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

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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The 31 March 2020 Mw 6.5 Stanley, Idaho, Earthquake: Seismotectonics and Preliminary Aftershock Analysis

Seismological Research Letters ◽

10.1785/0220200319 ◽

2020 ◽

Author(s):

Lee M. Liberty ◽

Zachery M. Lifton ◽

T. Dylan Mikesell

Keyword(s):

Surface Displacement ◽

Volcanic Belt ◽

Normal Fault ◽

Fault System ◽

Basin And Range Province ◽

Ground Shaking ◽

The North ◽

Show Evidence ◽

Tectonic Framework ◽

Tectonic Belt

Abstract We report on the tectonic framework, seismicity, and aftershock monitoring efforts related to the 31 March 2020 Mw 6.5 Stanley, Idaho, earthquake. The earthquake sequence has produced both strike-slip and dip-slip motion, with minimal surface displacement or damage. The earthquake occurred at the northern limits of the Sawtooth normal fault. This fault separates the Centennial tectonic belt, a zone of active seismicity within the Basin and Range Province, from the Idaho batholith to the west and Challis volcanic belt to the north and east. We show evidence for a potential kinematic link between the northeast-dipping Sawtooth fault and the southwest-dipping Lost River fault. These opposing faults have recorded four of the five M≥6 Idaho earthquakes from the past 76 yr, including 1983 Mw 6.9 Borah Peak and the 1944 M 6.1 and 1945 M 6.0 Seafoam earthquakes. Geological and geophysical data point to possible fault boundary segments driven by pre-existing geologic structures. We suggest that the limits of both the Sawtooth and Lost River faults extend north beyond their mapped extent, are influenced by the relic trans-Challis fault system, and that seismicity within this region will likely continue for the coming years. Ongoing seismic monitoring efforts will lead to an improved understanding of ground shaking potential and active fault characteristics.

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Surface Faulting Caused by the 2016 Central Italy Seismic Sequence: Field Mapping and LiDAR/UAV Imaging

Earthquake Spectra ◽

10.1193/111417eqs236mr ◽

2018 ◽

Vol 34 (4) ◽

pp. 1585-1610 ◽

Cited By ~ 11

Author(s):

Stefano Gori ◽

Emanuela Falcucci ◽

Fabrizio Galadini ◽

Paolo Zimmaro ◽

Alberto Pizzi ◽

...

Keyword(s):

Imaging Techniques ◽

Central Italy ◽

Normal Fault ◽

Fault System ◽

Surface Rupture ◽

Field Mapping ◽

Central Italy Earthquake ◽

Levels Of Detail ◽

Main Fault ◽

Surface Ruptures

The three mainshock events (M6.1 24 August, M5.9 26 October, and M6.5 30 October 2016) in the Central Italy earthquake sequence produced surface ruptures on known segments of the Mt. Vettore–Mt. Bove normal fault system. As a result, teams from Italian national research institutions and universities, working collaboratively with the U.S. Geotechnical Extreme Events Reconnaissance Association (GEER), were mobilized to collect perishable data. Our reconnaissance approach included field mapping and advanced imaging techniques, both directed towards documenting the location and extent of surface rupture on the main fault exposure and secondary features. Mapping activity occurred after each mainshock (with different levels of detail at different times), which provides data on the progression of locations and amounts of slip between events. Along the full length of the Mt. Vettore–Mt. Bove fault system, vertical offsets ranged from 0–35 cm and 70–200 cm for the 24 August and 30 October events, respectively. Comparisons between observed surface rupture displacements and available empirical models show that the three events fit within expected ranges.

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Localized extension in megathrust hanging wall following great earthquakes in western Nepal

Scientific Reports ◽

10.1038/s41598-021-00297-4 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Magali Riesner ◽

Laurent Bollinger ◽

Judith Hubbard ◽

Cyrielle Guérin ◽

Marthe Lefèvre ◽

...

Keyword(s):

High Resolution ◽

Hanging Wall ◽

Ground Surface ◽

Normal Fault ◽

Fault Scarp ◽

Fault System ◽

Digital Elevation ◽

Thrust Zone ◽

Elevation Model ◽

Short Time

AbstractThe largest (M8+) known earthquakes in the Himalaya have ruptured the upper locked section of the Main Himalayan Thrust zone, offsetting the ground surface along the Main Frontal Thrust at the range front. However, out-of-sequence active structures have received less attention. One of the most impressive examples of such faults is the active fault that generally follows the surface trace of the Main Boundary Thrust (MBT). This fault has generated a clear geomorphological signature of recent deformation in eastern and western Nepal, as well as further west in India. We focus on western Nepal, between the municipalities of Surkhet and Gorahi where this fault is well expressed. Although the fault system as a whole is accommodating contraction, across most of its length, this particular fault appears geomorphologically as a normal fault, indicating crustal extension in the hanging wall of the MHT. We focus this study on the reactivation of the MBT along the Surkhet-Gorahi segment of the surface trace of the newly named Reactivated Boundary Fault, which is ~ 120 km long. We first generate a high-resolution Digital Elevation Model from triplets of high-resolution Pleiades images and use this to map the fault scarp and its geomorphological lateral variation. For most of its length, normal motion slip is observed with a dip varying between 20° and 60° and a maximum cumulative vertical offset of 27 m. We then present evidence for recent normal faulting in a trench located in the village of Sukhetal. Radiocarbon dating of detrital charcoals sampled in the hanging wall of the fault, including the main colluvial wedge and overlying sedimentary layers, suggest that the last event occurred in the early sixteenth century. This period saw the devastating 1505 earthquake, which produced ~ 23 m of slip on the Main Frontal Thrust. Linked or not, the ruptures on the MFT and MBT happened within a short time period compared to the centuries of quiescence of the faults that followed. We suggest that episodic normal-sense activity of the MBT could be related to large earthquakes rupturing the MFT, given its proximity, the sense of motion, and the large distance that separates the MBT from the downdip end of the locked fault zone of the MHT fault system. We discuss these results and their implications for the frontal Himalayan thrust system.

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A functional tool to explore the reliability of micro-earthquake focal mechanism solutions for seismotectonic purposes

Solid Earth ◽

10.5194/se-13-65-2022 ◽

2022 ◽

Vol 13 (1) ◽

pp. 65-83

Author(s):

Guido Maria Adinolfi ◽

Raffaella De Matteis ◽

Rita de Nardis ◽

Aldo Zollo

Keyword(s):

Focal Mechanism ◽

Fault Plane ◽

Normal Fault ◽

Focal Mechanisms ◽

Seismic Network ◽

Fault System ◽

Fault Plane Solutions ◽

Stress Regime ◽

Focal Mechanism Solutions ◽

Earthquake Focal Mechanism

Abstract. Improving the knowledge of seismogenic faults requires the integration of geological, seismological, and geophysical information. Among several analyses, the definition of earthquake focal mechanisms plays an essential role in providing information about the geometry of individual faults and the stress regime acting in a region. Fault plane solutions can be retrieved by several techniques operating in specific magnitude ranges, both in the time and frequency domain and using different data. For earthquakes of low magnitude, the limited number of available data and their uncertainties can compromise the stability of fault plane solutions. In this work, we propose a useful methodology to evaluate how well a seismic network, used to monitor natural and/or induced micro-seismicity, estimates focal mechanisms as a function of magnitude, location, and kinematics of seismic source and consequently their reliability in defining seismotectonic models. To study the consistency of focal mechanism solutions, we use a Bayesian approach that jointly inverts the P/S long-period spectral-level ratios and the P polarities to infer the fault plane solutions. We applied this methodology, by computing synthetic data, to the local seismic network operating in the Campania–Lucania Apennines (southern Italy) aimed to monitor the complex normal fault system activated during the Ms 6.9, 1980 earthquake. We demonstrate that the method we propose is effective and can be adapted for other case studies with a double purpose. It can be a valid tool to design or to test the performance of local seismic networks, and more generally it can be used to assign an absolute uncertainty to focal mechanism solutions fundamental for seismotectonic studies.

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Neotectonic and Paleoseismic Analysis of the Northwest Extent of Holocene Surface Deformation along the Meers Fault, Oklahoma

Bulletin of the Seismological Society of America ◽

10.1785/0120180148 ◽

2019 ◽

Vol 110 (1) ◽

pp. 49-66 ◽

Cited By ~ 1

Author(s):

Kristofer T. Hornsby ◽

Ashley R. Streig ◽

Scott E. K. Bennett ◽

Jefferson C. Chang ◽

Shannon Mahan

Keyword(s):

Surface Deformation ◽

Seismic Source ◽

Complex Surface ◽

Surface Expression ◽

Fault Scarp ◽

Source Characterization ◽

Surface Rupture ◽

Alluvial Deposits ◽

Aerial Photos ◽

Stable Continental Region

ABSTRACT The Meers fault (Oklahoma) is one of few seismogenic structures with evidence for Holocene surface rupture in the stable continental region of North America. The 37-kilometer-long southeast section of the full 54-kilometer-long Meers fault is interpreted to be Holocene active. The 17-kilometer-long northwest section is considered Quaternary active, but not Holocene active. We reevaluate surface expression and earthquake timing of the northwest Meers fault to improve seismic source characterization. We use airborne light detection and ranging and historical stereopaired aerial photos to evaluate the fault scarp and local fault-zone geomorphology. In the northwest, complex surface deformation includes fault splays, subtle monoclinal warping, and a minor change in fault strike. We interpret that the along-strike transition from surface faulting on the southeast Meers fault to surface folding on the northwest Meers fault occurs at the lithologic contact between Permian Post Oak conglomerate and Hennessey shale. We excavated a paleoseismic trench to evaluate the timing of surface-deforming earthquakes on the northwest section of the fault. The excavation revealed weathered Permian Hennessey shale and an ∼1–2-meter-thick veneer of Holocene alluvial deposits that were progressively deformed during two surface-folding earthquakes likely related to blind fault rupture beneath the site. Repeated onlapping to overlapping stratigraphic sequences and associated unconformities are intimately related to folding events along the monocline. OxCal paleoearthquake age modeling indicates that earthquakes occurred 4704–3109 yr B.P. and 5955–4744 yr B.P., and that part of the northwest section of the Meers fault is Holocene active. We find the Holocene-active section of the Meers fault should be lengthened 6.1 km to the northwest, to a total Holocene-active fault length of 43 km. Empirical scaling relationships between surface rupture length and magnitude reveal that the fault could generate an Mw 7.0 earthquake.

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Observations on normal-fault scarp morphology and fault system evolution of the Bishop Tuff in the Volcanic Tableland, Owens Valley, California, U.S.A.

Lithosphere ◽

10.1130/l476.1 ◽

2016 ◽

Vol 8 (3) ◽

pp. 238-253 ◽

Cited By ~ 7

Author(s):

David A. Ferrill ◽

Alan P. Morris ◽

Ronald N. McGinnis ◽

Kevin J. Smart ◽

Morgan J Watson-Morris ◽

...

Keyword(s):

Normal Fault ◽

Fault Scarp ◽

Fault System ◽

Bishop Tuff ◽

Owens Valley ◽

System Evolution ◽

Volcanic Tableland

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Rapid response to the Mw 4.9 earthquake of November 11, 2019 in Le Teil, Lower Rhône Valley, France

10.31219/osf.io/3afs5 ◽

2020 ◽

Author(s):

Cécile Cornou ◽

Jean-Paul Ampuero ◽

Coralie aubert ◽

Laurence Audin ◽

Stéphane Baize ◽

...

Keyword(s):

Focal Depth ◽

Seismic Hazard Assessment ◽

Normal Fault ◽

Field Evaluation ◽

Fault System ◽

Seismic Unit ◽

Epicentral Area ◽

Massif Central ◽

Moderate Seismicity ◽

Rhone Valley

On November 11, 2019, a Mw 4.9 earthquake hit the region close to Montelimar (lower Rhône Valley, France), on the eastern margin of the Massif Central close to the external part of the Alps. Occuring in a moderate seismicity area, this earthquake is remarkable for its very shallow focal depth (between 1 and 3 km), its magnitude, and the moderate to large damages it produced in several villages. InSAR interferograms indicated a shallow rupture about 4 km long reaching the surface and the reactivation of the ancient NE-SW La Rouviere normal fault in reverse faulting in agreement with the present-day E-W compressional tectonics. The peculiarity of this earthquake together with a poor coverage of the epicentral region by permanent seismological and geodetic stations triggered the mobilisation of the French post-seismic unit and the broad French scientific community from various institutions, with the deployment of geophysical instruments (seismological and geodesic stations), geological field surveys, and field evaluation of the intensity of the earthquake. Within 7 days after the mainshock, 47 seismological stations were deployed in the epicentral area to improve the Le Teil aftershocks locations relative to the French permanent seismological network (RESIF), monitor the temporal and spatial evolution of microearthquakes close to the fault plane and temporal evolution of the seismic response of 3 damaged historical buildings, and to study suspected site effects and their influence in the distribution of seismic damage. This seismological dataset, completed by data owned by different institutions, was integrated in a homogeneous archive and distributed through FDSN web services by the RESIF data center. This dataset, together with observations of surface rupture evidences, geologic, geodetic and satellite data, will help to unravel the causes and rupture mechanism of this earthquake, and contribute to account in seismic hazard assessment for earthquakes along the major regional Cévenne fault system in a context of present-day compressional tectonics.

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

Remote Sensing ◽

10.3390/rs13081555 ◽

2021 ◽

Vol 13 (8) ◽

pp. 1555

Author(s):

Rosa Nappi ◽

Valeria Paoletti ◽

Donato D’Antonio ◽

Francesco Soldovieri ◽

Luigi Capozzoli ◽

...

Keyword(s):

Seismic Tomography ◽

Active Faults ◽

Low Frequency ◽

Normal Fault ◽

Seismic Source ◽

Fault System ◽

Normal Faults ◽

Macroseismic Data ◽

Epicentral Area ◽

Seismogenic Source

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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A database of the environmental effects associated to the December 29th, 2020 Mw 6.4 Petrinja earthquake (Croatia)

10.5194/egusphere-egu21-16574 ◽

2021 ◽

Author(s):

Matija Vukovski ◽

Marko Budić ◽

Marko Špelić ◽

Josip Barbača ◽

Nikola Belić ◽

...

Keyword(s):

Environmental Effects ◽

Focal Depth ◽

Lateral Spreading ◽

Second Phase ◽

Surface Rupture ◽

Maximum Displacement ◽

Epicentral Area ◽

Ground Shaking ◽

Seismogenic Source ◽

Surface Ruptures

On December 29th, 2020, a strong Mw 6.4 earthquake hit central Croatia. The epicenter was located approximately 3 km southwest of Petrinja, and the intensity was estimated to VIII-IX EMS. The earthquake led to significant environmental effects related to earthquake magnitude, focal depth, and geological and geotechnical properties of the affected area. The Croatian Geological Survey (HGI-CGS) conducted extensive geological and geodetic surveys starting a few hours following the main shock to measure the earthquake&#8217;s effects, including those on infrastructures. Ten geologists from the Department of Geology carried out surveys from Decmber 31st, 2020 to January 7th, 2021 along the potential seismogenic source (inferred from geological maps and InSAR data) and in the wider epicentral area that suffered significant damage (e.g., Glina and Sisak). During a second phase, researchers from the University of Zagreb (PMF UniZG), Slovenia (GeoZS), Italy (INGV, ISPRA, U. Chieti) and France (CEREGE, IRSN) were mobilized to complete the observations. The collaboration with these geologists allowed to deepen the investigations and to bring further detail to quantify the effects. The surveys were then compiled based on data formats used by the European Community, namely those of the INGV EMERGEO team (Villani et al., 2017; for environmental effects including surface ruptures and liquefaction) and those of the SURE group (Baize et al., 2019 for surface ruptures). These observations revealed that the earthquake triggered a discontinuous, few km-long surface rupture with a maximum displacement of about 20 cm, which is consistent with the lower average of observations made on similar events (Wells and Coppersmith, 1994). Liquefaction spread over several tens of square kilometers mostly in river plains, the most distant being about 20 km from the epicenter (to be confirmed!). Other observed effects include lateral spreading, landslides, groundwater regime changes, rockfalls, and various infrastructure damage. The compilation of the acquired dataset into a unified database, consistent with database of other historical and recent events, is essential for establishing reliable empirical relations between geological effects and physical characteristics of earthquakes (magnitude, depth). This forms the basis for seismic hazard assessments, whether for &#8220;surface rupture&#8221;, &#8220;liquefaction&#8221;, or &#8220;ground-shaking&#8221; potential.

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Full characterization of the ML 5.4 2019/11/11 Le Teil earthquake in France based on a multi-technology approach

10.5194/egusphere-egu2020-9785 ◽

2020 ◽

Author(s):

Amaury Vallage ◽

Laurent Bollinger ◽

Yoann Cano ◽

Johann Champenois ◽

Clara Duverger ◽

...

Keyword(s):

Focal Mechanism ◽

Ground Deformation ◽

Waveform Inversion ◽

Normal Fault ◽

Fault System ◽

Tectonic Deformation ◽

Reverse Fault ◽

Ground Shaking ◽

Full Characterization ◽

Stable Continental Region

Metropolitan France is a region of slow tectonic deformation rates with sparse historical and instrumental seismicity, and where geodesy is not able to reach the required resolution in order to resolve the tectonic loadings. The few faults recognized as potential active rely on rare neotectonic slip rates, often integrated over geological scales.In this context, the ML&#160;5.4 Le Teil 2019 earthquake is of particular interest because it is the largest seismic event recorded in metropolitan France in the last 16 years. The last regional earthquake with a larger magnitude was the Lambesc event that occurred in 1909 about 110 km away from Le Teil epicenter. This recent earthquake offers a noteworthy opportunity to combine different technologies: seismological observations (RESIF and CEA) with satellite InSAR data and infrasound measurements, to help characterizing this stable continental region.The analysis shows that the focal mechanism determined from the full waveform inversion of long-period seismological data is consistent with the activation of a reverse fault with a strike around 45&#176;N and is associated with a moment magnitude of 4.8. Moreover, this event produced infrasound signals recorded by the OHP Alpine array located 110 km away. The analysis of these signals provides evidence of ground-to-air coupling in the epicentral region as well as ground shaking information.Despite the moderate magnitude of the event, the ground deformation is resolved by InSAR with Sentinel-1 data. The interferogram is consistent with the shallow depth inverted from seismology and confirmed by the presence of surface ruptures. The inversion of multiple InSAR tracks allows characterizing the displacement at depth and along strike on the fault plane. The results are consistent with the focal mechanism derived from seismology. The earthquake has ruptured a 5-km long by ~1.5-km deep fault. The displacement reaches a maximum at a shallow 1 km-depth. The source inverted from InSAR coincides with the Rouvi&#232;re fault, a branch of the C&#233;vennes fault system formerly known as a normal fault. This reverse earthquake might be an example of an inherited structure re-activation as it is often the case in intraplate regions with polyphased history.

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