Joint Interpretation of Geophysical Results and Geological Observations for Detecting Buried Active Faults: The Case of the “Il Lago” Plain (Pettoranello del Molise, Italy)

We report a geophysical study across an active normal fault in the Southern Apennines. The surveyed area is the “Il Lago” Plain (Pettoranello del Molise), at the foot of Mt. Patalecchia (Molise Apennines, Southern Italy), a small tectonic basin filled by Holocene deposits located at the NW termination of the major Quaternary Bojano basin structure. This basin, on the NE flank of the Matese Massif, was the epicentral area of the very strong 26 July, 1805, Sant’Anna earthquake (I0 = X MCS, Mw = 6.7). The “Il Lago” Plain is bordered by a portion of the right-stepping normal fault system bounding the whole Bojano Quaternary basin (28 km long). The seismic source responsible for the 1805 earthquake is regarded as one of the most hazardous structures of the Apennines; however, the position of its NW boundary of this seismic source is debated. Geological, geomorphological and macroseismic data show that some coseismic surface faulting also occurred in correspondence with the border fault of the “Il Lago” Plain. The study of the “Il Lago” Plain subsurface might help to constrain the NW segment boundary of the 1805 seismogenic source, suggesting that it is possibly a capable fault, source for moderate (Mw < 5.5) to strong earthquakes (Mw ≥ 5.5). Therefore, we constrained the geometry of the fault beneath the plain using low-frequency Ground Penetrating Radar (GPR) data supported by seismic tomography. Seismic tomography yielded preliminary information on the subsurface structures and the dielectric permittivity of the subsoil. A set of GPR parallel profiles allowed a quick and high-resolution characterization of the lateral extension of the fault, and of its geometry at depth. The result of our study demonstrates the optimal potential of combined seismic and deep GPR surveys for investigating the geometry of buried active normal faults. Moreover, our study could be used for identifying suitable sites for paleoseismic analyses, where record of earthquake surface faulting might be preserved in Holocene lacustrine sedimentary deposits. The present case demonstrates the possibility to detect with high accuracy the complexity of a fault-zone within a basin, inferred by GPR data, not only in its shallower part, but also down to about 100 m depth.

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Evaluation of macroseismic intensity, strong ground motion pattern and fault model of the 19 July 2019 Mw5.1 earthquake west of Athens

Journal of Seismology ◽

10.1007/s10950-021-09990-3 ◽

2021 ◽

Author(s):

V. Kouskouna ◽

A. Ganas ◽

M. Kleanthi ◽

I. Kassaras ◽

N. Sakellariou ◽

...

Keyword(s):

Ground Motion ◽

Normal Fault ◽

Macroseismic Intensity ◽

Fault System ◽

Joint Analysis ◽

Macroseismic Data ◽

Rupture Directivity ◽

Epicentral Area ◽

Time Histories ◽

The One

AbstractThis paper presents a joint analysis of instrumental and macroseismic data regarding the 19 July 2019, Greece Mw5.1 earthquake occurred west of Athens. This earthquake ruptured a blind, south-dipping normal fault, 23 km WNW of the center of Athens, while its relocated epicentre lies in close vicinity to the one of the 1999 Mw6.0 earthquake. The maximum macroseismic intensity of the 2019 mainshock reached IEMS98 = 7.5. Scarce damage and intensities up to 5–6 were reported in the epicentral area. Higher intensities were observed at larger distances, 12–15 km east and ESE of the epicentre, alongside the banks of Kifissos River, likely related to ground motion amplification due to soft alluvial formations. Similar selectivity of increased ground motions to the east of the epicentre with respect to other azimuths, also observed during the 1981 and 1999 earthquakes, supports eastward rupture directivity of the 2019 mainshock, an effect that is possibly common for the region’s fault system. Damping of seismic effects was observed east of Aegaleo Mountain, a structure suggested to impose a stopping phase in the time histories of the 1999 and 2019 earthquakes (Fig. A1).

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Neogene-Quaternary tectonic regime and macroseismic observations in the Tyrnavos-Elassona broader epicentral area of the March 2021, intense earthquake sequence

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.27196 ◽

2021 ◽

Vol 58 ◽

pp. 200

Author(s):

Dimitrios Galanakis ◽

Sotiris Sboras ◽

Garyfalia Konstantopoulou ◽

Markos Xenakis

Keyword(s):

Normal Fault ◽

Fault Scarp ◽

Focal Mechanisms ◽

Fault System ◽

Spatiotemporal Evolution ◽

Surface Rupture ◽

Alluvial Deposits ◽

Epicentral Area ◽

Ground Shaking ◽

Macroseismic Observations

On March 3, 2021, a strong (Mw6.3) earthquake occurred near the towns of Tyrnavos and Elassona. One day later (March 4), a second strong (Mw6.0) earthquake occurred just a few kilometres toward the WNW. The aftershock spatial distribution and the focal mechanisms revealed NW-SE-striking normal faulting. The focal mechanisms also revealed a NE-SW oriented extensional stress field, different from the orientation we knew so far (ca. N-S). The magnitude and location of the two strongest shocks, and the spatiotemporal evolution of the sequence, strongly suggest that two adjacent fault segments were ruptured respectively. The sequence was followed by several coseismic ground deformational phenomena, such as landslides/rockfalls, liquefaction and ruptures. The landslides and rockfalls were mostly associated with the ground shaking. The ruptures were observed west of the Titarissios River, near to the Quaternary faults found by bore-hole lignite investigation. In the same direction, a fault scarp separating the alpidic basement from the alluvial deposits of the Titarissios valley implies the occurrence of a well-developed fault system. Some of the ground ruptures were accompanied by extensive liquefaction phenomena. Others cross-cut reinforced concrete irrigation channels without changing their direction. We suggest that this fault system was partially reactivated, as a secondary surface rupture, during the sequence as a steeper splay of a deeper low-to-moderate angle normal fault.

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Methodology for Earthquake Rupture Rate estimates of fault networks: example for the Western Corinth Rift, Greece

10.5194/nhess-2017-124 ◽

2017 ◽

Cited By ~ 1

Author(s):

Thomas Chartier ◽

Oona Scotti ◽

Hélène Lyon-Caen ◽

Aurélien Boiselet

Keyword(s):

Active Faults ◽

Slip Rate ◽

Seismic Hazard Assessment ◽

System Level ◽

Fault System ◽

Normal Faults ◽

Accurate Estimation ◽

Probabilistic Seismic Hazard Assessment ◽

Earthquake Rupture ◽

Multiple Faults

Abstract. Modelling the seismic potential of active faults is a fundamental step of probabilistic seismic hazard assessment (PSHA). An accurate estimation of the rate of earthquakes on the faults is necessary in order to obtain the probability of exceedance of a given ground motion. Most PSHA studies consider faults as independent structures and neglect the possibility of multiple faults or fault segments rupturing simultaneously (Fault to Fault -FtF- ruptures). The latest Californian model (UCERF-3) takes into account this possibility by considering a system level approach rather than an individual fault level approach using the geological , seismological and geodetical information to invert the earthquake rates. In many places of the world seismological and geodetical information long fault networks are often not well constrained. There is therefore a need to propose a methodology relying only on geological information to compute earthquake rate of the faults in the network. In this methodology, similarly to UCERF-3, a simple distance criteria is used to define FtF ruptures and consider single faults or FtF ruptures as an aleatory uncertainty. Rates of earthquakes on faults are then computed following two constraints: the magnitude frequency distribution (MFD) of earthquakes in the fault system as a whole must follow an imposed shape and the rate of earthquakes on each fault is determined by the specific slip-rate of each segment depending on the possible FtF ruptures. The modelled earthquake rates are then confronted to the available independent data (geodetical, seismological and paleoseismological data) in order to weigh different hypothesis explored in a logic tree. The methodology is tested on the Western Corinth Rift, Greece (WCR) where recent advancements have been made in the understanding of the geological slip rates of the complex network of normal faults which are accommodating the ~15 mm/yr North-South extension. Modelling results show that geological, seismological extension rates and paleoseismological rates of earthquakes cannot be reconciled with only single fault rupture scenarios and require hypothesising a large spectrum of possible FtF rupture sets. Furthermore, in order to fit the imposed regional Gutenberg-Richter MFD target, some of the slip along certain faults needs to be accommodated either with interseismic creep or as post-seismic processes. Furthermore, individual fault’s MFDs differ depending on the position of each fault in the system and the possible FtF ruptures associated with the fault. Finally, a comparison of modelled earthquake rupture rates with those deduced from the regional and local earthquake catalogue statistics and local paleosismological data indicates a better fit with the FtF rupture set constructed with a distance criteria based on a 5 km rather than 3 km, suggesting, a high connectivity of faults in the WCR fault system.

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Identifikasi Sesar Aktif di Pulau Bali dengan Menggunakan Data Pemetaan Geologi Permukaan dan Morfologi Tektonik

Majalah Geografi Indonesia ◽

10.22146/mgi.61928 ◽

2021 ◽

Vol 35 (1) ◽

pp. 45

Author(s):

Hurien Helmi ◽

Gayatri Indah Marliyani ◽

Siti Nur’aini

Keyword(s):

Hazard Analysis ◽

Active Faults ◽

Fault System ◽

Normal Faults ◽

Earthquake Hazards ◽

Digital Elevation ◽

Shallow Earthquakes ◽

Lineament Analysis ◽

Elevation Model ◽

Back Arc

Pulau Bali dan sekitarnya berada dekat dengan zona subduksi sehingga rawan terhadap bencana gempa bumi. Struktur utama yang menyebabkan gempa bumi di Bali umumnya berada di zona subduksi di bagian selatan dan di zona sesar naik belakang busur di utara yang dikenal dengan sesar naik Flores. Selain potensi gempa dari kedua zona sesar ini, gempa yang berasal dari zona sesar di darat juga bisa menimbulkan bahaya yang signifikan. Penelitian ini bertujuan untuk melakukan pemetaan sesar aktif di darat dengan menggunakan kombinasi antara metode penginderaan jauh dengan survey lapangan. Data yang digunakan sebagai peta dasar adalah data digital elevation (DEM) model DEMNAS beresolusi 8 m serta data DEM beresolusi 0.5 m yang dihasilkan melalui proses fotogrametri dari foto udara. Analisis kelurusan menunjukkan adanya pola berarah baratlaut-tenggara dan timulaut-baratdaya. Validasi di lapangan menunjukkan bahwa kelurusan ini berasosiasi dengan keberadaan sesar-sesar geser, sesar oblique dan sesar turun. Sesar-sesar ini memotong batuan berumur Kuarter hingga endapan masa kini. Selain itu, data sebaran seismisitas menunjukkan adanya zona kegempaan dangkal yang berada pada area di sekitar kelurusan yang dipetakan. Kedua indikator ini menunjukkan bahwa sesar-sesar yang teridentifikasi dalam penelitian ini bisa dikategorikan sebagai sesar aktif. Hasil dari penelitian ini memberikan pemahaman baru mengenai geometri sesar aktif yang ada di Pulau Bali dan potensi kegempaan di masa yang akan datang yang memberikan kontribusi terhadap upaya mitigasi bencana gempa bumi di Pulau Bali. Bali and its surrounding region are located within proximity of the Sunda-Banda subduction zone making it prone to earthquake hazards. The structures that caused earthquakes in Bali are mainly from the front subduction faults and from the back-arc thrust fault known as the Flores Fault. In addition, earthquakes are frequently occur in the inland fault system. This study aims to map the inland active faults in Bali using a combination of remotely-based and field-mapping methods. We use the 8-m resolution digital elevation model (DEM) of DEMNAS and the 0.5 m resolution DEM from photogrammetry processing of aerial photo as our base maps. Our lineament analysis identifies northwest-southeast and northeast-southwest lineaments. Our field observation confirms these lineaments to be associated with strike-slip, oblique and normal faults. These faults dissect Quarternary to recent rock units. In addition, seismicity data indicate the occurrence of shallow earthquakes in the vicinity of these structures. All of these indicate that these structures are active. Results from this study provide a new understanding of the inland active fault geometry in Bali, useful in the seismic hazard analysis and may contribute to the earthquake mitigation efforts in Bali.

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Segmentation of the Wassuk Range normal fault system, Nevada (USA): Implications for earthquake rupture and Walker Lane dynamics

Geological Society of America Bulletin ◽

10.1130/b35756.1 ◽

2021 ◽

Author(s):

Ben Surpless ◽

Sarah Thorne

Keyword(s):

Seismic Hazard Assessment ◽

Normal Fault ◽

Relative Strength ◽

Fault System ◽

Normal Faults ◽

Slip Rates ◽

Future Evolution ◽

Walker Lane ◽

Differential Uplift ◽

Wassuk Range

Normal faults are commonly segmented along strike, with segments that localize strain and influence propagation of slip during earthquakes. Although the geometry of segments can be constrained by fault mapping, it is challenging to determine seismically relevant segments along a fault zone. Because slip histories, geometries, and strengths of linkages between normal fault segments fundamentally control the propagation of rupture during earthquakes, and differences in segment slip rates result in differential uplift of adjacent footwalls, we used along-strike changes in footwall morphology to detect fault segments and the relative strength of the mechanical links between them. We applied a new geomorphic analysis protocol to the Wassuk Range fault, Nevada, within the actively deforming Walker Lane. The protocol examines characteristics of footwall morphology, including range-crest continuity, bedrock-channel long profiles, catchment area variability, and footwall relief, to detect changes in strike-parallel footwall characteristics. Results revealed six domains with significant differences in morphology that we used to identify seismically relevant fault segments and segment boundaries. We integrated our results with previous studies to determine relative strength of links between the six segments, informing seismic hazard assessment. When combined with recent geodetic studies, our results have implications for the future evolution of the Walker Lane, suggesting changes in the accommodation of strain across the region. Our analysis demonstrates the power of this method to efficiently detect along-strike changes in footwall morphology related to fault behavior, permitting future researchers to perform reconnaissance assessment of normal fault segmentation worldwide.

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Multiple Lines of Evidence for a Potentially Seismogenic Fault Along the Central-Apennine (Italy) Active Extensional Belt–An Unexpected Outcome of the MW6.5 Norcia 2016 Earthquake

Frontiers in Earth Science ◽

10.3389/feart.2021.642243 ◽

2021 ◽

Vol 9 ◽

Author(s):

Federica Ferrarini ◽

Rita de Nardis ◽

Francesco Brozzetti ◽

Daniele Cirillo ◽

J Ramón Arrowsmith ◽

...

Keyword(s):

Late Quaternary ◽

Tectonic Setting ◽

Central Italy ◽

Stress Transfer ◽

Normal Fault ◽

Normal Faults ◽

Coulomb Stress ◽

Seismic Sequence ◽

Seismogenic Fault ◽

Seismogenic Source

The Apenninic chain, in central Italy, has been recently struck by the Norcia 2016 seismic sequence. Three mainshocks, in 2016, occurred on August 24 (MW6.0), October 26 (MW 5.9) and October 30 (MW6.5) along well-known late Quaternary active WSW-dipping normal faults. Coseismic fractures and hypocentral seismicity distribution are mostly associated with failure along the Mt Vettore-Mt Bove (VBF) fault. Nevertheless, following the October 26 shock, the aftershock spatial distribution suggests the activation of a source not previously mapped beyond the northern tip of the VBF system. In this area, a remarkable seismicity rate was observed also during 2017 and 2018, the most energetic event being the April 10, 2018 (MW4.6) normal fault earthquake. In this paper, we advance the hypothesis that the Norcia seismic sequence activated a previously unknown seismogenic source. We constrain its geometry and seismogenic behavior by exploiting: 1) morphometric analysis of high-resolution topographic data; 2) field geologic- and morphotectonic evidence within the context of long-term deformation constraints; 3) 3D seismological validation of fault activity, and 4) Coulomb stress transfer modeling. Our results support the existence of distributed and subtle deformation along normal fault segments related to an immature structure, the Pievebovigliana fault (PBF). The fault strikes in NNW-SSE direction, dips to SW and is in right-lateral en echelon setting with the VBF system. Its activation has been highlighted by most of the seismicity observed in the sector. The geometry and location are compatible with volumes of enhanced stress identified by Coulomb stress-transfer computations. Its reconstructed length (at least 13 km) is compatible with the occurrence of MW≥6.0 earthquakes in a sector heretofore characterized by low seismic activity. The evidence for PBF is a new observation associated with the Norcia 2016 seismic sequence and is consistent with the overall tectonic setting of the area. Its existence implies a northward extent of the intra-Apennine extensional domain and should be considered to address seismic hazard assessments in central Italy.

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Multidisciplinary analyses for mapping and evaluating kinematics and stress/strain field at active faults and fissures at NE Rift, Mt Etna (Italy)

10.5194/egusphere-egu21-4279 ◽

2021 ◽

Author(s):

Susanna Falsaperla ◽

Alessandro Tibaldi ◽

Noemi Corti ◽

Emanuela De Beni ◽

Fabio L. Bonali ◽

...

Keyword(s):

Active Faults ◽

Normal Fault ◽

Structural Data ◽

Field Work ◽

Normal Faults ◽

Extension Rate ◽

Mt Etna ◽

Hazardous Zone ◽

Eruptive Fissures ◽

Ne Rift

Strategies for disaster risk reduction in volcanic areas are mostly driven by multidisciplinary analyses, which offer effective and complementary information on complex geomorphological and volcano-tectonic environments. For example, quantification of the offset at active faults and fissures is of paramount importance to shed light on the kinematics of zones prone to deformation and/or seismic activity. This provides key information for the assessment of seismic hazard, but also for the identification of conditions that may favor magma uprising and opening of eruptive fissures.Here we present the results of a study encompassing detailed geological, structural and seismological observations focusing on part of the NE Rift at Etna volcano (Italy). The area is situated at an elevation ranging between 2700 and 1900 m a.s.l. where harsh meteorological conditions and difficult logistics render classical field work a troublesome issue. In order to bypass these difficulties, high-resolution (2.8 cm) UAV survey has been recently completed. The survey highlights the presence of 250 extension fractures, 20 normal fault segments, and 54 eruptive fissures. The study allows us to quantify the kinematics at extensional fractures and normal faults, obtaining an extension rate of 1.9 cm/yr for the last 406 yr. With a total of 432 structural data collected by UAV along with SfM photogrammetry, this work also demonstrates the suitability of the application of such surveys for the monitoring of hazardous zone.

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Pore-pressure migration along a normal-fault system resolved by time-repeated seismic tomography

Geology ◽

10.1130/g25220a.1 ◽

2009 ◽

Vol 37 (1) ◽

pp. 67-70 ◽

Cited By ~ 28

Author(s):

Claudio Chiarabba ◽

Pasquale De Gori ◽

Enzo Boschi

Keyword(s):

Pore Pressure ◽

Seismic Tomography ◽

Normal Fault ◽

Fault System

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Structural characterization of fault damage zones in carbonates (Central Apennines, Italy)

10.5194/egusphere-egu21-1525 ◽

2021 ◽

Author(s):

Miriana Chinello ◽

Michele Fondriest ◽

Giulio Di Toro

Keyword(s):

Fault Zone ◽

Hanging Wall ◽

Damage Zone ◽

Normal Fault ◽

Vertical Displacement ◽

Fault System ◽

Normal Faults ◽

Central Apennines ◽

Fault Surface ◽

Fracture Intensity

The Italian Central Apennines are one of the most seismically active areas in the Mediterranean (e.g., L&#8217;Aquila 2009, Mw 6.3 earthquake). The mainshocks and the aftershocks of these earthquake sequences propagate and often nucleate in fault zones cutting km-thick limestones and dolostones formations. An impressive feature of these faults is the presence, at their footwall, of few meters to hundreds of meters thick damage zones. However, the mechanism of formation of these damage zones and their role during (1) individual seismic ruptures (e.g., rupture arrest), (2) seismic sequences (e.g., aftershock evolution) and (3) seismic cycle (e.g., long term fault zone healing) are unknown. This limitation is also due to the lack of knowledge regarding the distribution, along strike and with depth, of damage with wall rock lithology, geometrical characteristics (fault length, inherited structures, etc.) and kinematic properties (cumulative displacement, strain rate, etc.) of the associated main faults.Previous high-resolution field structural surveys were performed on the Vado di Corno Fault Zone, a segment of the ca. 20 km long Campo Imperatore normal fault system, which accommodated ~ 1500 m of vertical displacement (Fondriest et al., 2020). The damage zone was up to 400 m thick and dominated by intensely fractured (1-2 cm spaced joints) dolomitized limestones with the thickest volumes at fault oversteps and where the fault cuts through an older thrust zone. Here we describe two minor faults located in the same area (Central Apennines), but with shorter length along strike. They both strike NNW-SSE and accommodated a vertical displacement of ~300 m.The Subequana Valley Fault is about 9 km long and consists of multiple segments disposed in an en-echelon array. The fault juxtaposes pelagic limestones at the footwall and quaternary deposits at the hanging wall. The damage zone is < 25 m &#160;thick &#160;and comprises fractured (1-2 cm spaced joints) limestones beds with decreasing fracture intensity moving away from the master fault. However, the damage zone thickness increases up to &#8764;100 m in proximity of subsidiary faults striking NNE-SSW. The latter could be reactivated inherited structures.The Monte Capo di Serre Fault is about 8 km long and characterized by a sharp ultra-polished master fault surface which cuts locally dolomitized Jurassic platform limestones. The damage zone is up to 120 m thick and cut by 10-20 cm spaced joints, but it reaches an higher fracture intensity where is cut by subsidiary, possibly inherited, faults striking NNE-SSW.Based on these preliminary observations, faults with similar displacement show comparable damage zone thicknesses. The most relevant damage zone thickness variations are related to geometrical complexities rather than changes in lithology (platform vs pelagic carbonates). &#160;In particular, the largest values of damage zone thickness and fracture intensity occur at fault overstep or are associated to inherited structures. The latter, by acting as strong or weak barriers (sensu Das and Aki, 1977) during the propagation of seismic ruptures, have a key role in the formation of damage zones and the growth of normal faults.

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Potentially active normal faulting zone identified in the eastern margin of Palu City, Central Sulawesi, Indonesia

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/873/1/012071 ◽

2021 ◽

Vol 873 (1) ◽

pp. 012071

Author(s):

Anggraini Rizkita Puji ◽

Mudrik Rahmawan Daryono ◽

Danny Hilman Natawidjaja

Keyword(s):

Active Faults ◽

Digital Terrain Model ◽

Slip Rate ◽

Normal Fault ◽

Provincial Government ◽

Economic Losses ◽

Normal Faults ◽

Normal Faulting ◽

Eastern Margin ◽

Central Sulawesi

Abstract The 2018 Mw 7.5 earthquake in Palu, Central Sulawesi, resulting in ~2,000 fatalities and estimated economic losses of ~22.8 trillion Indonesian Rupiah, according to the report of BAPPENAS and Central Sulawesi Provincial-Government. Therefore, it is necessary to prevent similar disaster in the future by further detailed studies of any other potential sources that are capable of generating such hazards. Palu City is in the vast depression valley bordered by mountains in its eastern and western margins. The 2018 earthquake source is the Palukoro Fault, which runs through the western margin of onshore Palu Valley then continued under the bay. Along the eastern margin of the valley, we also identified a wide zone of many potentially active faults strands orienting N-S and NW-SE, showing predominantly normal faulting. These faults are observed from their normal fault scarps as inspected from Light Detection and Ranging Digital Terrain Model (LiDAR DTM) data with 90-cm resolution and field ground checks. The faults deformed the old terrace sediments (Late Pleistocene, ~125 kya), but it is unclear whether they also cut the Holocene young alluvial like the ruptured fault of 2018 event. Further paleoseismology investigation is then necessary to obtain further information about these potentially-active normal faults, including their slip-rate and the past ruptures.

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