scholarly journals Recent Seismicity in the Area of the Major, 1908 Messina Straits Earthquake, South Italy

2021 ◽  
Vol 9 ◽  
Author(s):  
Giancarlo Neri ◽  
Barbara Orecchio ◽  
Debora Presti ◽  
Silvia Scolaro ◽  
Cristina Totaro
Keyword(s):  
Focal Mechanisms ◽  
Current Debate ◽  
Tyrrhenian Sea ◽  
Primary Role ◽  
Normal Faulting ◽  
Study Region ◽  
Northern Border ◽  
Fractured Medium ◽  
Horizontal Strain ◽  
Subducting Slab

High-quality non-linear hypocenter locations and waveform inversion focal mechanisms of recent, shallow earthquakes of the Messina Straits have allowed us to obtain the following main results: 1) seismicity has occurred below the east-dipping north-striking fault proposed by most investigators as the source of the 1908, magnitude 7.1 Messina earthquake, while it has been substantially absent in correspondence of the fault and above it; 2) earthquake locations and related strain space distributions do not exhibit well defined trends reflecting specific faults but they mark the existence of seismogenic rock volumes below the 1908 fault representing primary weakness zones of a quite fractured medium; 3) focal mechanisms reveal normal and right-lateral faulting in the Straits, reverse faulting at the southern border of it (Ionian sea south of the Ionian fault), and normal faulting at the northern border (southeastern Tyrrhenian sea offshore southern Calabria); 4) these faulting regimes are compatible with the transitional character of the Messina Straits between the zone of rollback of the in-depth continuous Ionian subducting slab (southern Calabria) and the collisional zone where the subduction slab did already undergo detachment (southwest of the Ionian fault); 5) the whole seismicity of the study area, including also the less recent earthquakes analyzed by previous workers, is compared to patterns of geodetic horizontal strain and uplift rates available from the literature. We believe that the joint action of Africa-Europe plate convergence and rollback of the Ionian subducting slab plays a primary role as regard to the local dynamics and seismicity of the Messina Straits area. At the same time, low horizontal strain rates and large spatial variations of uplift rate observed in this area of strong normal-faulting earthquakes lead us to include a new preliminary hypothesis of deep-seated sources concurring to local vertical dynamics into the current debate on the geodynamics of the study region.

scholarly journals Regional centroid MT inversion of small to moderate earthquakes in the Alps using the dense AlpArray seismic network: challenges and seismotectonic insights

2021 ◽  
Author(s):  
Gesa Maria Petersen ◽  
Simone Cesca ◽  
Sebastian Heimann ◽  
Peter Niemz ◽  
Torsten Dahm ◽  
...  
Keyword(s):  
Seismic Activity ◽  
Clustering Algorithm ◽  
Moment Tensor ◽  
Focal Mechanisms ◽  
Seismic Network ◽  
Central Alps ◽  
Normal Faulting ◽  
Data Types ◽  
Study Region ◽  
Northern Dinarides

Abstract. The Alpine mountains in central Europe are characterized by a heterogeneous crust accumulating different tectonic units and blocks in close proximity to sedimentary foreland basins. Centroid moment tensor inversion provides insight into the faulting mechanisms of earthquakes and related tectonic processes, but is significantly aggravated in such an environment. Thanks to the dense AlpArray seismic network and our flexible bootstrap-based inversion tool Grond we are able to test different set-ups with respect to the uncertainties of the obtained moment tensors and centroid locations. We evaluate the influence of frequency bands, azimuthal gaps, input data types and distance ranges and study the occurrence and reliability of non-DC components. We infer that for most earthquakes (Mw ≥ 3.3) a combination of time domain full waveforms and frequency domain amplitude spectra in a frequency band of 0.02–0.07 Hz is suitable. Relying on the results of our methodological tests, we perform deviatoric MT inversions for events with Mw > 3.0. We present here 75 solutions and analyse our results in the seismo-tectonic context of historic earthquakes, seismic activity of the last three decades and GNSS deformation data. We study regions of high seismic activity, namely the western Alps, the region around Lake Garda, the SE Alps, besides clusters further from the study region, in the northern Dinarides and the Apennines. Seismicity is particularly low in the eastern Alps and in parts of the central Alps. We apply a clustering algorithm to focal mechanisms, considering additional focal mechanisms from existing catalogs. Related to the NS compressional regime, E-W to ENE-WSW striking thrust faulting is mainly observed in the Friuli area in the SE Alps. Strike-slip faulting with a similarly oriented pressure axis is observed along the northern margin of the central Alps and in the northern Dinarides. NW-SE striking normal faulting is observed in the NW Alps showing a similar strike direction as normal faulting earthquakes in the Apennines. Both, our centroid depths as well as hypocentral depths in existing catalogs indicate that Alpine seismicity is predominantly very shallow; about 80 % of the studied events have depths shallower than 10 km.

Seismic doublets and a complex seismic sequence controlled by the rotation of the Juan Fernández microplate

2021 ◽  
Author(s):  
Simone Cesca ◽  
Carla Valenzuela Malebrán ◽  
José Ángel López-Comino ◽  
Timothy Davis ◽  
Carlos Tassara ◽  
...  
Keyword(s):  
Source Parameters ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Joint Analysis ◽  
Seismic Sequence ◽  
Local Data ◽  
Study Region ◽  
Coulomb Stress Changes ◽  
Earthquake Source Parameters ◽  
Stress Changes

<p> A complex seismic sequence took place in 2014 at the Juan Fernández microplate, a small microplate located between Pacific, Nazca and Antarctica plates. Despite the remoteness of the study region and the lack of local data, we were able to resolve earthquake source parameters and to reconstruct the complex seismic sequence, by using modern waveform-based seismological techniques. The sequence started with an exceptional Mw 7.1-6.7 thrust – strike slip earthquake doublet, the first subevent being the largest earthquake ever recorded in the region and one of the few rare thrust earthquakes in a region otherwise characterized by normal faulting and strike slip earthquakes. The joint analysis of seismicity and focal mechanisms suggest the activation of E-W and NE-SW faults or of an internal curved pseudofault, which is formed in response to the microplate rotation, with alternation of thrust and strike-slip earthquakes. Seismicity migrated Northward in its final phase, towards the microplate edge, where a second doublet with uneven focal mechanisms occurred. The sequence rupture kinematics is well explained by Coulomb stress changes imparted by the first subevent. Our analysis show that compressional stresses, which have been mapped at the northern boundary of the microplate, but never accompanied by large thrust earthquakes, can be accommodated by the rare occurrence of large, impulsive, shallow thrust earthquakes, with a considerable tsunamigenic potential.</p>

Strike-Slip Earthquakes at the Northern Edge of the Calabrian Arc Subduction Zone

2020 ◽  
Author(s):  
Giovanna Calderoni ◽  
Anna Gervasi ◽  
Mario La Rocca ◽  
Guido Ventura
Keyword(s):  
Subduction Zone ◽  
Shear Zones ◽  
Strike Slip ◽  
Corner Frequency ◽  
Tyrrhenian Sea ◽  
Northern Border ◽  
Source Directivity ◽  
Northern Edge ◽  
East West ◽  
Good Agreement

Abstract We analyzed earthquakes of a swarm started in October 2019 in the Tyrrhenian Sea, at the northern border of the Calabrian arc subduction zone. The swarm is located in the same area where a subduction-transform edge propagator (STEP) shear- zone -oriented east–west is recognized from ocean floor morphology and submarine volcanoes. We computed focal mechanism, relative location, stress drop, corner frequency, and source directivity of the mainshock Mw 4.4 and of some aftershocks in the local magnitude range 2.3–3.7. Results indicate clearly that the mainshock occurred on a northwest–southeast-oriented fault, with right-lateral strike-slip motion, and it was characterized by a strong directivity of the rupture propagation from northwest to southeast. On the contrary, most of aftershocks were located on another strike-slip fault oriented northeast–southwest and had left-lateral kinematics. The kinematic features of these earthquakes indicate a strain field with the P-axis oriented north–south and the T-axis oriented east–west. Fault directions and stress field are in good agreement with the theoretical fracture model of shear zones associated with a STEP.

scholarly journals Distributed earthquake focal mechanisms in the Aegean Sea

2018 ◽  
Vol 40 (3) ◽  
pp. 1125 ◽  
Author(s):  
A. Kiratzi ◽  
C. Benetatos ◽  
Z. Roumelioti
Keyword(s):  
Aegean Sea ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Normal Faulting ◽  
Small Magnitude ◽  
The North ◽  
Earthquake Focal Mechanisms ◽  
Reverse Faulting ◽  
Different Types ◽  
Transform Fault Zone

Nearly 2,000 earthquake focal mechanisms in the Aegean Sea and the surroundings for the period 1912- 2006, for 1.5 <M<7.5, and depths from 0 to 170 km, indicate a uniform distribution and smooth variation in orientation over wide regions, even for the very small magnitude earthquakes. ~ 60% of the focal mechanisms show normal faulting, that mainly strikes ~E-W. However, a zone ofN-S normal faulting runs the backbone of Albanides-Hellenides. Low-angle thrust and reverse faulting is confined in western Greece (Adria-Eurasia convergence) and along the Hellenic trench (Africa-Eurasia). In the central Aegean Sea the effect of the propagating tip of the North Anatolian Fault into the Aegean Sea is pronounced and strike-slip motions are widely distributed. Shearing does not cross central Greece. Strike-slip motions reappear in the Cephalonia-Lefkada Transform Fault zone and in western Péloponnèse, which shows very complex tectonics, with different types of faulting being oriented favourably and operating under the present stress-field. Moreover, in western Péloponnèse the sense of the observed shearing is not yet clear, whether it is dextral or sinistral, and this lack of data has significant implications for the orientation of the earthquake slip vectors compared to the GPS obtained velocity vectors.

scholarly journals Parageneses of fractures in large fault zones of West Transbaikalia

2018 ◽  
Vol 9 (3) ◽  
pp. 889-908
Author(s):  
A. V. Cheremnykh
Keyword(s):  
Quantitative Analysis ◽  
Fault Zones ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Rock Fracturing ◽  
Study Region ◽  
Tectonic Development ◽  
Paleoseismic Dislocations ◽  
The Right ◽  
Cenozoic Sediments

Our study was focused on the parageneses of heterogeneous fractures in the large fault zones of West Transbaikalia,Russia. We reconstructed the latest deformation in the fault zones of Transbaikalia, within which paleoseismic dislocations are known and M 4.7 earthquakes take place. To obtain statistically justified solutions on the kinematic types of the largest faults ofWest Transbaikalia, we collected the required data and conducted the structural and paragenetic analysis of the fractures in the study area. In the Chikoi-Ingoda, Khilok, North Tugnui andNorth Zaganfault zones, we created a network of 54 observation points and measured more than 5500 details of local fractures and faults. Recorded were the observed slickensides, the displacements of markers, and other details of rock fracturing. Based on the analysis results, we calculated a ratio of heterochronous dynamic settings for formation of the observed fault group. It shows that NW-SE-trending extension and compression are dominant in the study region. The parageneses of E-NE-striking faults, i.e. regional faults longitudinal to the depressions ofWest Transbaikalia, are abundant in the studied fault zones and generally observed in heterochronous formations, including the Cenozoic sediments. This fact, along with the focal mechanisms of the recently recorded earthquakes, suggests that these faults are young. Besides, in the Tugnui basin and the area southeast of the Chikoy depression, the right-lateral strike-slip setting was reconstructed for E-NE-trending faults. Our study pioneers in the quantitative analysis of the fault parageneses ofWest Transbaikalia. Considering the development of the network of large faults in the study area, we reconstructed the main stages and the kinematic types of the second-order fractures that constitute the internal structure of the studied fault zones at each stage of their tectonic development. 

scholarly journals RECENT SEISMIC ACTIVITY IN CENTRAL GREECE REVEALING LOCAL SEISMOTECTONIC PROPERTIES

2017 ◽  
Vol 43 (4) ◽  
pp. 2075
Author(s):  
Ch. K. Karamanos ◽  
V. G. Karakostas ◽  
L. Seeber ◽  
E. E. Papadimitriou ◽  
A.A. Kilias
Keyword(s):  
Fault Zone ◽  
Fault Plane ◽  
Focal Mechanisms ◽  
Normal Faulting ◽  
Seismic Excitations ◽  
Lateral Component ◽  
Fault Plane Solutions ◽  
Central Greece ◽  
Source Characteristics ◽  
The Town

The December 2008, M=5.2 earthquake occurred in the Voiotikos–Kifissos basin near the town of Amfikleia in Central Greece and was followed by an intense sequence with hundreds of earthquakes. Mainshock source characteristics derived from the recordings of the Greek National Seismological Network are consistent with previous known earthquakes as well as with the current nearly N–S extensional regime. The adequate azimuthal coverage and the calculated time residuals at each seismological station ensure high location accuracy, whereas the stations operated close to the seismic excitations constrained 80% of the focal depths between 8 and 12km. Distances from the mainshock epicenter to the 10 closest seismological stations vary from 15 to 75 km. Hypoinverse and HypoDD were used for locations, and FPFIT was used for fault plane solutions of events with an adequate number of clear first arrivals. The hypocenters and focal mechanisms illuminate a ≈10km–long fault zone striking nearly E–W with oblique normal faulting and a small left lateral component. The Voiotikos–Kifissos basin is bordered in the south by two left–stepping en echelon segments known as the Pavliani fault zone and the Parnassos detachment, which strike NW and dip NE. In our preferred interpretation, the Amfikleia mainshock ruptured a previously recognized south–dipping fault antithetic to the basin border faults. This fault may be associated with the left step on the border fault, which would be releasing if that fault had a sinistral component.

scholarly journals Regional centroid moment tensor inversion of small to moderate earthquakes in the Alps using the dense AlpArray seismic network: challenges and seismotectonic insights

Solid Earth ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 1233-1257
Author(s):  
Gesa Maria Petersen ◽  
Simone Cesca ◽  
Sebastian Heimann ◽  
Peter Niemz ◽  
Torsten Dahm ◽  
...  
Keyword(s):  
Seismic Activity ◽  
Moment Tensor ◽  
Southern Alps ◽  
Moment Tensor Inversion ◽  
Seismic Network ◽  
Central Alps ◽  
Normal Faulting ◽  
Centroid Moment Tensor ◽  
Study Region ◽  
Northern Dinarides

Abstract. The Alpine mountains in central Europe are characterized by a heterogeneous crust accumulating different tectonic units and blocks in close proximity to sedimentary foreland basins. Centroid moment tensor inversion provides insight into the faulting mechanisms of earthquakes and related tectonic processes but is significantly aggravated in such an environment. Thanks to the dense AlpArray seismic network and our flexible bootstrap-based inversion tool Grond, we are able to test different setups with respect to the uncertainties of the obtained moment tensors and centroid locations. We evaluate the influence of frequency bands, azimuthal gaps, input data types, and distance ranges and study the occurrence and reliability of non-double-couple (DC) components. We infer that for most earthquakes (Mw≥3.3) a combination of time domain full waveforms and frequency domain amplitude spectra in a frequency band of 0.02–0.07 Hz is suitable. Relying on the results of our methodological tests, we perform deviatoric moment tensor (MT) inversions for events with Mw>3.0. Here, we present 75 solutions for earthquakes between January 2016 and December 2019 and analyze our results in the seismotectonic context of historical earthquakes, seismic activity of the last 3 decades, and GNSS deformation data. We study regions of comparably high seismic activity during the last decades, namely the Western Alps, the region around Lake Garda, and the eastern Southern Alps, as well as clusters further from the study region, i.e., in the northern Dinarides and the Apennines. Seismicity is particularly low in the Eastern Alps and in parts of the Central Alps. We apply a clustering algorithm to focal mechanisms, considering additional mechanisms from existing catalogs. Related to the N–S compressional regime, E–W-to-ENE–WSW-striking thrust faulting is mainly observed in the Friuli area in the eastern Southern Alps. Strike-slip faulting with a similarly oriented pressure axis is observed along the northern margin of the Central Alps and in the northern Dinarides. NW–SE-striking normal faulting is observed in the NW Alps, showing a similar strike direction to normal faulting earthquakes in the Apennines. Both our centroid depths and hypocentral depths in existing catalogs indicate that Alpine seismicity is predominantly very shallow; about 80 % of the studied events have depths shallower than 10 km.

The SWATH-D Seismological Network in the Eastern Alps

2021 ◽  
Vol 92 (3) ◽  
pp. 1592-1609 ◽  
Author(s):  
Benjamin Heit ◽  
Luigia Cristiano ◽  
Christian Haberland ◽  
Frederik Tilmann ◽  
Damiano Pesaresi ◽  
...  
Keyword(s):  
Eastern Alps ◽  
Focal Mechanisms ◽  
Seismic Network ◽  
Moho Depth ◽  
Dense Network ◽  
Study Region ◽  
The North ◽  
Complex Part ◽  
Broadband Network ◽  
The Alps

Abstract The SWATH-D experiment involved the deployment of a dense temporary broadband seismic network in the Eastern Alps. Its primary purpose was enhanced seismic imaging of the crust and crust–mantle transition, as well as improved constraints on local event locations and focal mechanisms in a complex part of the Alpine orogen. The study region is a key area of the Alps, where European crust in the north is juxtaposed and partially interwoven with Adriatic crust in the south, and a significant jump in the Moho depth was observed by the 2002 TRANSALP north–south profile. Here, a flip in subduction polarity has been suggested to occur. This dense network encompasses 163 stations and complements the larger-scale sparser AlpArray seismic network. The nominal station spacing in SWATH-D is 15 km in a high alpine, yet densely populated and industrialized region. We present here the challenges resulting from operating a large broadband network under these conditions and summarize how we addressed them, including the way we planned, deployed, maintained, and operated the stations in the field. Finally, we present some recommendations based on our experiences.

scholarly journals What seismicity offshore Sicily suggests about lithosphere dynamics and microplate fragmentation models in the Central Mediterranean

2018 ◽  
Author(s):  
Giancarlo Neri ◽  
Cristina Totaro ◽  
Barbara Orecchio ◽  
Debora Presti
Keyword(s):  
Waveform Inversion ◽  
Focal Mechanisms ◽  
Tectonic Deformation ◽  
Stress Distributions ◽  
Monitoring Networks ◽  
Central Mediterranean ◽  
Study Region ◽  
Seismic Waveform ◽  
Principal Axes ◽  
Sicily Channel

Abstract. We analyze an updated dataset of earthquakes of Southern Italy, focusing in particular on hypocenter locations and seismogenic stress distributions in the southern and eastearn offshores of Sicily, the two sectors of the study region where seismic and geodetic information needed for geodynamic modeling is still poor because of poor geometry of monitoring networks. Using Bayesian non-linear methods for hypocentral locations and hypocenter error estimates we improve the earthquake locations performed by more traditional linearized techniques, and this helps us to make significant progress in the interpretation of seismicity and seismogenic stress distributions especially where seismometric network geometry is more critical. Epicenter maps and hypocenter vertical sections, together with (i) best quality focal mechanisms coming from seismic waveform inversion and (ii) orientations of stress principal axes estimated by inversion of focal mechanisms, help us to better recognize geodynamic engines and plate margin deformation in the study area. NW-trending convergence between Africa and Eurasia is recognized as the main source of tectonic stress in the study region, producing clearly detectable signatures in terms of σ1 orientations also in the offshore sectors of the western Ionian and the Sicily Channel. Seismicity and seismogenic stress tensor highlight nearly uniform compressional dynamics related to plate convergence in the Sicily Channel, in contrast to rifting and microplate divergence proposed in that sector by other investigators. In the western Ionian, seismicity and stress inversion results reveal superposition of convergence-related compression and extensional dynamics. The latter, characterized by minimum compressive stress oriented SW-NE, can be related to a rifting process (opening SW-NE) hypothesized by previous investigators on the basis of marine geophysics analyses performed between the Alfeo-Etna and the Ionian Faults. The seismicity and seismogenic stress detected in the Western Ionian show that assumptions of microplate rigidity in this area made by previous workers when modeling poor geodetic data available can be inappropriate. Our findings indicate that more complex rheologic models should be adopted for reconstruction of tectonic deformation and microplate relative motions in the Central Mediterranean region.

scholarly journals GPS measurement of active strains across the Apennines

2012 ◽  
Vol 49 (1) ◽  
Author(s):  
Enrico Serpelloni ◽  
Marco Anzidei ◽  
Paolo Baldi ◽  
Giuseppe Casula ◽  
Alessandro Galvani
Keyword(s):  
Cross Sections ◽  
Time Interval ◽  
Strain Rates ◽  
Tyrrhenian Sea ◽  
Data Set ◽  
Active Deformation ◽  
Regional Deformation ◽  
Gps Measurement ◽  
Active Tectonic ◽  
Horizontal Strain

<p><span>Geodetic data are providing a new prospective in studying active tectonic processes that are occurring in penin- sular Italy. In this paper we use a recently published GPS velocity solution, obtained by merging a data set of permanent and non-permanent networks spanning the 1991-2002 time interval, to provide new quantitative con- straints of the active deformation rates across the Apennines Chain and the Calabrian Arc. The velocity field, given with respect to a fixed Eurasian frame, has been used to compute horizontal strain-rates within polygonal regions that connect and include geodetic stations, and to draw velocity cross sections along 5 different profiles through this region. The computed strain-rates provide a picture of the regional deformation field, which is in agreement with other seismological and geological data, and show that the Apennines are mainly extending in a SW-NE direction, while in Calabria extension is NW-SE oriented. Indications of active shortening are present only in the outer Northern Apennines. The velocity profiles across the Northern and Southern Apennines, along the Tyrrhenian Sea and Calabria, provide a quantitative measurement of the active extension and shortening rates, which are taking up at a more local scale. </span></p>

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