Seismotectonic Setting Research Articles

The 2009 L’Aquila earthquake coseismic rupture: open issues and new insights from 3D finite element inversion of GPS, InSAR and strong motion data

<p>We present a Finite Element inverse analysis of the static deformation field for the M<sub>w</sub>= 6.3, 2009 L’Aquila earthquake, in order to infer the rupture slip distribution on the fault plane. An univocal solution for the rupture slip distribution has not been reached yet with negative impact for reliable hazard scenarios in a densely populated area. In this study, Finite Element computed Green’s functions were implemented in a linear joint inversion scheme of geodetic (GPS and InSAR) and seismological (strong motion) coseismic deformation data. In order to fully exploit the informative power of our dense dataset and to honor the complexities of the real Earth, we implemented an optimized source model, represented by a fault plane subdivided in variable size patches, embedded in a high-resolution realistic three-dimensional model of the Apenninic seismo-tectonic setting, accounting for topographic reliefs and rheological heterogeneities deduced from local tomography. We infer that the investigated inversion domain contains two minima configurations in the solution space, i.e. a single- and a double-patch slip distribution, which are almost equivalent, so that the available datasets and numerical models are not able to univocally discriminate between them. Nevertheless our findings suggest that a two high-slip patch pattern is slightly favoured.</p>

Spatial variations of earthquake occurrence and coseismic deformation in the Upper Rhine Graben, Central Europe

Seismic activity in the densely populated Upper Rhine Graben (URG) is an aspect in the public, political, and industrial decision making process. The spatial analysis of magnitude–frequency distributions provides valuable information about local seismicity patterns and regional seismic hazard assessment and can be used also as a proxy for coseismic deformation to explore the seismo-tectonic setting of the URG.We combine five instrumental and one historic earthquake bulletins to obtain for the first time a consistent database for events with local magnitudes ML≥2.0 in the whole URG and use it for the determination of magnitude frequencies. The data processing results in a dataset with 274 Poisson distributed instrumentally recorded earthquakes within the URG between 01/1971 and 02/2012 and 34 historic events since the year 1250.Our analysis reveals significant b-value variations along the URG that allow us to differentiate four distinct sections (I–IV) with significant differences in earthquake magnitude distributions: I: Basel region in the Swiss–France–German border region (b=0.83), II: region between Mulhouse and Freiburg in the southern URG (b=1.42), III: central URG (b=0.93), and IV: northern URG (b=1.06). High b-values and thus a relatively low amount of high magnitude events in the Freiburg section are possibly a consequence of strongly segmented, small-scale structures that are not able to accumulate high stresses.We use the obtained magnitude–frequency distributions and representative source mechanisms for each section to determine coseismic displacement rates. A maximum horizontal displacement rate of 41μm/a around Basel is found whereas only 8μm/a are derived for the central and northern URG. A comparison with geodetic and geological constraints implies that the coseismic displacement rates cover less than 10% of the overall displacement rates, suggesting a high amount of aseismic deformation in the URG.

Hydrodynamic, neotectonic and climatic control of the evolution of a barrier beach in the microtidal environment of the NE Ionian Sea (eastern Mediterranean)

The existence of barrier beaches is crucial, as they act as a buffer zone to the associated wetlands, whilst they are sensitive to climate change. The present study offers an insight into the processes controlling the formation and evolution of the Gyra barrier beach (NW coast of the island of Lefkada) in the microtidal, tectonically very active Ionian Sea under the influence of regional climate change and human interference. Such investigations are sparse in the literature. Existing information regarding regional geology, sediment availability and human intervention is combined with the collection of geophysical data, field observations and simulations of nearshore hydro- and sediment dynamics, analysis of climatic variations with respect to offshore wind/wave patterns (including storminess), in situ measurements of recent morphometric changes (2006–2008) and historical shoreline changes (since the 1960s). The recent formation and evolution (mostly under retreat) of the Gyra barrier beach is shown to be the combined result of the regional seismotectonic setting, relative increase of sea level, coastal sediment transport patterns, as well as human impact (negative) on primarily terrestrial sediment influxes. The current erosional trend of the barrier beach is associated with a shift in the wind and wave direction (from SW to NW) of extreme storm events in the Ionian Sea since the 1980s. The regional climatic variations of the last decades are well correlated with the trend of the North Atlantic Oscillation.

Mapping b-Value Anomalies Along the Indonesian Island Chain: Implications for Upcoming Earthquakes

In this study, the geospatial frequency–magnitude distribution (FMD) b-value images of the prospect sources of upcoming earthquakes were investigated along the Indonesian Sunda Margin (ISM) that strikes parallel to and near the Indonesian Island chain. After enhancing the completeness and stability of the earthquake catalogue, the seismicity data were separated according to their seismotectonic setting into shallow crustal and Intraslab earthquakes. In order to verify the spatial relationship between the b-values and the occurrence of subsequent major earthquakes, the complete shallow crustal seismicity dataset (1980–2005) was truncated into the 1980–2000 sub-dataset. Utilizing the suitable assumption of fixed-number of earthquakes, retrospective tests of both the complete and truncated datasets supported that areas of comparatively low b-values could reasonably be expected to predict likely hypocenters of future earthquakes. As a result, the present-day distributions of b-values derived from the complete (1980–2005) shallow crustal and Intraslab seismicity datasets revealed eight and six earthquake-prone areas, respectively, along the ISM. Since most of these high risk areas proposed here are quite close to the major cities of Indonesia, attention should be paid and mitigation plans should be developed for both seismic and tsunami hazards.

Probabilistic seismic hazard analysis at a strategic site in the Bay of Bengal

Probabilistic seismic hazard analysis (PSHA) along the route of an offshore pipeline for the transport of oil in the Bay of Bengal has been performed, in order to set up design parameters and identify possible geohazards. The complexity of geological and seismotectonic setting of the region where the pipeline is planned to be installed is the result of the interaction of the Indian, Eurasian and Burmese tectonic plates. In order to properly account for the intricate way by which these plates interact, a large area extending 450 km from the pipeline route has been considered for the compilation of a comprehensive earthquake catalogue, spanning the period 1663–2012 AD. Differently from earlier PSHA analyses conducted in the region based on assuming two-dimensional polygons as seismogenic provinces, this study adopted a seismotectonic source model which also includes for the first time a linear tectonic lineament representing the northward extension of the Sunda mega thrust, responsible for the large Sumatra–Andaman earthquake of 26 December 2004. Hazard computations have been performed over a grid of sites spaced 0.045° covering a rectangular area which contains the pipeline. Epistemic uncertainty in the hazard computations has been taken into account by a logic tree framework, incorporating different seismotectonic source models, maximum cut-off magnitude and ground-motion prediction equations. Horizontal median uniform hazard spectra and median uniform hazard spectra plus and minus one sigma on stiff ground have been calculated at the selected sites for different return periods. Peak ground acceleration with 10 % probability of exceedance in 50 years has been compared with values from previous hazard studies available for Bangladesh.

GIS-based landslide susceptibility zonation using bivariate statistical and expert approaches in the city of Constantine (Northeast Algeria)

The city of Constantine has suffered frequent landslides during the last few decades because of its geological, geomorphological, climatic and seismotectonic setting as well as anthropic activities. In this work we perform a landslide susceptibility zonation (LSZ) zonation by using bivariate statistical and expert approaches in GIS technology for this area. Firstly, a landslide inventory map was constructed from interpretation of aerial photographs, high resolution satellite images, field surveys and bibliographies. Then various causal factors such as lithology, slope, aspect, precipitation, land use, distance to streams, distance to faults and anthropogenic factors like distance to roads associated with landslide activity were considered and the corresponding thematic layers generated using GIS techniques. The relative importance of these layers in causing landslides has been evaluated using bivariate statistics and expert methods to generate LSZ maps. The expert-based method provided a subjective classification of the study area in terms of landslide susceptibility which does not completely fit the landslide field survey. However unlikely, the bivariate statistics-based method provided the most satisfying results and appears to be the most accurate. Indeed, results show that 27.2 % of the study area lies within a very high to high susceptibility zone that encompasses 73.64 % of the existing landslides. Moderate, low and very low susceptibility zones cover, respectively, 25.7, 21.7 and 25.4 % of the study area. The LSZ maps generated may serve as useful tools for land management and planning in the Constantine region.

Historical and pre-historical tsunamis in the Mediterranean and its connected seas: Geological signatures, generation mechanisms and coastal impacts

Abstract The origin of tsunamis in the Mediterranean region and its connected seas, including the Marmara Sea, the Black Sea and the SW Iberian Margin in the NE Atlantic Ocean, is reviewed within the geological and seismotectonic settings of the region. A variety of historical documentary sources combined with evidence from onshore and offshore geological signatures, geomorphological imprints, observations from selected coastal archeological sites, as well as instrumental records, eyewitnesses accounts and pictorial material, clearly indicate that tsunami sources both seismic and non-seismic (e.g. volcanism, landslides) can be found in all the seas of the region with a variable tsunamigenic potential. Local, regional and basin-wide tsunamis have been documented. An improved map of 22 main tsunamigenic zones and their relative potential for tsunami generation is presented. From west to east, the most important tsunamigenic zones are situated offshore SW Iberia, in the North Algerian margin, in the Tyrrhenian Calabria and Messina Straits, in the western and eastern segments of the Hellenic Arc, in the Corinth Gulf of Central Greece, in the Levantine Sea offshore the Dead Sea Transform Fault and in the eastern side of the Marmara Sea. Important historical examples, including destructive tsunamis associated with large earthquakes, are presented. The mean recurrence of strong tsunamis in the several basins varies greatly but the highest event frequency (1/96 years) is observed in the east Mediterranean basin. For most of the historical events it is still unclear which was the causative seismic source and if the tsunami was caused by co-seismic slip, by earthquake-triggered submarine landslides or by a combination of both mechanisms. In pre-historical times, submarine volcanic eruptions (i.e. caldera collapse, massive pyroclastic flows, volcanogenic landslides) and large submarine landslides caused important tsunamis although little is known about their source mechanisms. We conclude that further investigation of the tsunami generation mechanisms is of primary importance in the Mediterranean region. Inputs from tsunami numerical modeling as well as from empirical discrimination criteria for characterizing tsunami sources have been proved particularly effective for recent, well-documented, aseismic landslide tsunamis (e.g., 1963 Corinth Gulf, 1979 Cote d'Azur, 1999 Izmit Bay, 2002 Stromboli volcano). Since the tsunami generation mechanisms are controlled by a variety of factors, and given that the knowledge of past tsunami activity is the cornerstone for undertaking tsunami risk mitigation action, future interdisciplinary research efforts on past tsunamis are needed.

Ground Motion Relations for Active Regions in India

In this article, a study on development of ground motion prediction equations (GMPEs) is undertaken for seismically active regions in India. To derive the equations, the seismically active regions are divided into four units based on seismotectonic setting and geology. Due to lack of strong motion data, a stochastic finite-fault simulation method is used for generating a complete synthetic database with respect to magnitude and distance. The input parameters in the stochastic seismological model, such as site amplification and stress drop, are first derived from the past strong-motion data. A total of 236 three-component records from 62 earthquakes with magnitudes ranging from M w 3.4 to 7.8 are used to calibrate the seismological model. The obtained stress drops of these 62 events lie in between 60 and 165 bars. With the help of a large synthetic database generated from the calibrated seismological model, ground motion relations for 5 % damped spectral acceleration are obtained by regression analysis. The developed ground motion relations are compared with the existing GMPEs of the other active regions in the world. Although the proposed equations have trends similar to those of the existing relations, there are some differences attributed to stress drop and the quality factor of active regions in India. These relations will be useful to prepare spectral acceleration hazard maps of India for a given annual probability of exceedance.

The 2013 Marche offshore earthquakes: new insights into the active tectonic setting of the outer northern Apennines

A seismic sequence offshore the Marche region sheds new light on the active tectonic setting of the outer northern Apennines, revealing the existence of a previously unknown transcurrent seismogenic structure. In contrast to the Po Plain area, where vigorous seismicity testifies to active frontal thrusting, the seismotectonic setting of the Adriatic domain is characterized by the occurrence of active crustal strike-slip faults dissecting the thrust belt. As recent studies suggest that thrust faults represent the unique seismogenic sources characterizing the Adriatic sector of the outer northern Apennines, our results pose new challenges to the identification of seismogenic structures in the region.

Possible Triggered Seismicity Signatures Associated with the Vrancea Intermediate-Depth Strong Earthquakes (Southeast Carpathians, Romania)

Online Material: Vrancea earthquake catalogs. To date, no generally applicable procedure is available for distinguishing triggered earthquakes from other seismic events that occur, apparently randomly, within a certain region (see discussion in van der Elst and Brodsky, 2010). In particular, it is not habitual to utilize diagrams illustrating the time evolution of the seismic release (e.g., Mantovani et al. , 1987; Husen et al. , 2004) as a diagnostic tool. However, that investigation method has been shown in the present study to be outstandingly useful for highlighting similarities existing between the patterns of seismic activities recorded in two distinct and possibly interacting lithospheric domains associated with the Carpathians orogenic belt in Romania. The main potentially causative earthquakes occurred in the Vrancea seismic zone (hereafter VSZ), located at intermediate depths (60–180 km) beneath the southeast Carpathian Arc bend (Fig. 1), whereas the resulting seismicity enhancements (recorded several months to tens of months afterward) developed at less than 60 km depth in the adjoining Carpathians‐foredeep region. The concerned Carpathians Mountains foreland basement is built up of two distinct lithospheric plates: the east European plate to the north‐northeast and the Moesian plate to the south‐southwest (Fig. 1), which are separated by a regional system of northwest–southeast‐oriented fractures (the so‐called Trotus and Peceneaga‐Camena faults). In coincidence with that contact, a shallow seismicity domain, designated (Raileanu et al. , 2007) as the Marasesti–Galaţi–Braila lineament (hereafter MGBL), has also been delineated. Figure 1. General seismotectonic setting of the considered area (geology after Sandulescu, 1984). The Carpathian Mountains accretionary wedge has overthrust (saw‐tooth boundary) the corresponding foreland, which extended on two major plates (east European and Moesian). The roughly oval, solid contour bounds the epicentral domain of the intermediate‐depth (≥60 km) Vrancea earthquakes. Large black symbols …

The April 2012 Indian Ocean earthquakes: Seismotectonic context and implications for their mechanisms

The 11 April 2012 earthquakes (M-w 8.6 and M-w 8.2) were sourced within the Northern Wharton Basin in the northeastern part of the Indo-Australian diffuse plate boundary. This unusually active oceanic intraplate region has generated many large earthquakes in the past, most of which are believed to have occurred by strike-slip motion, triggered by the NW-SE oriented compressional stresses acting across the Indian and Australian plates. In the aftermath of the 2004 megathrust earthquake along the nearby Sunda Trench, increased seismicity in the Northern Wharton Basin is attributed to the stress transfer from the Sumatra-Andaman plate boundary. Models proposed for the April 2012 earthquakes differ somewhat in details but partly attribute their complex rupture to the reactivation of pre-existing structures. These structures include previously mapped N-S trending fracture zones within the Northern Wharton Basin and E-W lineations across the Ninetyeast Ridge. In this paper, we review the regional tectonics and past seismicity on the Indo-Australian Plate in order to understand the seismotectonic setting of the April 2012 Indian Ocean earthquakes. (c) 2014 Elsevier B.V. All rights reserved.

Aftershock relocation and frequency–size distribution, stress inversion and seismotectonic setting of the 7 August 2013 M=5.4 earthquake in Kallidromon Mountain, central Greece

Abstract On August 7, 2013 a moderate earthquake (NOA ML = 5.1, NOA Mw = 5.4) occurred in central Kallidromon Mountain, in the Pthiotis region of central Greece. 2270 aftershocks were relocated using a modified 1-D velocity model for this area. The b-value of the aftershock sequence was b = 0.85 for a completeness magnitude of Mc = 1.7. The rate of aftershock decay was determined at p = 0.63. The spatial distribution of the aftershock sequence points towards the reactivation of a N70° ± 10°E striking normal fault at crustal depths between 8 and 13 km. A NNW–SSE cross-section imaged the activation of a steep, south dipping normal fault. A stress inversion analysis of 12 focal mechanisms showed that the minimum horizontal stress is extensional at N173°E. No primary surface ruptures were observed in the field; however, the earthquake caused severe damage in the villages of the Kallidromon area. The imaged fault strike and the orientation of the long-axis of the aftershock sequence distribution are both at a high-angle to the strike of known active faults in this area of central Greece. We interpret the Kallidromon seismic sequence as release of extensional seismic strain on secondary, steep faults inside the Fokida–Viotia crustal block.

First Determination of Source Parameters of Moderate Earthquakes (4.1 ≤ M ≤ 5.1) in Morocco from Spectral Analysis

Recent installation of an array of broad band seismological stations in Morocco allowed us to study the records of five recent (2005-2008) moderate earthquakes (4.1 ≤ M ≤ 5.1) in order to determine their source parameters (seismic moment, fault slip, rupture area and stress drop) from P-wave spectra. We also studied the older Rissani events of 1992 using teleseismic data. Values of Mo, r, Δu and Δσ are, respectively, 1.1 × 1013 - 6 × 1016 Nm; 0.50 - 3.9 km; 0.8 - 5.8 cm and 0.3 - 1.49 MPa. The results are in accordance with the seismotectonic and geodynamic setting of Morocco as, for instance, the amount of slip along the faults with respect to the relative displacement of Nubia to Iberia (~4 mm·yr-1) determined from GPS data, taking into account the period of stress accumulation. However, some events show very variable corner frequency and low-frequency amplitude values which lead to considerably higher stress drop and fault slip values, especially at the nearest stations, which may reflect some site effects or uncertainties on depth and take-off angles.

Analysis of precursory seismicity patterns in Zagros (Iran) by CN algorithm

This study illustrates the application of the CN algorithm for the analysis of precursory seismicity patterns in the Zagros region (Iran), an area characterized by a complex seismotectonic setting and by remarkable seismic activity. CN is a formally defined and widely tested algorithm for intermediate-term middle-range earthquake prediction, based on the analysis of routinely compiled earthquake catalogs. To allow its application, the global and regional catalogs available for the territory of Iran have been analyzed so as to compile a data set sufficiently complete and homogeneous over a time span of about 3 decades, as required for CN application. A number of tests have been performed with respect to changes in the input catalogs, assuming different magnitude completeness levels as well as considering different magnitude thresholds for the selection of target earthquakes. Different variants of the regionalization have been outlined according to the seismotectonic model, and it was concluded that precursory seismicity patterns for the largest events need to be researched in the whole Zagros tectonic domain. Accordingly, an experiment was set up aimed at validation of intermediate-term middle-range prediction of earthquakes with magnitude M >= 6.0 in the Zagros region. Starting in March 2012, CN prediction results have been routinely updated based on the events with M >= Mc = 4.0 as they are reported in the International Seismological Centre catalog.

Tectonic setting of the recent damaging seismic series in the Southeastern Betic Cordillera, Spain

In this work we analyze the tectonic setting of the recent damaging seismic series occurred in the Internal Zones of the eastern Betic Cordillera (SE Spain) and surrounding areas, the tectonic region where took place the 11th May 2011 Mw 5.2 Lorca earthquake. We revisit and make a synthesis of the seven largest and damaging seismic series occurred from 1984 to 2011. We analyze their seismotectonic setting, and their geological sources under the light of recent advances in the knowledge on active faults, neotectonics, seismotectonics and stress regime, with special attention focused on the Lorca Earthquake. These seismic series are characterized by two types of focal mechanisms, produced mainly by two sets of active faults, NNW–SSE to NNE–SSW small (no larger than 20–30 km) extensional faults with some strike slip component, and E–W to NE–SW large strike slip faults (more than 50 km long) with some compressional component (oblique slip faults). The normal fault earthquakes related to the smaller faults are dominant in the interior of large crustal tectonic blocks that are bounded by the large E–W to NE–SW strike-slip faults. The strike slip earthquakes are associated to the reactivation of segments or intersegment regions of the large E–W to NE–SW faults bounding those crustal tectonic blocks. Most of the seismic series studied in this work can be interpreted as part of the background seismicity that occurs within the crustal blocks that are strained under a transpressional regime driven by the major strike slip shear corridors bounding the blocks. The seismotectonic analysis and the phenomenology of the studied series indicate that it is usual the occurrence of damaging compound earthquakes of M $$\sim $$ 5.0 associated with triggering processes driven by coseismic stress transfer. These processes mainly occur in the seismic series generated by NNW–SSE to NNE–SSW faults. These mechanical interaction processes may induce a higher frequency of occurrence of this kind of earthquakes than considered in traditional probabilistic seismic hazard assessments and it should be taken into account in future seismic hazard assessments.

Effects of multiple earthquakes on inelastic structural response

The basic approach for seismic design of structures utilizes a single loading scenario and a single performance criterion; usually life-safety. In recent years, social and economic considerations have necessitated that more than one performance criterion is used, and also more than one level of earthquake intensity. This multiple load-and-limit state seismic design is the current best practice. There are a few locations around the world that warrant an alternative approach. These locations are affected by more than one earthquake within a relatively short period of time due to their special seismo-tectonic setting. Few existing studies simply assume that the first earthquake will impose the maximum damage. An opportunity has presented itself to study the effect of multiple strong earthquakes on structures as a consequence to the exceptionally rich set of records obtained from the earthquake sequence of Tohoku (Japan), starting on March 2011. In this technical note, five stations are selected to represent a set of sites subjected to multiple earthquakes of varying magnitudes and source-to-site distances. From the tens of records captured at these five sites, three are selected for each site to represent scenarios of leading and trailing strong-ground motion. A leading set is where the first earthquake has the largest peak ground acceleration (PGA) in the sequence of three, while a trailing set has the second or third records as its highest PGA signal. A short list of earthquake response parameters is selected, and the records are treated in two different manners. Inelastic constant ductility spectra for acceleration response are examined, alongside force reduction factor spectra. The final part of the technical note is a reinforced concrete (RC) frame analysis subjected to the same set of ground motions used for the response spectra. The inelastic response and force reduction factor spectra, alongside the inelastic response of the RC frame, not only confirm that multiple earthquakes deserve extensive and urgent studies, but also give indications of the levels of lack of conservatism in the safety of conventionally-designed structures when subjected to multiple earthquakes.

Assessing performances of pattern informatics method: a retrospective analysis for Iran and Italy

Pattern informatics (PI) algorithm, which was introduced at the beginning of past decade, uses instrumental earthquake catalogs to investigate the time-dependent rate of seismicity in the study area and, based on the information from past events, calculates the probabilities for the occurrence of future large earthquakes. The main measure in this method is the number of events above a specified magnitude threshold M c that is counted over a gridded area. PI has been applied in several regions of the world and different variants of the method have been developed over the past decade. Hence, the problem of formally evaluating and comparing the performances of the different PI variants needs to be addressed from an operational perspective, in order to identify the preferred application scheme and as well as to improve the performances of the method. In this study, PI is applied for the first time to the retrospective analysis of the earthquake catalogs of Iran and Italy, so as to check whether this method could forecast the past large events in these two regions with different level of data completeness and complex seismotectonic setting. The original PI algorithm and one of its modified variants, as well as the relative intensity (RI) model, are used to check the stability and statistical significance of the obtained results. In order to assess and compare the obtained results, the performances of the different PI variants are analyzed considering different evaluation strategies, which turn out to provide significantly different scores even for the same algorithm variant. We show that a critical point in the assessment of the obtained results is related with the definition and quantification of the space uncertainty of the issued forecasts, that is, with the extent of the territory where large earthquakes are to be expected. Accordingly, we emphasize the need for an appropriate definition of the evaluation strategies, clearly and unambiguously indicating the area where a large earthquake has to be expected. The study shows that, with respect to application in Iran and Italy, the performances of PI algorithm (both original and modified variants) are highly dependent on the selected evaluation strategy and do not provide better information than the simple RI model, which does not account for temporal properties of seismicity evolution. The overall performances can be improved by introducing specific thresholds that discard the less active cells; however, being based on some posterior optimization, a rigorous prospective testing is required to assess the forecasting capability of the method. In this paper, we aim to set up the rules for such testing, including advance definition of the evaluation strategy.

An overview of the consequences of paraglacial landsliding on deglaciated mountain slopes: typology, timing and contribution to cascading fluxes

Three decades after the early definition of the concept, a general model of paraglaciation was established, integrating the typical sediment paraglacial cascading system and the responses of associated sediment storages. The residuals of this model should now be examined and explained through controlling factors that may act at both regional (e.g. tectonics) and local (topography, lithology, etc.) scales. We compare here the patterns identified in a few mountain ranges of the northern hemisphere, located in various seismotectonic settings (especially western Alps, northwestern Scotland, central Norway, Svalbard and Iceland). By combining our field observations with a literature review, the effectiveness of the paraglacial response on mountain-slope erosion and the contribution of paraglaciation to the sedimentary cascading system are discussed. In most cases, paraglaciation generates sediment storage and aggradation in headwaters and glacial trough, as the evacuation rate into sinks remains low. Finally, paraglaciation appears to be a period of hillslope denudation, preparing reservoirs of sediments, which can only be effectively evacuated during further glaciation periods.

The tectonic puzzle of the Messina area (Southern Italy): Insights from new seismic reflection data

The Messina Strait, that separates peninsular Italy from Sicily, is one of the most seismically active areas of the Mediterranean. The structure and seismotectonic setting of the region are poorly understood, although the area is highly populated and important infrastructures are planned there. New seismic reflection data have identified a number of faults, as well as a crustal scale NE-trending anticline few km north of the strait. These features are interpreted as due to active right-lateral transpression along the north-eastern Sicilian offshore, coexisting with extensional and right-lateral transtensional tectonics in the southern Messina Strait. This complex tectonic network appears to be controlled by independent and overlapping tectonic settings, due to the presence of a diffuse transfer zone between the SE-ward retreating Calabria subduction zone relative to slab advance in the western Sicilian side.

The East Anatolian Fault Zone: Seismotectonic setting and spatiotemporal characteristics of seismicity based on precise earthquake locations

The East Anatolian Fault Zone (EAFZ) represents a plate boundary extending over ∼500 km between the Arabian and Anatolian plates. Relative plate motion occurs with slip rates ranging from 6 to 10 mm/yr and has resulted in destructive earthquakes in eastern Turkey as documented by historical records. In this study, we investigate the seismic activity along the EAFZ and fault kinematics based on recordings from a densified regional seismic network providing the best possible azimuthal coverage for the target region. We optimize a reference 1‐D velocity model using a grid‐search approach and re‐locate hypocenters using the Double‐Difference earthquake relocation technique. The refined hypocenter catalog provides insights into the kinematics and internal deformation of the fault zone down to a resolution ranging typically between 100 and 200 m. The distribution of hypocenters suggests that the EAFZ is characterized by NE‐SW and E‐W oriented sub‐segments that are sub‐parallel to the overall trend of the fault zone. Faulting mechanisms are predominantly left‐lateral strike‐slip and thus in good correlation with the deformation pattern derived from regional GPS data. However, we also observe local clusters of thrust and normal faulting events, respectively. While normal faulting events typically occur on NS‐trending subsidiary faults, thrust faulting is restricted to EW‐trending structures. This observation is in good accordance with kinematic models proposed for evolving shear zones. The observed spatiotemporal evolution of hypocenters indicates a systematic migration of micro‐ and moderate‐sized earthquakes from the main fault into adjacent fault segments within several days documenting progressive interaction between the major branch of the EAFZ and its secondary structures. Analyzing the pre versus post‐seismic phase for M > 5 events we find that aftershock activities are initially spread to the entire source region for several months but start to cluster at the central part of the main shock rupture thereafter.