New Insights into the Lake Erie Fault System from the 2019 ML 4.0 Ohio Earthquake Sequence

2021 ◽  
Author(s):  
Dongdong Yao ◽  
Yihe Huang ◽  
Jeffrey L. Fox
Keyword(s):  
Correlation Method ◽  
Earthquake Sequence ◽  
Fault System ◽  
Earthquake Catalog ◽  
Lake County ◽  
Local Seismicity ◽  
Linear Feature ◽  
Seismic Networks ◽  
Major Sequence ◽  
Seismic System

Abstract We present a detailed analysis of the 10 June 2019 ML 4.0 Ohio earthquake sequence, which is the largest earthquake that struck Lake County, northeastern Ohio, since 1986. This sequence is well recorded by local seismic networks, which provides an unprecedented opportunity to understand the local seismotectonics. We utilize a waveform-based cross-correlation method to identify ∼12 times more events than reported by the Advanced National Seismic System (ANSS) Comprehensive Earthquake Catalog: the whole sequence started with several small earthquakes (ML 1–2) beginning 12 March 2019, and the last one occurred ∼1min immediately before the ML 4.0 mainshock; many previously unreported aftershocks (ML 0.3–2.2) are found, which were active for the first week after the mainshock; another major sequence with a 7 December 2019 ML 2.6 mainshock occurred and also started with a few smaller events beginning in mid-November and was followed by its own aftershocks. The relocated seismicity delineates a linear feature, orientation of which is consistent with the resolved focal plane that may correspond to the ruptured fault. Our results highlight that closer monitoring of local seismicity is crucial for understanding the seismotectonics and mitigating future seismic hazard around the southern Great Lakes.

scholarly journals Machine-Learning-Based High-Resolution Earthquake Catalog Reveals How Complex Fault Structures Were Activated during the 2016–2017 Central Italy Sequence

2021 ◽  
Vol 1 (1) ◽  
pp. 11-19
Author(s):  
Yen Joe Tan ◽  
Felix Waldhauser ◽  
William L. Ellsworth ◽  
Miao Zhang ◽  
Weiqiang Zhu ◽  
...  
Keyword(s):  
Central Italy ◽  
Normal Fault ◽  
Earthquake Sequence ◽  
Fault System ◽  
Earthquake Catalog ◽  
Earthquake Triggering ◽  
Aftershock Activity ◽  
Arrival Times ◽  
Complex Fault ◽  
Fault Structures

Abstract The 2016–2017 central Italy seismic sequence occurred on an 80 km long normal-fault system. The sequence initiated with the Mw 6.0 Amatrice event on 24 August 2016, followed by the Mw 5.9 Visso event on 26 October and the Mw 6.5 Norcia event on 30 October. We analyze continuous data from a dense network of 139 seismic stations to build a high-precision catalog of ∼900,000 earthquakes spanning a 1 yr period, based on arrival times derived using a deep-neural-network-based picker. Our catalog contains an order of magnitude more events than the catalog routinely produced by the local earthquake monitoring agency. Aftershock activity reveals the geometry of complex fault structures activated during the earthquake sequence and provides additional insights into the potential factors controlling the development of the largest events. Activated fault structures in the northern and southern regions appear complementary to faults activated during the 1997 Colfiorito and 2009 L’Aquila sequences, suggesting that earthquake triggering primarily occurs on critically stressed faults. Delineated major fault zones are relatively thick compared to estimated earthquake location uncertainties, and a large number of kilometer-long faults and diffuse seismicity were activated during the sequence. These properties might be related to fault age, roughness, and the complexity of inherited structures. The rich details resolvable in this catalog will facilitate continued investigation of this energetic and well-recorded earthquake sequence.

Inversion of regional surface-wave spectra for source parameters of aftershocks from the 1992 Petrolia earthquake sequence

1995 ◽  
Vol 85 (3) ◽  
pp. 705-715
Author(s):  
Mark Andrew Tinker ◽  
Susan L. Beck
Keyword(s):  
Surface Wave ◽  
Focal Mechanism ◽  
Source Parameters ◽  
Strike Slip ◽  
Earthquake Sequence ◽  
Fault System ◽  
Accretionary Wedge ◽  
Wave Spectra ◽  
The North ◽  
Gorda Plate

Abstract Regional distance surface waves are used to study the source parameters for moderate-size aftershocks of the 25 April 1992 Petrolia earthquake sequence. The Cascadia subduction zone had been relatively seismically inactive until the onset of the mainshock (Ms = 7.1). This underthrusting event establishes that the southern end of the North America-Gorda plate boundary is seismogenic. It was followed by two separate and distinct large aftershocks (Ms = 6.6 for both) occurring at 07:41 and 11:41 on 26 April, as well as thousands of other small aftershocks. Many of the aftershocks following the second large aftershock had magnitudes in the range of 4.0 to 5.5. Using intermediate-period surface-wave spectra, we estimate focal mechanisms and depths for one foreshock and six of the larger aftershocks (Md = 4.0 to 5.5). These seven events can be separated into two groups based on temporal, spatial, and principal stress orientation characteristics. Within two days of the mainshock, four aftershocks (Md = 4 to 5) occurred within 4 hr of each other that were located offshore and along the Mendocino fault. These four aftershocks comprise one group. They are shallow, thrust events with northeast-trending P axes. We interpret these aftershocks to represent internal compression within the North American accretionary prism as a result of Gorda plate subduction. The other three events compose the second group. The shallow, strike-slip mechanism determined for the 8 March foreshock (Md = 5.3) may reflect the right-lateral strike-slip motion associated with the interaction between the northern terminus of the San Andreas fault system and the eastern terminus of the Mendocino fault. The 10 May aftershock (Md = 4.1), located on the coast and north of the Mendocino triple junction, has a thrust fault focal mechanism. This event is shallow and probably occurred within the accretionary wedge on an imbricate thrust. A normal fault focal mechanism is obtained for the 5 June aftershock (Md = 4.8), located offshore and just north of the Mendocino fault. This event exhibits a large component of normal motion, representing internal failure within a rebounding accretionary wedge. These two aftershocks and the foreshock have dissimilar locations in space and time, but they do share a north-northwest oriented P axis.

Active Faulting in Source Region of 2016–2017 Central Italy Event Sequence

2018 ◽  
Vol 34 (4) ◽  
pp. 1557-1583 ◽  
Author(s):  
Fabrizio Galadini ◽  
Emanuela Falcucci ◽  
Stefano Gori ◽  
Paolo Zimmaro ◽  
Daniele Cheloni ◽  
...  
Keyword(s):  
Source Region ◽  
Central Italy ◽  
Active Faults ◽  
Earthquake Sequence ◽  
Fault System ◽  
Fault Plane Solutions ◽  
Moment Tensors ◽  
Central Italy Earthquake ◽  
Finite Fault ◽  
Main Shocks

The Central Italy earthquake sequence produced three main shocks: M6.1 24 August, M5.9 26 October, and M6.5 30 October 2016. Additional M5–5.5 events struck this territory on 18 January 2017 in the Campotosto area. Fault plane solutions for the main shocks exhibit normal faulting (characteristic of crustal extension occurring in the inner central Apennines). Significant evidence, including hypocenter locations, strike and dip angles of the moment tensors, inverted finite fault models (using GPS, interferometric aperture radar, and ground motion data), and surface rupture patterns, all point to the earthquakes having been generated on the Mt. Vettore–Mt. Bove fault system (all three main shocks) and on the Amatrice fault, in the northern sector of the Laga Mountains (portion of 24 August event). The earthquake sequence provides examples of both synthetic and antithetic ruptures on a single fault system (30 October event) and rupture between two faults (24 August event). We describe active faults in the region and their segmentation and present understanding of the potential for linkages between segments (or faults) in the generation of large earthquakes.

A High-Resolution Seismic Catalog for the Initial 2019 Ridgecrest Earthquake Sequence: Foreshocks, Aftershocks, and Faulting Complexity

2020 ◽  
Vol 91 (4) ◽  
pp. 1971-1978 ◽  
Author(s):  
David R. Shelly
Keyword(s):  
High Resolution ◽  
Template Matching ◽  
Earthquake Sequence ◽  
Earthquake Catalog ◽  
Surface Rupture ◽  
Initial Portion ◽  
Multiple Fault ◽  
Fault Structures ◽  
Seismic Catalog ◽  
Complex Distribution

Abstract I use template matching and precise relative relocation techniques to develop a high-resolution earthquake catalog for the initial portion of the 2019 Ridgecrest earthquake sequence, from 4 to 16 July, encompassing the foreshock sequence and the first 10+ days of aftershocks following the Mw 7.1 mainshock. Using 13,525 routinely cataloged events as waveform templates, I detect and precisely locate a total of 34,091 events. Precisely located earthquakes reveal numerous crosscutting fault structures with dominantly perpendicular southwest and northwest strikes. Foreshocks of the Mw 6.4 event appear to align on a northwest-striking fault. Aftershocks of the Mw 6.4 event suggest that it further ruptured this northwest-striking fault, as well as the southwest-striking fault where surface rupture was observed. Finally, aftershocks of the Mw 7.1 show a highly complex distribution, illuminating a primary northwest-striking fault zone consistent with surface rupture but also numerous crosscutting southwest-striking faults. Aftershock relocations suggest that the Mw 7.1 event ruptured adjacent to the previous northwest-striking rupture of the Mw 6.4, perhaps activating a subparallel structure southwest of the earlier rupture. Both the northwest and southeast rupture termini of the Mw 7.1 rupture exhibited multiple fault branching, with particularly high rates of aftershocks and multiple fault orientations in the dilatational quadrant northeast of the northwest rupture terminus.

scholarly journals Deformation associated with sliver transport in Costa Rica: seismic and geodetic observations of the July 2016 Bijagua earthquake sequence

2019 ◽  
Vol 220 (1) ◽  
pp. 585-597 ◽  
Author(s):  
Maria C Araya ◽  
Juliet Biggs
Keyword(s):  
Surface Deformation ◽  
Ground Deformation ◽  
Surface Displacement ◽  
Strike Slip ◽  
Central American ◽  
Earthquake Sequence ◽  
Fault System ◽  
Aseismic Slip ◽  
Volcanic Arc ◽  
Forearc Sliver

SUMMARY Tectonic slivers form in the overriding plate in regions of oblique subduction. The inner boundaries of the sliver are often poorly defined and can consist of well-defined faults, rotating blocks or diffuse fault systems, which pass through or near the volcanic arc. The Guanacaste Volcanic Arc Sliver (GVAS) as defined by Montero et al., is a segment of the Central American Forearc Sliver, whose inner boundary is the ∼87-km-long Haciendas-Chiripa fault system (HCFS), which is located ∼10 km behind the volcanic arc and consists of strike slip faults and pull apart steps. We characterize the current ground motion on this boundary by combining earthquake locations and focal mechanisms of the 2016 Bijagua earthquake sequence, with the surface ground deformation obtained from Interferometric Synthetic Aperture Radar (InSAR) images from the ALOS-2 satellite. The coseismic stack of interferograms show ∼6 cm of displacement towards the line of sight of the satellite between the Caño Negro fault and the Upala fault, indicating uplift or SE horizontal surface displacement. The largest recorded earthquake of the sequence was Mw 5.4, and the observed deformation is one of the smallest earthquakes yet detected by InSAR in the Central American region. Forward and inverse models show the surface deformation can be partially explained by slip on a single fault, but it can be better explained by slip along two faults linked at depth. The best-fitting model consists of 0.33 m of right lateral slip on the Caño Negro fault and 0.35 m of reverse slip on the Upala fault, forming a positive flower structure. As no reverse seismicity was recorded, we infer the slip on the Upala fault occurred aseismically. Observations of the Bijagua earthquake sequence suggests the forearc sliver boundary is a complex and diffuse fault system. There are localized zones of transpression and transtension and areas where there is no surface expression suggesting the fault system is not yet mature. Although aseismic slip is common on subduction interfaces and mature strike-slip faults, this is the first study to document aseismic slip on a continental tectonic sliver boundary fault.

Effect of Combining Catalogs with Different Completeness

2020 ◽  
Author(s):  
Myunghyun Noh
Keyword(s):  
Korean Peninsula ◽  
North Korea ◽  
Seismic Network ◽  
The Other ◽  
Earthquake Catalog ◽  
Detection Capability ◽  
Chi Square ◽  
Earthquake Detection ◽  
Seismic Networks ◽  
Target Monitoring

<p>In most seismic studies, we prefer the earthquake catalog that covers a larger region and/or a longer period. We usually combine two or more catalogs to achieve this goal. When combining catalogs, however, care must be taken because their completeness is not identical so that unexpected flaws may be caused.</p><p>We tested the effect of combining inhomogeneous catalogs using the catalog of Korea Meteorological Administration (KMA). In fact, KMA provides a single catalog containing the earthquakes occurred in and around the whole Korean Peninsula. Like the other seismic networks, however, the configuration of the KMA seismic network is not uniform over its target monitoring region, so is the earthquake detection capability. The network is denser in the land than in the off-shore. Moreover, there are no seismic information available from North Korea. Based on these, we divided the KMA catalog into three sub-catalogs; SL, NL, and AO catalogs. The SL catalog contains the earthquakes occurred in the land of South Korea while the NL catalog contains those in the land of North Korea. The AO catalog contains all earthquakes occurred in the off-shore surrounding the peninsula.</p><p>The completeness of a catalog is expressed in terms of m<sub>c</sub>, the minimum magnitude above which no earthquakes are missing. We used the Chi-square algorithm by Noh (2017) to estimate the m<sub>c</sub>. It turned out, as expected, that the m<sub>c</sub> of the SL is the smallest among the three. Those of NL and AO are comparable. The m<sub>c</sub> of the catalog combining the SL and AO is larger than those of individual catalogs before combining. The m<sub>c</sub> is largest when combining all the three. If one needs more complete catalog, he or she had better divide the catalog into smaller ones based on the spatiotemporal detectability of the seismic network. Or, one may combine several catalogs to cover a larger region or a longer period at the expense of catalog completeness.</p>

scholarly journals Seismic and Geodetic Crustal Moment-Rates Comparison: New Insights on the Seismic Hazard of Egypt

2021 ◽  
Vol 11 (17) ◽  
pp. 7836
Author(s):  
Rashad Sawires ◽  
José A. Peláez ◽  
Federica Sparacino ◽  
Ali M. Radwan ◽  
Mohamed Rashwan ◽  
...  
Keyword(s):  
Active Regions ◽  
Seismic Source ◽  
Satellite System ◽  
Dead Sea ◽  
Fault System ◽  
Gulf Of Aqaba ◽  
Seismic Sources ◽  
Earthquake Catalog ◽  
Focal Mechanism Solutions ◽  
Rate Ratios

A comparative analysis of geodetic versus seismic moment-rate estimations makes it possible to distinguish between seismic and aseismic deformation, define the style of deformation, and also to reveal potential seismic gaps. This analysis has been performed for Egypt where the present-day tectonics and seismicity result from the long-lasting interaction between the Nubian, Eurasian, and Arabian plates. The data used comprises all available geological and tectonic information, an updated Poissonian earthquake catalog (2200 B.C.–2020 A.D.) including historical and instrumental datasets, a focal-mechanism solutions catalog (1951–2019), and crustal geodetic strains from Global Navigation Satellite System (GNSS) data. The studied region was divided into ten (EG-01 to EG-10) crustal seismic sources based mainly on seismicity, focal mechanisms, and geodetic strain characteristics. The delimited seismic sources cover the Gulf of Aqaba–Dead Sea Transform Fault system, the Gulf of Suez­–Red Sea Rift, besides some potential seismic active regions along the Nile River and its delta. For each seismic source, the estimation of seismic and geodetic moment-rates has been performed. Although the obtained results cannot be considered to be definitive, among the delimited sources, four of them (EG-05, EG-06, EG-08, and EG-10) are characterized by low seismic-geodetic moment-rate ratios (<20%), reflecting a prevailing aseismic behavior. Intermediate moment-rate ratios (from 20% to 60%) have been obtained in four additional zones (EG-01, EG-04, EG-07, and EG-09), evidencing how the seismicity accounts for a minor to a moderate fraction of the total deformational budget. In the other two sources (EG-02 and EG-03), high seismic-geodetic moment-rates ratios (>60%) have been observed, reflecting a fully seismic deformation.

scholarly journals Tsunami hazard in Lombok & Bali, Indonesia, due to the Flores backarc thrust

2021 ◽  
Author(s):  
Raquel Felix ◽  
Judith Hubbard ◽  
Kyle Bradley ◽  
Karen Lythgoe ◽  
Linlin Li ◽  
...  
Keyword(s):  
Maximum Flow ◽  
Tsunami Hazard ◽  
Earthquake Sequence ◽  
Coastal Hazards ◽  
Fault System ◽  
Northern Coast ◽  
Coseismic Slip ◽  
Ground Shaking ◽  
Tsunami Waves ◽  
Earthquake Scenarios

Abstract. The tsunami hazard posed by the Flores backarc thrust, which runs along the northern coast of the islands of Bali and Lombok, Indonesia, is poorly studied compared to the Sunda megathrust, situated ~250 km to the south of the islands. However, the 2018 Lombok earthquake sequence demonstrated the seismic potential of the western Flores Thrust when a fault ramp beneath the island of Lombok ruptured in two Mw 6.9 earthquakes. Although the uplift in these events mostly occurred below land, the sequence still generated 1–2.5 m-high local tsunamis along the northern coast of Lombok (Wibowo et al., 2021). Historical records show that the Flores fault system in the Lombok and Bali region has generated at least six ≥ Ms 6.5 tsunamigenic earthquakes since 1800 CE. Hence, it is important to assess the possible tsunami hazard represented by this fault system. Here, we focus on the submarine fault segment located between the islands of Lombok and Bali (below the Lombok Strait). We assess modeled tsunami patterns generated by fault slip in six earthquake scenarios (slip of 1–5 m, representing Mw 7.2–7.9+), with a focus on impacts on the capital cities of Mataram, Lombok and Denpasar, Bali, which lie on the coasts facing the strait. We use a geologically constrained earthquake model informed by the Lombok earthquake sequence (Lythgoe et al., 2021), together with a high-resolution bathymetry dataset developed by combining direct measurements from GEBCO with sounding measurements from the official nautical charts for Indonesia. Our results show that fault rupture in this region could trigger a tsunami reaching Mataram in < 8 minutes and Denpasar in ~10–15 minutes, with multiple waves. For an earthquake with 3–5 m of coseismic slip, Mataram and Denpasar experience maximum wave heights of ~1.3–3.3 m and ~0.7 to 1.5 m, respectively. Furthermore, our earthquake models indicate that both cities would experience coseismic subsidence of 20–40 cm, exacerbating their exposure to both the tsunami and other coastal hazards. Overall, Mataram city is more exposed than Denpasar to high tsunami waves arriving quickly from the fault source. To understand how a tsunami would affect Mataram, we model the associated inundation using the 5 m slip model and show that Mataram is inundated ~55–140 m inland along the northern coast and ~230 m along the southern coast, with maximum flow depths of ~2–3 m. Our study highlights that the early tsunami arrival in Mataram, Lombok gives little time for residents to evacuate. Raising their awareness about the potential for locally generated tsunamis and the need for evacuation plans is important to help them respond immediately after experiencing strong ground shaking.

Seismogenic Faults of the Changning Earthquake Sequence Constrained by High-Resolution Seismic Profiles in the Southwestern Sichuan Basin, China

2021 ◽  
Author(s):  
Renqi Lu ◽  
Dengfa He ◽  
Jing-Zeng Liu ◽  
Wei Tao ◽  
Hanyu Huang ◽  
...  
Keyword(s):  
High Resolution ◽  
Sichuan Basin ◽  
Structural Characteristics ◽  
Sedimentary Cover ◽  
Earthquake Sequence ◽  
Fault System ◽  
Unstable State ◽  
Induced Earthquakes ◽  
Seismicity Rate ◽  
Seismogenic Faults

Abstract The seismicity rate in the southwestern Sichuan basin, China, dramatically increased after 2014. The associated moderate earthquakes may have been induced by salt mining or shale gas exploration. The location of the seismogenic faults causing these moderate earthquakes has not been confirmed, resulting in a lack of understanding of the earthquake mechanisms in the study area. The detailed structural characteristics of pre-existing faults, which are typically responsible for induced seismicity, are unclear. In this study, we used high-resolution seismic reflection profiles in conjunction with geological, seismologic, and geodetic data to reveal the 3D distributions of the seismogenic faults. Basement thrust faults in the Changning anticline were identified using seismic interpretations and are associated with the 2019 Changning earthquake sequence. The geometry and location of these pre-existing faults are consistent with previous studies of the seismology and structural geology in the area. The well-developed pre-existing fault system in the sedimentary cover and basement makes the Changning area vulnerable to induced earthquakes. Present-day reactivation of the basement fault system reveals the unstable state of the local tectonic stress field. It is possible that the potential seismic risk in this region could be increased by industrial activity in the southwestern Sichuan basin.

Seismotectonic Snapshots: The 18 March 2020 Mw 5.7 Magna, 31 March 2020 Mw 6.5 Stanley, and 15 May 2020 Mw 6.5 Monte Cristo Intermountain West Earthquakes

2021 ◽  
Author(s):  
Steven G. Wesnousky
Keyword(s):  
Active Faults ◽  
Relative Size ◽  
Fault System ◽  
Intermountain West ◽  
Surface Rupture ◽  
Slip Mechanism ◽  
Walker Lane ◽  
Earthquake Ruptures ◽  
Seismic Networks ◽  
Broad Region

Abstract Seismological characteristics of the 18 March 2020 Mw 5.7 Magna, 31 March 2020 Mw 6.5 Stanley, and 15 May 2020 Mw 6.5 Monte Cristo Intermountain West earthquakes are largely consistent with expectations arising from observations accumulated over the ∼40  yr since implementation and subsequent growth of seismic networks in the broad region. Each occurred within a zone of relatively elevated seismicity, active faults, and geodetically observed strain accumulation. Aftershock distributions in each are confined primarily to depths of &lt;15  km, and the total number of aftershocks correlates with the relative size of the events. In each case, the number per day decays exponentially in the days following the mainshock. None of the mainshocks was preceded by a foreshock sequence that delivered a plausible warning of the impending earthquakes. With respect to tectonics, each earthquake brings new insights. The Stanley and Monte Cristo earthquakes are at the margins of geodetically defined regions of right-lateral transtension, though the pattern of faulting in each region is markedly different. The strike-slip mechanism of the Stanley earthquake stands in contrast to the zone of normal major range bounding faults and historical earthquake ruptures that characterize the region in which it occurred and is the first relatively well instrumented event to show a rupture extending northward through the Trans-Challis fault system. The Magna event has been interpreted to represent low-angle normal slip near the base of a listric Wasatch range bounding fault (Pang et al., 2020). The east-striking left-lateral Monte Cristo earthquake within the Walker Lane is in contrast to the major northwest-striking right-lateral faults that dominate the area, though predictable from prior regional mapping. Surface rupture reportedly accompanied only the Monte Cristo earthquake, though its trace does not clearly follow the zone of aftershocks.

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