Insights into seismic activity of Central Adriatic offshore (Italy) evidenced by the 2013-2014, Conero seismic sequence

2021 ◽  
Author(s):  
Guido Maria Adinolfi ◽  
Elvira Battimelli ◽  
Ortensia Amoroso ◽  
Paolo Capuano
Keyword(s):  
Seismic Activity ◽  
Adriatic Sea ◽  
Probabilistic Approach ◽  
Active Faults ◽  
Hydrocarbon Exploration ◽  
P Wave ◽  
Seismic Sequence ◽  
Borehole Data ◽  
Fault Plane Solutions ◽  
Orogenic Belts

<p>The Adriatic region has always attracted the interests of researchers involved in the study of the tectonic processes that controlled the evolution of the Alpine-Mediterranean area. It has been considered as an undeformed area, an aseismic, rigid block located between two active orogenic belts, the Apennines and External Dinarides thrust belts. Nevertheless, new scientific evidences reveal a complex structural framework in which active faults are capable to produce seismic activity not only along the borders of Adriatic Sea, but also in the offshore areas. In fact, the outer thrusts of Apennines and Dinarides orogenic belts propagated from the coasts to the offshore areas originating active, NW-SE trending anticlines and thrust faults that affects the Plio-Quaternary sequences.</p><p>Defining the seismotectonics of Adriatic domain and studying the active tectonics of the area with its seismogenic potential represent a challenge because the sea prevents direct observation of main geological and structural lineaments and the deployment of standard seismic networks for a more accurate analysis of seismicity. Despite the existence of new evidences, derived from seismic profiles and borehole data, by hydrocarbon exploration, correct seismic hazard estimates of Adriatic Sea require original and accurate data on the seismic activity that can allow to depict the number, size and geometry of seismogenic sources.</p><p>In this work, we focused our attention on the seismic sequence, consisting of about 230 events,  which occurred along the Central Adriatic coast, in the Conero offshore, during the 2013-2104, with a M<sub>L</sub> 4.9 mainshock located at 20 km far away from city of Ancona, the main city of Marche region. After a careful and innovative selection of the data recorded from the Italian National Seismic Network, operated by the Istituto Nazionale di Geofisica e Vulcanologia, the earthquakes were relocated according to a probabilistic approach. By the inversion of the polarity of the P-wave first arrivals, the focal mechanisms were estimated and finally the local magnitudes were re-calculated. Moreover, in order verify if there has been a migration of seismicity with the activation of different faults during the seismic sequence, the analysis of spatio-temporal evolution of the seismic sequence was performed. Preliminary results show that the seismic sequence was originated mainly at small depths (< 10 km) along NW-SE trending thrust fault structures as evidenced by fault plane solutions, consistent with NE-SW horizontal, maximum compression of the outer front of Apennines thrust belt, still active in the Central Adriatic offshore.</p>

scholarly journals Structural complexities and tectonic barriers controlling recent seismic activity of the Pollino area (Calabria-Lucania, Southern Italy) – constraints from stress inversion and 3D fault model building

2021 ◽  
Author(s):  
Daniele Cirillo ◽  
Cristina Totaro ◽  
Giusy Lavecchia ◽  
Barbara Orecchio ◽  
Rita de Nardis ◽  
...  
Keyword(s):  
Seismic Activity ◽  
Model Building ◽  
Fault Model ◽  
P Wave ◽  
Fault System ◽  
Double Difference ◽  
Seismic Sequence ◽  
High Angle ◽  
Time Space ◽  
Seismological Data

Abstract. The integration of field geology and high-resolution seismological data allowed us to reconstruct the 3D Fault Model of the sources which gave rise to the 2010–2014 Pollino seismic sequence. The model is constrained at the surface by structural geological data which provide the true attitude of the single faults and their cross-cut relationships. At depth, the fault geometry was obtained using the distributions of selected high-quality relocated hypocenters. Relocations were carried out through a non-linear Bayloc algorithm, followed by the double-difference relative location method HypoDD, applied to a 3D P-wave velocity model. Geological and seismological data converge in describing an asymmetric active extensional fault system characterized by an E to NNE-dipping low-angle detachment, with its high-angle synthetic splays, and SW- to WSW-dipping, high-angle antithetic faults. The cluster of hypocenters and the peculiar time-space evolution of the seismic activity highlight that two sub-parallel WSW-dipping seismogenic sources, namely the Rotonda-Campotenese and Morano-Piano di Ruggio faults activated during the seismic crisis. By applying to the activated structures the appropriate earthquake-scaling relationships, based on fault length and fault area, we infer that the maximum expected magnitudes calculated using the fault area are the more reliable. We estimated Mw = 6.4 for the Rotonda-Campotenese and Mw = 6.2 for the Morano-Piano di Ruggio deducing that both the faults did not release their seismic potential during the 2010–2014 seismic sequence. The size of the activated patches, reconstructed by projecting on the 3D seismogenic fault planes the early aftershocks of the seismicity clusters, are consistent with the observed magnitude of the associate strongest events. Finally, we point out that the western segment of the Pollino Fault, despite not being presently active, acts as a barrier to the southern propagation of the Rotonda-Campotenese and Morano-Piano di Ruggio faults, limiting their dimensions and seismogenic potential.

scholarly journals Present-day stress state in northwestern Syria

2020 ◽  
Vol 59 (4) ◽  
pp. 299-316
Author(s):  
Mohamad Khir Abdul-Wahed ◽  
Mohammed ALISSA
Keyword(s):  
Fault Plane ◽  
Eastern Mediterranean ◽  
Active Faults ◽  
Plate Boundary ◽  
Shear Zones ◽  
Stress Pattern ◽  
P Wave ◽  
Fault System ◽  
Fault Plane Solutions ◽  
Stress Regime

Northwestern Syria is a key area in the eastern Mediterranean to study the active tectonics and stress pattern across the Arabia-Eurasia convergent plate boundary. This study aims to outline the present-day stress regime in this region of Syria using the fault plane solutions of the largest events recorded by the Syrian National Seismological Network from 1995 to 2011. A dataset of fault-plane solutions was obtained for 48 events having at least 5 P-wave polarities. The tectonic regime for most of these events is extensional and produces normal mechanisms in agreement with the local configurations of the seismogenic faults in the region. Strike-slip mechanisms are more scarce and restricted to certain areas, such as the northern extension of the Dead Sea fault system. The results of the current study reveal the spatial variations of SHmax orientation across the northwestern Syria region. This spatial variation of the present-day stress field highlights the role of main geometrically complex shear zones in the present-day stress pattern of northwestern Syria. However, these results show, regardless of the relatively small magnitudes of the studied events, they provide a picture of the local stress deviations that have currently been taking place along the local active faults.

Seismic velocity-depth relation in foreland basins: the case study of the Central Adriatic Sea

2020 ◽  
Author(s):  
Vittorio Scisciani ◽  
Paolo Mancinelli
Keyword(s):  
Adriatic Sea ◽  
Seismic Velocity ◽  
Vertical Component ◽  
Foreland Basin ◽  
Hydrocarbon Exploration ◽  
Foreland Basins ◽  
Seismic Profiles ◽  
Borehole Data ◽  
Geophysical Processes ◽  
Stratigraphic Evolution

<p>In the frame of the geological characterization of the subsurface, the multidisciplinary approach is key to fully understand the geological and geophysical processes. Seismic data analysis and interpretation would result in a mere exercise without constraints provided by geological, geophysical and petrophysical data. These constraints may be provided by borehole data, surface geology or laboratory measurements on samples. In this work, to support geological understanding of foreland basins we integrate reprocessed seismic profiles and borehole data in the Central Adriatic Sea to investigate the velocity-depth trend of the Pliocene-Quaternary turbiditic siliciclastic deposits. These deposits play a key role in the reconstruction of the geodynamic and stratigraphic evolution of the foreland basin, as well as on the hydrocarbon exploration and gas storage in central Adriatic. Relying on independent approaches to map two way time (TWT) thickness of the PH deposits, we converge on testing linear and exponential functions to predict V<sub>P</sub> depth trend. Results suggest that for large (> 1500 m) thicknesses of the PH deposits best fit is achieved by the exponential function V<sub>P</sub>(z) = c z<sup>(1-n)</sup> while for thinner deposits, a linear function like V<sub>P</sub>(z) = V<sub>0</sub> + k z provides best fitting estimates. We also investigate anomalies in velocity trend with depth and suggest that velocity drops observed in deep (2500-3500 m) PH sequences may reflect overpressure of these deposits. An hypothesis supported by the high sedimentation rates in central Adriatic during Pliocene. Finally, we stress the importance of considering vertical-component phenomena and their time evolution when modelling foreland basins.</p>

Seismic Activity in the Central Adriatic Offshore of Italy: A Review of the 1987 ML 5 Porto San Giorgio Earthquake

2019 ◽  
Author(s):  
Elvira Battimelli ◽  
Guido Maria Adinolfi ◽  
Ortensia Amoroso ◽  
Paolo Capuano
Keyword(s):  
Probabilistic Approach ◽  
Active Faults ◽  
Velocity Model ◽  
Gas Production ◽  
Seismic Sequence ◽  
Velocity Models ◽  
Geological Features ◽  
Seismogenic Faults ◽  
Intensity Field ◽  
Hypocentral Location

ABSTRACT On 3 July 1987, a seismic sequence, with a mainshock of ML 5, took place in the offshore Adriatic, close to the coast of Porto San Giorgio (PSG), Italy. We present an accurate relocation of the PSG seismic sequence using a nonlinear probabilistic approach (Lomax et al., 2000). The trade‐off between the hypocentral location and the velocity model was exhaustively explored using six different velocity models available for the area provided by previous studies. Through numerous tests performed by relocating the mainshock, we selected the two best velocity models providing two different depths (2.0 and 18.0 km). To resolve this intrinsic ambiguity, we developed a technique that uses the macroseismic intensity field data based on a grid search of the magnitude–depth space. The results show that the mainshock has a depth of 5.7 km and a magnitude (ML) equal to 5; moreover, the relocated seismic sequence (∼30 events) developed in the upper portion of the crust (at a depth less than 15 km), thus activating thrust faults, which is typical of the main geological features that characterize the outer Apennines thrust belt and the Adriatic foreland folds. Because the Adriatic Sea hosts several hydrocarbon (mainly gas) production fields located near active faults, with some of them in the area of this study, analyzing the instrumental seismicity is necessary to better understand the seismicity generated by these seismogenic faults and improve the assessment of the area’s seismic hazards.

scholarly journals Contemporary stress field in the area of the 2016 Amatrice seismic sequence (central Italy)

2016 ◽  
Vol 59 ◽  
Author(s):  
Maria Teresa Mariucci ◽  
Paola Montone
Keyword(s):  
Stress Field ◽  
Empirical Relationship ◽  
Central Italy ◽  
Local Stress ◽  
P Wave ◽  
Seismic Sequence ◽  
Borehole Data ◽  
Rock Density ◽  
Deep Wells ◽  
Sonic Logs

We update the last present-day stress map for Italy relatively to the area of 2016 Amatrice seismic sequence (central Italy) taking into account a large number of earthquakes occurred from August 24 to October 3, 2016. In particular in this paper, we discuss the new stress data from crustal earthquake focal mechanisms selecting those with Magnitude ≥ 4.0; at the same time, we revise the borehole data, analyze the stratigraphic profiles and the relative sonic logs in 4 deep wells located close to the Amatrice sequence along the Apennine belt and toward east along the Adriatic foredeep. From these data we consider the P-wave velocity trend with depth and estimate rock density following an empirical relationship. Then we calculate the overburden stress magnitude for each well. The new present-day stress indicators confirm the presence of prevalent normal faulting regime and better define the local stress field in the area, highlighting a slight rotation from NE-SW to ENE-WSW of extension. The analysis evidences that the lithostatic gradient gradually changes from ~26 MPa/km in the belt to less than 23 MPa/km along the Adriatic foredeep. Finally, at a depth of 5 km we estimate the vertical stress magnitude varying from 130 MPa to 114 moving from the Apennine belt to the Adriatic foredeep. Although the wells are very close each other they show different P wave velocities from the belt to the foredeep with values ~7km/s and ~4 km/s at 5 km depth, respectively.

Liquefaction susceptibility maps for the Aqaba–Elat region with projections of future hazards with sea-level rise

2020 ◽  
pp. qjegh2020-039 ◽  
Author(s):  
Abdel-Rahman A. Abueladas ◽  
Tina M. Niemi ◽  
Abdallah Al-Zoubi ◽  
Gideon Tibor ◽  
Mor Kanari ◽  
...  
Keyword(s):  
Sea Level ◽  
Water Table ◽  
Active Faults ◽  
Gulf Of Aqaba ◽  
Susceptibility Map ◽  
Northern Coast ◽  
Borehole Data ◽  
Ground Acceleration ◽  
Liquefaction Susceptibility ◽  
Susceptibility Maps

The cities of Aqaba, Jordan and Elat, Israel are vulnerable to seismic damage because they are built over the active faults of the Dead Sea Transform that are the source of historically destructive earthquakes. A liquefaction susceptibility map was generated for the Aqaba–Elat region. Borehole data from 149 locations and the water table depth were used to calculate effective overburden stress in the Seed–Idriss simplified method. The liquefaction analysis was based on applying a cyclic loading scenario with horizontal peak ground acceleration of 0.3 g in a major earthquake. The liquefaction map, compiled using a GIS platform, shows high and moderate liquefaction susceptibility zones along the northern coast of the Gulf of Aqaba that extend 800 m inland from the shoreline. In Aqaba, several hotels, luxury apartment complexes, archaeological sites, ports and commercial districts are located within high and moderate liquefaction zones. In Elat, the seaport and the coastal hotel district are located within a high susceptibility zone. Most residential areas, schools and hospitals in both cities are located within zones not susceptible to liquefaction based on the methods of this study. The total area with the potential to be liquefied along the Gulf of Aqaba is c. 10 km2. Given predictions for global sea-level, we ran three liquefaction models utilizing projected water table rises of 0.5, 1 and 2 m. These models yielded an increase in the area of high liquefaction ranging from 26 to 49%. Given the high potential of future earthquakes, our liquefaction susceptibility maps should help inform city officials for hazard mitigation planning.

Aftershocks of the February 21, 1973 Point Mugu, California earthquake

1976 ◽  
Vol 66 (6) ◽  
pp. 1931-1952
Author(s):  
Donald J. Stierman ◽  
William L. Ellsworth
Keyword(s):  
Fault Zone ◽  
Main Shock ◽  
Fault Plane ◽  
Body Wave ◽  
P Wave ◽  
Fault System ◽  
Wave Radiation ◽  
Fault Plane Solutions ◽  
Complex Deformation ◽  
Transverse Ranges

abstract The ML 6.0 Point Mugu, California earthquake of February 21, 1973 and its aftershocks occurred within the complex fault system that bounds the southern front of the Transverse Ranges province of southern California. P-wave fault plane solutions for 51 events include reverse, strike slip and normal faulting mechanisms, indicating complex deformation within the 10-km broad fault zone. Hypocenters of 141 aftershocks fail to delineate any single fault plane clearly associated with the main shock rupture. Most aftershocks cluster in a region 5 km in diameter centered 5 km from the main shock hypocenter and well beyond the extent of fault rupture estimated from analysis of body-wave radiation. Strain release within the imbricate fault zone was controlled by slip on preexisting planes of weakness under the influence of a NE-SW compressive stress.

The 2019 Ms 4.2 and 5.2 Beiliu Earthquake Sequence in South China: Complex Conjugate Strike-Slip Faulting Revealed by Rupture Directivity Analysis

2021 ◽  
Author(s):  
Xiaohui He ◽  
Hao Liang ◽  
Peizhen Zhang ◽  
Yue Wang
Keyword(s):  
South China ◽  
Source Parameters ◽  
Active Faults ◽  
Fault Zones ◽  
Strike Slip ◽  
P Wave ◽  
Complex Conjugate ◽  
South China Block ◽  
Rupture Directivity ◽  
Time Duration

Abstract The South China block has been one of the most seismically quiescent regions in China, and the geometries and activities of the Quaternary faults have remained less studied due to the limited outcrops. Thus, source parameters of small-to-moderate earthquakes are important to help reveal the location, geometry distribution, and mechanical properties of the subsurface faults and thus improve the seismic risk assessment. On 12 October 2019, two earthquakes (the Ms 4.2 foreshock and the Ms 5.2 mainshock) occurred within 2 s and are located in southern South China block, near the junction region of the large-scale northeast-trending fault zones and the less continuous northwest-trending fault zones. We determined the point-source parameters of the two events via P-wave polarity analysis and regional waveform modeling, and the resolved focal mechanisms are significantly different with the minimum 3D rotation angle of 52°. We then resolved the rupture directivity of the two events by analyzing the azimuth variation of the source time duration and found the Ms 4.2 foreshock ruptured toward north-northwest for ∼1.0 km, and the Ms 5.2 mainshock ruptured toward east-southeast (ESE) for ∼1.5 km, implying conjugate strike-slip faulting. The conjugate causative faults have not been mapped on the regional geological map, and we infer that the two faults may be associated with the northwest-trending Bama-Bobai fault zone (the Shiwo section). These active faults are optimally oriented in the present-day stress field (northwest-southeast) and thus may now be potentially accumulating elastic strain to be released in a future large earthquake.

A reality check on full-wave inversion applied to land seismic data for near-surface modeling

2022 ◽  
Vol 41 (1) ◽  
pp. 40-46
Author(s):  
Öz Yilmaz ◽  
Kai Gao ◽  
Milos Delic ◽  
Jianghai Xia ◽  
Lianjie Huang ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Seismic Data ◽  
Surface Modeling ◽  
P Wave ◽  
Borehole Data ◽  
Near Surface ◽  
Traveltime Tomography ◽  
Wave Inversion ◽  
Full Wave ◽  
Elastic Inversion

We evaluate the performance of traveltime tomography and full-wave inversion (FWI) for near-surface modeling using the data from a shallow seismic field experiment. Eight boreholes up to 20-m depth have been drilled along the seismic line traverse to verify the accuracy of the P-wave velocity-depth model estimated by seismic inversion. The velocity-depth model of the soil column estimated by traveltime tomography is in good agreement with the borehole data. We used the traveltime tomography model as an initial model and performed FWI. Full-wave acoustic and elastic inversions, however, have failed to converge to a velocity-depth model that desirably should be a high-resolution version of the model estimated by traveltime tomography. Moreover, there are significant discrepancies between the estimated models and the borehole data. It is understandable why full-wave acoustic inversion would fail — land seismic data inherently are elastic wavefields. The question is: Why does full-wave elastic inversion also fail? The strategy to prevent full-wave elastic inversion of vertical-component geophone data trapped in a local minimum that results in a physically implausible near-surface model may be cascaded inversion. Specifically, we perform traveltime tomography to estimate a P-wave velocity-depth model for the near-surface and Rayleigh-wave inversion to estimate an S-wave velocity-depth model for the near-surface, then use the resulting pairs of models as the initial models for the subsequent full-wave elastic inversion. Nonetheless, as demonstrated by the field data example here, the elastic-wave inversion yields a near-surface solution that still is not in agreement with the borehole data. Here, we investigate the limitations of FWI applied to land seismic data for near-surface modeling.

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