Lake Charles, Louisiana, earthquake of 16 October 1983

1988 ◽  
Vol 78 (4) ◽  
pp. 1463-1474
Author(s):  
Donald A. Stevenson ◽  
James D. Agnew
Keyword(s):  
Gulf Coast ◽  
Normal Fault ◽  
Velocity Model ◽  
Strike Slip ◽  
Crystalline Basement ◽  
P Wave ◽  
Normal Faulting ◽  
Significant Evidence ◽  
Lake Charles ◽  
East West

Abstract On 16 October 1983, at 19:40 (UTC), a magnitude 3.8 earthquake occurred near Lake Charles in southwestern Louisiana. The earthquake was felt over an area of 2600 km2 and had a maximum Modified Mercalli intensity of V. This was the first significant Louisiana Gulf Coast earthquake to be recorded and located by nearby microseismic networks. One possible foreshock and three aftershocks also were recorded and located using a velocity model developed for this study. The focal mechanism of the earthquake was determined based on P-wave first motions from 22 local and regional stations. The solution indicates a predominantly east-west trending, southeast-dipping normal fault with a small strike-slip component. The depth of this event (14+ km) provides the first significant evidence that normal faulting within the crystalline basement may control shallower growth faults along the Gulf Coast.

A teleseismic body-wave analysis of the May 1980 Mammoth Lakes, California, earthquakes

1983 ◽  
Vol 73 (2) ◽  
pp. 419-434
Author(s):  
Jeffery S. Barker ◽  
Charles A. Langston
Keyword(s):  
Body Wave ◽  
Moment Tensor ◽  
Normal Fault ◽  
Strike Slip ◽  
Body Waves ◽  
P Wave ◽  
Moment Tensors ◽  
Double Couple ◽  
The Moment ◽  
Mammoth Lakes

abstract Teleseismic P-wave first motions for the M ≧ 6 earthquakes near Mammoth Lakes, California, are inconsistent with the vertical strike-slip mechanisms determined from local and regional P-wave first motions. Combining these data sets allows three possible mechanisms: a north-striking, east-dipping strike-slip fault; a NE-striking oblique fault; and a NNW-striking normal fault. Inversion of long-period teleseismic P and SH waves for the events of 25 May 1980 (1633 UTC) and 27 May 1980 (1450 UTC) yields moment tensors with large non-double-couple components. The moment tensor for the first event may be decomposed into a major double couple with strike = 18°, dip = 61°, and rake = −15°, and a minor double couple with strike = 303°, dip = 43°, and rake = 224°. A similar decomposition for the last event yields strike = 25°, dip = 65°, rake = −6°, and strike = 312°, dip = 37°, and rake = 232°. Although the inversions were performed on only a few teleseismic body waves, the radiation patterns of the moment tensors are consistent with most of the P-wave first motion polarities at local, regional, and teleseismic distances. The stress axes inferred from the moment tensors are consistent with N65°E extension determined by geodetic measurements by Savage et al. (1981). Seismic moments computed from the moment tensors are 1.87 × 1025 dyne-cm for the 25 May 1980 (1633 UTC) event and 1.03 × 1025 dyne-cm for the 27 May 1980 (1450 UTC) event. The non-double-couple aspect of the moment tensors and the inability to obtain a convergent solution for the 25 May 1980 (1944 UTC) event may indicate that the assumptions of a point source and plane-layered structure implicit in the moment tensor inversion are not entirely valid for the Mammoth Lakes earthquakes.

scholarly journals A reappraisal of active tectonics along the Fethiye-Burdur trend, southwestern Turkey

2021 ◽  
Author(s):  
Edwin Nissen ◽  
Mussaver Didem Cambaz ◽  
Élyse Gaudreau ◽  
Andrew Howell ◽  
Ezgi Karasözen ◽  
...  
Keyword(s):  
Active Tectonics ◽  
Normal Fault ◽  
Recent Change ◽  
Strike Slip ◽  
Gravitational Potential Energy ◽  
Normal Faults ◽  
Normal Faulting ◽  
Arrival Times ◽  
Anatolian Plateau ◽  
Recent Earthquakes

We investigate active tectonics in southwestern Turkey along the trend between Fethiye, near the eastern end of the Hellenic subduction zone, and Burdur, on the Anatolian plateau. Previously, regional GPS velocity data have been used to propose either (1) a NE-trending zone of strike-slip faulting coined the Fethiye-Burdur Fault Zone, or (2) a mix of uniaxial and radial extension accommodated by normal faults with diverse orientations. We test these models against the available earthquake data, updated in light of recent earthquakes at Acıpayam (20 March 2019, Mw 5.6) and Bozkurt (8 August 2019, Mw 5.8) — the largest in this region in the last two decades — and at Arıcılar (24 November 2017, Mw 5.3). Using Sentinel-1 InSAR and seismic waveforms and arrival times, we show that the Acıpayam, Bozkurt and Arıcılar earthquakes were buried ruptures on pure normal faults with subtle or indistinct topographic expressions. By exploiting ray paths shared with these well-recorded modern events, we relocate earlier instrumental seismicity throughout southwestern Turkey. We find that the 1971 Mw 6.0 Burdur earthquake likely ruptured a NW-dipping normal fault in an area of indistinct geomorphology near Salda Lake, contradicting earlier studies that place it on well-expressed faults bounding the Burdur basin. Overall, the northern Fethiye-Burdur trend is characterized by orthogonal normal faulting, consistent with radial extension and likely responsible for the distinct physiography of Turkey's 'Lake District'. The southern Fethiye-Burdur trend is dominated by ESE-WNW trending normal faulting, even though most faults evident in the topography strike NE-SW. This hints at a recent change in regional strain, perhaps related to eastward propagation of the Gökova graben into the area or to rapid subsidence of the Rhodes basin. Overall, our results support GPS-derived tectonic models that depict a mix of uniaxial and radial extension throughout southwestern Turkey, with no evidence for major, active strike-slip faults anywhere along the Fethiye-Burdur trend. Normal faulting orientations are consistent with a stress field driven primarily by contrasts in gravitational potential energy between the elevated Anatolian plateau and the low-lying Rhodes and Antalya basins.

The July 2020 Mw 6.3 Nima Earthquake, Central Tibet: A Shallow Normal-Faulting Event Rupturing in a Stepover Zone

2021 ◽  
Author(s):  
Jiuyuan Yang ◽  
Caijun Xu ◽  
Yangmao Wen ◽  
Guangyu Xu
Keyword(s):  
Normal Fault ◽  
Strike Slip ◽  
Deformation Analysis ◽  
Postseismic Deformation ◽  
Integrated Analysis ◽  
Tectonic Deformation ◽  
Normal Faulting ◽  
Coseismic Slip ◽  
Synthetic Aperture Radar Data ◽  
Central Tibet

Abstract On 22 July 2020, an Mw 6.3 earthquake with a predominantly normal-faulting mechanism struck the Yibug Caka fault zone, central Tibet, where the overall tectonic environment is characterized by left-lateral strike-slip motion. This event offers a chance to gain insight into the tectonic deformation and the cause of shallow normal-faulting earthquakes in this little studied region. Here, we use Sentinel-1A/B Interferometric Synthetic Aperture Radar data to investigate the coseismic and postseismic deformation related to this earthquake. The earthquake ruptured a previously mapped West Yibug Caka fault and is dominated by normal slip with a peak value of 1.9 m at depth of 6.9 km. Postseismic deformation analysis indicates that the observed subsidence signals of up to ∼4.7 cm are a consequence of afterslip. Most of the afterslip is confined at depths between 0.8 and 8.4 km, peaking at 0.27 m at depth of 6.1 km. The significant coseismic slip and afterslip involved in the earthquake highlights a complex interaction between the major normal fault and the secondary synthetic fault. By an integrated analysis of the inversions, regional geology geomorphology, fault kinematics, and seismicity background, we propose a tectonic model that attributes the occurrence of this normal-faulting event to the release of extensional stress in a stepover zone controlled by the northeast-striking sinistral strike-slip Riganpei Co fault and Bu Zang Ai fault. Compared with that the structural stepover often acts as a barrier to affect the propagation of earthquake rupture, our study demonstrates that the failure of a stepover may potentially induce the occurrence of earthquake along the bounding strike-slip faults.

scholarly journals Earthquakes in Switzerland and surrounding regions during 2017 and 2018

2021 ◽  
Vol 114 (1) ◽  
Author(s):  
Tobias Diehl ◽  
John Clinton ◽  
Carlo Cauzzi ◽  
Toni Kraft ◽  
Philipp Kästli ◽  
...  
Keyword(s):  
Ground Motions ◽  
Structural Complexity ◽  
Normal Fault ◽  
Strike Slip ◽  
Crystalline Basement ◽  
Border Region ◽  
Thrust Faulting ◽  
Fold And Thrust Belt ◽  
Aar Massif ◽  
Alpine Foreland

AbstractThis report summarizes the seismicity in Switzerland and surrounding regions in the years 2017 and 2018. In 2017 and 2018, the Swiss Seismological Service detected and located 1227 and 955 earthquakes in the region under consideration, respectively. The strongest event in the analysed period was the ML 4.6 Urnerboden earthquake, which occurred in the border region of cantons Uri, Glarus and Schwyz on March 6, 2017. The event was the strongest earthquake within Switzerland since the ML 5.0 Vaz earthquake of 1991. Associated ground motions indicating intensity IV were reported in a radius up to about 50 km and locally approached intensity VI in the region close to the epicentre. Derived focal mechanisms and relative hypocentre relocations of the immediate aftershocks image a NNW–SSE striking sinistral strike-slip fault. Together with other past events in this region, the Urnerboden earthquake suggests the existence of a system of sub-parallel strike-slip faults, likely within in the uppermost crystalline basement of the eastern Aar Massif. A vigorous earthquake sequence occurred close to Château-d'Oex in the Préalpes-Romandes region in western Switzerland. With a magnitude of ML 4.3, the strongest earthquake of the sequence occurred on July 1, 2017. Focal mechanism and relative relocations of fore- and aftershocks image a NNE dipping normal fault in about 4 km depth. Two similarly oriented shallow normal-fault events occurred between subalpine Molasse and Préalpes units close to Châtel-St-Denis and St. Silvester in 2017/18. Together, these events indicate a domain of NE–SW oriented extensional to transtensional deformation along the Alpine Front between Lake Geneva in the west and the Fribourg Fault in the east. The structural complexity of the Fribourg Fault is revealed by an ML 2.9 earthquake near Tafers in 2018. The event images a NW–SE striking fault segment within the crystalline basement, which might be related to the Fribourg Fault Zone. Finally, the ML 2.8 Grenchen earthquake of 2017 provides a rare example of shallow thrust faulting along the Jura fold-and-thrust belt, indicating contraction in the northwestern Alpine foreland of Switzerland.

Seismology and Tectonic Setting of the 2002 Molise, Italy, Earthquake

2004 ◽  
Vol 20 (1_suppl) ◽  
pp. 23-37 ◽  
Author(s):  
Gianluca Valensise ◽  
Daniela Pantosti ◽  
Roberto Basili
Keyword(s):  
Southern Italy ◽  
Tectonic Setting ◽  
Historical Earthquakes ◽  
Strike Slip ◽  
Normal Faulting ◽  
Axial Part ◽  
Gargano Promontory ◽  
Populated Region ◽  
East West

Two Mw 5.7 earthquakes struck a sparsely populated region of southern Italy, on October 31 and November 1, triggering a swarm-like sequence that lasted for several days. The earthquakes were caused by pure right-lateral slip between 10 and 24 km depth over a nearly vertical, previously undetected east-west fault. This mechanism is not typical for southern Italy, where normal faulting in the uppermost 12 km of the crust seems to dominate. However, east-west strike-slip faulting is kinematically consistent with the widely documented Apennines extension. The earthquake-causative fault appears to connect the Mattinata fault, a major active strike-slip feature cutting across the Gargano promontory, with east-west structures known beneath the axial part of the Apennines. The 2002 earthquakes thus highlighted a mode of earthquake release that may explain several large yet poorly understood historical earthquakes (e.g., 1361, 1456, 1731, 1930) located between the crest of the Apennines and the Adriatic coastline.

Seismic depth imaging of normal faulting in the southern Death Valley Basin

Geophysics ◽  
1998 ◽  
Vol 63 (1) ◽  
pp. 223-230 ◽  
Author(s):  
Sergio Chávez‐Pérez ◽  
John N. Louie ◽  
Sathish K. Pullammanappallil
Keyword(s):  
Normal Fault ◽  
Velocity Model ◽  
Death Valley ◽  
Normal Faults ◽  
Normal Faulting ◽  
Lateral Velocity ◽  
Western Basin ◽  
Depth Imaging ◽  
Arrival Times ◽  
Velocity Variations

Motivated by the need to image faults to test Cenozoic extension models for the Death Valley region of the western basin and range province, an area of strong lateral velocity variations, we examine the geometry of normal faulting in southern Death Valley by seismic depth imaging. We analyze COCORP Death Valley Line 9 to attain an enhanced image of shallow fault structure to 2.5 km depth. Previous work used standard seismic processing to infer normal faults from bed truncations, displacement of horizontal reflectors, and diffractions. We obtain a detailed velocity model by nonlinear optimization of first‐ arrival times picked from shot gathers, examine the unprocessed data for fault reflections, and use a Kirchhoff prestack depth imaging procedure to handle lateral velocity variations and arbitrary dips properly. Fault‐plane reflections reveal the listric true‐depth geometry of the normal fault at the Black Mountains range front in southern Death Valley. This is consistent with the concept of low‐angle extension in this region and strengthens its association with crustal‐scale magmatic plumbing.

scholarly journals Fault plane solutions of the 1993 and 1995 Gulf of Aqaba earthquakes and their tectonic implications

1997 ◽  
Vol 40 (6) ◽  
Author(s):  
A. K. Abdel-Fattah ◽  
H. M. Hussein ◽  
E. M. Ibrahim ◽  
A. S. Abu El Atta
Keyword(s):  
Fault Plane ◽  
Strike Slip ◽  
P Wave ◽  
Gulf Of Aqaba ◽  
Main Trend ◽  
Gulf Of Suez ◽  
Normal Faulting ◽  
Aftershock Distribution ◽  
Lateral Strike Slip ◽  
Largest Aftershock

The stereographic projection of P-wave first motions for the 3 August 1993 Gulf of Aqaba earthquake, its largest aftershock (16 h 33 min), and for the 22 November 1995 earthquake were constructed using the polarity readings of regional and teleseismic stations. The focal mechanism solutions of the 3 August 1993 mainshock and its largest aftershock represent a normal faulting mechanism with some left lateral strike slip component. The nodal planes selected as the fault imply high similarity in strike and dip. They are related to a local fault striking NW-SE and dipping to the SW. The selected fault planes are in good agreement with the aftershock distribution. For the main shock of the 22 November 1995, the fault plane solution displays the same mechanism (normal faulting with left lateral strike slip component) with a plane striking N-S and dipping to the west. The fault plane is greatly conformable with the direction of the regional tectonics and also with the aftershock distribution. The main trend of the extension stress pattern is in a NE-SW direction, corresponding to the rifting direction of the Gulf of Suez and may be related to the paleostress along the Gulf of Suez and Aqaba during the Middle to Late Miocene.

Relocation of Koyna earthquakes

1980 ◽  
Vol 70 (5) ◽  
pp. 1849-1868
Author(s):  
B. K. Rastogi ◽  
P. Talwani
Keyword(s):  
Fault Plane ◽  
Seismic Velocity ◽  
Landsat Imagery ◽  
Velocity Model ◽  
Strike Slip ◽  
Normal Faulting ◽  
Large Area ◽  
Fault Plane Solutions ◽  
Lateral Strike Slip ◽  
Induced Earthquake

abstract The Koyna earthquake of December 10, 1967 was the most damaging reservoir-induced earthquake. It was followed by a long sequence of earthquakes which is still continuing. Precise locations of the Koyna earthquakes have been very much disputed as different locations of the main earthquake and stronger aftershocks were obtained by various workers. Over 1,500 epicenters of Koyna earthquakes through 1973 were obtained by Guha et al. (1974). They cover a large area in a diffused pattern. In view of the continuing seismicity and a recently obtained seismic velocity model, the larger events (ML ≧ 4.0) and about 300 selected smaller events (ML < 4.0) were relocated. The relocated epicenters show some concentration and suggest the possibility of two trends in the NNE and NW directions. There is a NNE trend of epicenters near the dam and another about 20 km west of the reservoir. The NW trend cuts through these NNE trends. The events were grouped to obtain their composite fault-plane solutions which indicate left-lateral strike-slip faulting along the NNE faults and normal faulting in the NW direction. Faults observed in the LANDSAT imagery match with these trends.

Microearthquake study of the Elsinore fault zone, Southern California

1974 ◽  
Vol 64 (1) ◽  
pp. 187-203
Author(s):  
David Langenkam ◽  
Jim Combs
Keyword(s):  
Fault Zone ◽  
Southern California ◽  
Velocity Model ◽  
High Gain ◽  
Strike Slip ◽  
San Jacinto Fault ◽  
Crustal Velocity ◽  
Crustal Velocity Model ◽  
Slip Displacement ◽  
East West

Abstract Microearthquakes along the Elsinore fault zone, southern California, were monitored during the summer and fall of 1972. Four arrays of at least five portable, high-gain, seismographs were operated for about 12 days each from the vicinity of Corona to just north of the Mexican border. Over 5,000 hr of noisefree records were accumulated and analyzed. The recorded rates of seismic activity show a marked increase going from north to south along the fault— 0.5 events per day in the vicinity of Lake Elsinore to 3.7 events per day in the south near Monument Peak. Fifty-three events located, assuming a four-layer crustal-velocity model, show considerable scatter along the fault and are generally very shallow, averaging 3.3 km below sea level. A signal duration (D) versus magnitude (M) relationship was found: M = −1.9+2.0 log D. First motions of the located earthquakes indicate a complex pattern of faulting along the Elsinore fault zone. In comparison to the San Jacinto Fault to the east, the Elsinore Fault shows very little strike-slip displacement and is a seismically quiet area except for a localized area of east-west faulting in the far south near Vallecito Mountain.

Seismotectonic Analysis of the 2019–2020 Puerto Rico Sequence: The Value of Absolute Earthquake Relocations in Improved Interpretations of Active Tectonics

2021 ◽  
Author(s):  
Copeland W. Cromwell ◽  
Kevin P. Furlong ◽  
Eric A. Bergman ◽  
Harley M. Benz ◽  
Will L. Yeck ◽  
...  
Keyword(s):  
Puerto Rico ◽  
Moment Tensor ◽  
Active Tectonics ◽  
Strike Slip ◽  
Fault System ◽  
Normal Faulting ◽  
Rupture Area ◽  
Extensional Faulting ◽  
Dextral Strike Slip ◽  
East West

Abstract We present a new catalog of calibrated earthquake relocations from the 2019–2020 Puerto Rico earthquake sequence related to the 7 January 2020 Mw 6.4 earthquake that occurred offshore of southwest Puerto Rico at a depth of 15.9 km. Utilizing these relocated earthquakes and associated moment tensor solutions, we can delineate several distinct fault systems that were activated during the sequence and show that the Mw 6.4 mainshock may have resulted from positive changes in Coulomb stress from earlier events. Seismicity and mechanisms define (1) a west–southwest (∼260°) zone of seismicity comprised of largely sinistral strike-slip and oblique-slip earthquakes that mostly occurs later in the sequence and to the west of the mainshock, (2) an area of extensional faulting that includes the mainshock and occurs largely within the mainshock’s rupture area, and (3) an north–northeast (∼30°)-striking zone of seismicity, consisting primarily of dextral strike-slip events that occurs before and following the mainshock and generally above (shallower than) the normal-faulting events. These linear features intersect within the Mw 6.4 mainshock’s fault plane in southwest Puerto Rico. In addition, we show that earthquake relocations for M 4+ normal-faulting events, when traced along their fault planes, daylight along east–west-trending bathymetric features offshore of southwest Puerto Rico. Correlation of these normal-faulting events with bathymetric features suggests an active fault system that may be a contributor to previously uncharacterized seismic hazards in southwest Puerto Rico.

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