925; the earthquake parameters are estimated more precisely. Modern instrumental seismic data of the Kazakhstan monitoring network since 1994 are processed, as is the data of temporary networks of seismic stations operating on the territory of the test site in 2005–2010 in the region of the Sary-Uzen, Balapan, and Degelen test sites. These works resulted in the creation of a common earthquake catalogue for the STS territory and its vicinity from 1783 up to the present. Macroseismic data of the felt earthquakes have been collected; strong motion records have been analyzed. Deep faults dividing Earth’s crust blocks have been marked out. Tectonic elements are located by decoding the Landsat space images and using materials of geologic and topographic surveys. The calculations show that the STS territory can experience events with intensity 6 based on the MSK-64 scale.

Geological assessment of the Neom mega-project area, northwestern Saudi Arabia: an integrated approach

The Neom mega-project area is located on the northwestern Arabian Plate and is associated with the Red Sea divergence and the Gulf of Aqaba-Dead Sea transform boundary. The study area is controlled by numerous major regional tectonic features including the Red Sea, Gulf of Suez, the Gulf of Aqaba-Dead Sea fault system, and a large number of recorded earthquakes. Evaluation of the tectonic framework of the Neom mega-project is important because of its economic and developmental significance. Here, geological, geophysical, field investigation, and seismological data were integrated to achieve these aims. The sinistral strike-slip regime of the study area involves extensional structures including normal faults and horizontal shear zones of vertical planes. In the Aqaba-Dead Sea faults, the left-lateral transform fault system is sharply expressed along the Wadi courses cutting into Proterozoic igneous and metamorphic rocks. The historical and instrumental seismicity data collected and processed illustrates a good association with the general tectonic trends affecting the Neom area. Moreover, the Gulf of Aqaba region remains the most active seismotectonic source zone affecting northwest Saudi Arabia and the Gulf of Aqaba region, with three big earthquake swarms recorded in 1983, 1993, and 1995.

Post-earthquake warning for Vrancea seismic source based on code spectral acceleration exceedance

Post-earthquake crisis management is a key capability for a country to be able to recover after a major seismic event. Instrumental seismic data transmitted and processed in a very short time can contribute to better management of the emergency and can give insights on the earthquake`s impact on a specific area. Romania is a country with a high seismic hazard, mostly due to the Vrancea intermediate-depth earthquakes. The elastic acceleration response spectrum of a seismic motion provides important information on the level of maximum acceleration the buildings were subjected to. Based on new data analysis and knowledge advancements, the acceleration elastic response spectrum for horizontal ground components recommended by the Romanian seismic codes has been evolving over the last six decades. This study aims to propose a framework for post-earthquake warning based on code spectrum exceedances. A comprehensive background analysis was undertaken using strong motion data from previous earthquakes corroborated with observational damage, to prove the method`s applicability. Moreover, a case-study for two densely populated Romanian cities (Focsani and Bucharest) is presented, using data from a 5.5 MW earthquake (October 28, 2018) and considering the evolution of the three generations of code-based spectral levels for the two cities. Data recorded in free-field and in buildings were analyzed and has confirmed that no structural damage occurred within the two cities. For future strong seismic events, this tool can provide useful information on the effect of the earthquake on structures in the most exposed areas.

Seismotectonics of South Africa

Assessment of seismic hazard is challenging especially for low seismicity regions like southern Africa. There is very little knowledge in terms of the coupling between the seismicity and active faults leading to an incomplete dataset in terms of recurrence times and seismic zonation. Concerted efforts have been made to compile a seismotectonic map of South Africa that will assist in delineating seismic hotspots in order to carry out a proper seismic hazard assessment using state of the art methodologies. In preparing the map, a homogeneous earthquake catalogue was compiled from local, regional and international databases. Fault plane solutions and stress information were obtained from publications, reports and international organisations such as the ISC, USGS and Harvard CMT. Though few such data are available for South Africa, all collected information is vital in the effort to understand the tectonics and stress modelling of the region. Several faults have been identified as possibly active, though some of them have no significant seismicity associated with them. Through these efforts, a seismotectonic map of South Africa has now been prepared. It is hoped that the information in the seismotectonic map will contribute to the preparation of more accurate hazard assessments for South Africa. However, efforts continue to collect and improve collection methods of historical and instrumental seismicity data, as well as geological information to improve the available seismotectonic data for this region.

Numerical DEM simulation of AE in plate fracture and analogy with the frequency of seismic events in SCRs

The present paper examines, by Monte Carlo simulation employing the Discrete Element Method (DEM), the occurrence of micro-fractures and the evolution of damage, as cracks coalesce in large fractures, in a plate subjected to increasing stress. Numerical simulations results which in previous studies predicted successfully acoustic emission (AE) in laboratory samples, are compatible with the conclusions of the assessment of instrumental data in a Stable Continental Regions (SCR). The locations of AE sources, correlated with the growth of a diagonal fracture in the plate, are numerically determined. Seismic activity, on the other hand, is higher along inter-plate boundaries, decreasing in intra-plate regions (SCR) where it's prediction for engineering purposes presents great difficulties. The authors examined, in previous papers, instrumental seismic data for a 1200 km square region in the South American SCR, showing that the distribution of amplitudes is not exponential, as implicitly assumed in the Gutenberg-Richter law, and also that the largest events do not occur according to the distribution of small events. These contentions are also applicable to the numerical simulations described in the paper, illustrating similarity between the distributions of simulated AE events in the plate and seismic activity within a SCR.

GPS measurements of crustal deformation across the southern Arava Valley section of the Dead Sea Fault and implications to regional seismic hazard assessment

Detailed analysis of crustal deformation along the southern Arava Valley section of the Dead Sea Fault is presented. Using dense GPS measurements we obtain the velocities of new near- and far-field campaign stations across the fault. We find that this section is locked with a locking depth of 19.9 ± 7.7 km and a slip rate of 5.0 ± 0.8 mm/yr. The geodetically determined locking depth is found to be highly consistent with the thickness of the seismogenic zone in this region. Analysis of instrumental seismic record suggests that only ~1% of the total seismic moment accumulated since the last large event occurred about 800 years ago, was released by small to moderate earthquakes. Historical and paleo-seismic catalogs of this region together with instrumental seismic data and calculations of Coulomb stress changes induced by the 1995 Mw 7.2 Nuweiba earthquake suggest that the southern Arava Valley section of the Dead Sea Fault is in the late stage of the current interseismic period.

The instrumental seismicity of the Jordan Dead Sea transform

The instrumental seismicity that occurred in the Jordan Dead Sea transform region during the period 1900–2014 is compiled from all available sources. Some 492 phosphate mining explosions (M ≤ 3.9) are recognized and filtered from the data. Excluding these, it is found that 4448 earthquakes have occurred with magnitudes M ≥ 3.0. Only 572, 18 and 2 of these had magnitudes M ≥ 4, 5, and 6 in respective order. Average recurrence periods for the 5 and 6 magnitudes are 6.3 and 57 years. Much of these have occurred in sequences and swarms. The epicentral distribution of the compiled instrumental seismicity data shows very good correlation with the general tectonics of the study region. All tectonic elements are active in the present with a noticeable hazard. The regional strike-slip faults of the transform proper remain the major sources of this hazard. They account for not less than 99% of the seismic energy released from all instrumental data. The calculated a-parameter of the whole transform is 6.6. It varies for all its strike-slip faults mostly in the range 6.0–6.6. The b-value of the whole transform and some of its major segments is 1.0. Others show b-variations in the range of 1.1–1.3. Such a- and b-values imply recurrence periods of 38 years and 395 years for the 6 and 7 magnitude earthquakes. Such values, their variations and the seismic moment calculations clearly indicate an appreciable level of seismic hazard associated with all segments. This hazard appears to be highest for Al Ghab segment, followed by Beqa’a and Wadi Araba segments, respectively. The other three segments appear to be of lower hazard. The seismicity of this region is very shallow. More than 99% of the seismic energy has been released from the brittle granitic upper crust whose thickness is about 21 km and its Poisson’s ratio is 0.25. More than 93.6% of the energy was released from its upper 10 km. Very little energy is released from the underlying ductile basaltic crust whose Poisson’s ratio is 0.29. The calculated seismic slip rate along the Whole Jordan Dead Sea transform is 0.54 cm/year if the fault depth is assumed 10 km. It increases to 0.77 and 1.07 cm/year if the fault depth is reduced to 7 and 5 km, respectively. These slip rates are comparable with the long-term geologically deduced rate of 1 cm/year.

On unknown strong Holocene earthquakes in the south of the Issyk Kul depression, Tien Shan

An area of paleoseismic deformations of seismogravitation and seismotectonic genesis that trace the epicentral zones of ancient earthquakes, is revealed for the first time in the Tossor river basin, the southern Issyk Kul region. The C14 age is the 9th century AD for the recent earthquake and middle-early Holocene for the earlier seismic event. High seismic activity of the Pre-Terskey Border Fault in the south of the Issyk Kul Lake depression is recorded. An upslope-facing scarp and many significant rockslides in the Tossor river basin mark an epicentral zone of strong Holocene earthquakes, which is not consistent with instrumental seismic data and was not taken into account when compiling the latest seismic zoning map of the Kyrgyz Republic.

Seismicity and seismotectonics of the Red Sea Region

The historical seismicity of the Red Sea region between latitudes 13 and 30° N and longitudes 32 and 46° E has been revised. It is found that during the last 1400 years, some 88 historical earthquakes have occurred with magnitudes M ≥ 5.6. Only two M = 7.0 are reported, one in each of the northern and southern Red Sea regions, followed by two and one 6.8 in the northern and southern regions, respectively. During the period 1960–2010, some 1310 instrumental earthquakes have occurred in the region with M ≥ 4.0. The largest (M = 7.1) occurred in the Gulf of Aqaba, followed by a 6.9 in the entrance of the Gulf of Suez, followed by a 6.7 and a 6.4 that occurred in the southern Red Sea region. All others had M ≤ 6.2. More than 90 % of the seismicity has occurred in the form of sequences and swarms and are believed to be volcanic related. Thus, the seismic hazard of the study region remains quite limited. Both northern and southern parts of the Red Sea region are of comparable seismic activities, while that of the central part is of lower activity. The historical and instrumental seismicity data show excellent correlation with the general tectonics of the study region. These also show that earthquake activity has fluctuated with time from one region to the other. In the Red Sea proper, more than 83 % of the seismic moment is associated with the regional faults of the axial trough with noticeable concentration of activity where the NE trending strike-slip faults cross this trough. Published fault plane solutions for the largest instrumental earthquakes of the last few decades show that both normal and strike-slip faults are active in support of a divergent environment between the Arabian and African plates. Shallow seismicity is a characteristic feature of this region. The data indicates that lithospheric deformations beneath the gulfs area are restricted to the upper part of the crust, while beneath the Red Sea south of latitude 27.8°, these appear to concentrate partially within the crust down to 10 km depth and much more within the uppermost mantle, mostly from 20.1 to 40 km depths. Very little earthquakes occur at depths deeper than 60 km. Frequency-magnitude results of both historic and instrumental data gave the expected b value close to 1.0. The calculated recurrence periods for earthquakes with M = 6, 6.5 and 7 are 30 ± 2 years, 150 ± 10 years and 600 ± 20 years, respectively. The data show that the threshold magnitude for the study region is 4.0, and slightly more for the axial trough.

Reconstructing the Kolka surge on September 20, 2002 from the instrumental seismic data

The process of the Kolka rock and ice avalanche on September 20, 2002 in the Karmadon Gorge, North Ossetia is reconstructed based on analyzing the instrumental seismic records. The results of calculating the velocities of the rock-ice mass movement on the interval from the Maili Glacier to the Karmadon Gate agree with the results of mathematical modeling the avalanche flow in a gorge. The macroseismic effect of the surge impact on the rocks in the region of the Karmadon Gate is investigated from seismic data and the results of surveying the territory carried out by the authors in 2003–2004.

Evidences of a lithospheric fault zone in the Sicily Channel continental rift (southern Italy) from instrumental seismicity data

Sicily Channel is a portion of Mediterranean Sea, between Sicily (Southern Italy) and Tunisia, representing a part of the foreland Apennine-Maghrebian thrust belt. The seismicity of the region is commonly associated with the normal faulting related to the rifting process and volcanic activity of the region. However, certain seismic patterns suggest the existence of some mechanism coexisting with the rifting process. In this work, we present the results of a statistical analysis of the instrumental seismicity and a reliable relocalization of the events recorded in the last 30 yr in the Sicily Channel and western Sicily using the Double Difference method and 3-D Vp and Vs tomographic models. Our procedure allows us to discern the seismic regime of the Sicily sea from the Tyrrhenian one and to describe the main features of an active fault zone in the study area that could not be related to the rifting process. We report that most of the events are highly clustered in the region between 12.5°–13.5°E and 35.5°–37°N with hypocentral depth of 5–40 km, and reaching 70 km depth in the southernmost sector. The alignment of the seismic clusters, the distribution of volcanic and geothermal regions and the location of some large events occurred in the last century suggest the existence of a subvertical shear zone extending for least 250 km and oriented approximately NNE–SSW. The spatial distribution of the seismic moment suggests that this transfer fault zone is seismically discontinuous showing large seismic gaps in proximity of the Ferdinandea Island, and Graham and Nameless Bank.

Seismic Hazard Analysis and Obtaining Uniform Hazard Spectra for Esfahan Region, Iran

The present study was conducted to determine peak ground acceleration (PGA) over bedrock in probabilistic analysis methods for the seismic hazard and uniform hazard spectra at different hazard levels for Esfahan city. A series of statistics containing historical and instrumental seismic data covering from the 8th century A.D. to the now up to a radius of 200 km was employed and seismic sources were modeled up to a radius of 200 km from Esfahan city. For this purpose the method proposed by Kijko (2000) was employed considering uncertainty in magnitude and incomplete earthquake catalogue. Seismic hazard analysis is then carried out for Esfahan city by using SEISRlSK III (Bender and Perkins, 1987) program for 11×13 grid points. Four different attenuation relationships of PGA and SA with logic tree were used to determine the PGA on bedrock. The PGA can be determined for 143 points and the hazard spectra can be specified for 20 points of the city. Covering %2 and %10 probability of exceedance in one life cycle of 50 years are presented. Finally, the uniform hazard spectra was also presented with %10 and %2 of probability of exceedance in one life cycles of 50 years are presented along with New Mark and Hall Spectra.

The Greek Database of Seismogenic Sources (GreDaSS): state-of-the-art for northern Greece

The Greek Database of Seismogenic Sources (GreDaSS) is a repository of geological, tectonic and active-fault data for the Greek territory and its surroundings. In this report, we present the state-of-the-art of an on-going project devoted to the building of the GreDaSS, which represents the results of decades of investigations by the authors and a myriad of other researchers working on the active tectonics of the broader Aegean Region. The principal aim of this international project is to create a homogeneous framework of all of the data relevant to the seismotectonics, and especially the seismic hazard assessment, of Greece and its surroundings, as well as to provide a common research platform for performing seismic hazard analyses, modeling and scenarios from specific seismogenic structures. In particular, we introduce and synthetically describe the results obtained (and included in the database) to date in the northern sector of continental Greece and the Aegean Sea. As a first step we collected all available (both published and unpublished) historical and instrumental seismicity data relevant to the determining of the causative faults. Following the experience of recent 'surprising' earthquakes (e.g. 1995 Kozani, and 1999 Athens), we realized the deficiency of such an approach, and decided to also include in the GreDaSS active faults (i.e. seismogenic sources) recognized on the basis of geological, structural, morphotectonic, paleoseismological and geophysical investigations. A second step is the critical analysis of all of the collected data for the extraction of the necessary seismotectonic information, enabling the recognition of as many seismogenic sources as possible, as well as their characterization and parameterization. The most updated version of the database consists of numerous seismogenic sources that are categorized into three types: composite, individual, and debated. In this report, we describe the major seismotectonic properties of all of the composite seismogenic sources and individual seismogenic sources in northern Greece, which imply the partitioning of the area into five sectors that show similar internal behavior. Northern Greece was chosen as a pilot area because the parameters and accompanied metadata of its seismogenic sources show a high level of confidence and completeness. The amount of information and the degree of uncertainty is different for the three types.

Evaluation of earthquake activity along the Serghaya fault, Syria, from instrumental seismic data

This is a tentative study in order to characterize and identify the Serghaya fault in Syria through an analysis of its instrumentally observed earthquake activity for the period of 1995–2009. Different approaches are used to evaluate a- and b-values of the Gutenberg-Richter relation. It has been found that the computed b-values (around 1.5) are bigger than usually expected, which could be related either to incompleteness of earthquake catalogue or to invalidity of the Gutenberg-Richter model in the case of Serghaya fault. Based on several explanations of high b-values, existing in the literature, it can be inferred that the events recorded on the Serghaya fault occurred at small depths in the heterogeneous milieus under low stresses. A relative seismic quiescence from 1900 up to now is observed, whereas the biggest earthquake recorded during the study period does not exceed magnitude 3.9. Such quiescence does not reflect accurately an earthquake potential of the Serghaya fault and can probably indicate a large-magnitude earthquake occurrence in near future. The established earthquake catalogue must be necessarily completed in order to deeper characterize the real behavior of the Serghaya fault. Such a characterization, accompanied with seismic activity evaluation, could be used in the assessment of seismic hazard.

A study on seismicity and seismic hazard for Karnataka State

This paper presents a detailed study on the seismic pattern of the state of Karnataka and also quantifies the seismic hazard for the entire state. In the present work, historical and instrumental seismicity data for Karnataka (within 300 km from Karnataka political boundary) were compiled and hazard analysis was done based on this data. Geographically, Karnataka forms a part of peninsular India which is tectonically identified as an intraplate region of Indian plate. Due to the convergent movement of the Indian plate with the Eurasian plate, movements are occurring along major intraplate faults resulting in seismic activity of the region and hence the hazard assessment of this region is very important. Apart from referring to seismotectonic atlas for identifying faults and fractures, major lineaments in the study area were also mapped using satellite data. The earthquake events reported by various national and international agencies were collected until 2009. Declustering of earthquake events was done to remove foreshocks and aftershocks. Seismic hazard analysis was done for the state of Karnataka using both deterministic and probabilistic approaches incorporating logic tree methodology. The peak ground acceleration (PGA) at rock level was evaluated for the entire state considering a grid size of 0.05A degrees x 0.05A degrees. The attenuation relations proposed for stable continental shield region were used in evaluating the seismic hazard with appropriate weightage factors. Response spectra at rock level for important Tier II cities and Bangalore were evaluated. The contour maps showing the spatial variation of PGA values at bedrock are presented in this work.

Neotectonic extrusion of the Eastern Alps: Constraints from U/Th dating of tectonically damaged speleothems

We suggest that the Salzachtal-Ennstal-Mariazell-Puchberg (SEMP) fault, a major strike-slip system in the European Alps, is active. It has accommodated lateral extrusion of the central part of the Eastern Alps toward the Pannonian Basin. The main tectonic activity of this fault dates back to Oligocene and Miocene time, but until now it was largely unknown whether the fault was still active. We present here the first field evidence of neotectonic activity from a cave in the Hochschwab karst massif (Styria, Austria) that intersects a segment of the SEMP fault zone. Damaged speleothems in this cave include scratched flowstone (a hitherto undescribed feature), massive flowstone disrupted by a fault, and ruptured flowstone. The superposition of younger flowstone layers allows constraining the time frame of the tectonic events using U/Th dating. The youngest flowstone of the pre-damage generation is ca. 118 ka (end of the Last Interglacial) and the oldest post-event layer is ca. 9 ka (early Holocene). The tectonic event bracketed by these layers coincided with a growth hiatus during the last glacial period, consistent with the high alpine setting of the cave. Geologic evidence precludes deformation mechanisms other than tectonic. These new data are consistent with vectors of continuous global positioning system measurements as well as instrumental seismicity data, and collectively suggest that the SEMP is an active fault and that lateral extrusion of the Eastern Alps is ongoing.