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 <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.

Evidence of Previous Faulting along the 2019 Ridgecrest, California, Earthquake Ruptures

2020 ◽  
Vol 110 (4) ◽  
pp. 1427-1456 ◽  
Author(s):  
Jessica Ann Thompson Jobe ◽  
Belle Philibosian ◽  
Colin Chupik ◽  
Timothy Dawson ◽  
Scott E. K. Bennett ◽  
...  
Keyword(s):  
Active Fault ◽  
Active Faults ◽  
Ground Surface ◽  
Vertical Motion ◽  
Fault System ◽  
Field Observations ◽  
Surface Rupture ◽  
Earthquake Ruptures ◽  
Slip Displacement ◽  
Surface Ruptures

ABSTRACT The July 2019 Ridgecrest earthquakes in southeastern California were characterized as surprising by some, because only ∼35% of the rupture occurred on previously mapped faults. Employing more detailed inspection of pre-event high-resolution topography and imagery in combination with field observations, we document evidence of active faulting in the landscape along the entire fault system. Scarps, deflected drainages, and lineaments and contrasts in topography, vegetation, and ground color demonstrate previous slip on a dense network of orthogonal faults, consistent with patterns of ground surface rupture observed in 2019. Not all of these newly mapped fault strands ruptured in 2019. Outcrop-scale field observations additionally reveal tufa lineaments and sheared Quaternary deposits. Neotectonic features are commonly short (<2  km), discontinuous, and display en echelon patterns along both the M 6.4 and M 7.1 ruptures. These features are generally more prominent and better preserved outside the late Pleistocene lake basins. Fault expression may also be related to deformation style: scarps and topographic lineaments are more prevalent in areas where substantial vertical motion occurred in 2019. Where strike-slip displacement dominated in 2019, the faults are mainly expressed by less prominent tonal and vegetation features. Both the northeast- and northwest-trending active-fault systems are subparallel to regional bedrock fabrics that were established as early as ∼150  Ma, and may be reactivating these older structures. Overall, we estimate that 50%–70% (i.e., an additional 15%–35%) of the 2019 surface ruptures could have been recognized as active faults with detailed inspection of pre-earthquake data. Similar detailed mapping of potential neotectonic features could help improve seismic hazard analyses in other regions of eastern California and elsewhere that likely have distributed faulting or incompletely mapped faults. In areas where faults cannot be resolved as single throughgoing structures, we recommend a zone of potential faulting should be used as a hazard model input.

Do active faults’ clay mineral compositions affect whether earthquake ruptures they host will displace the surface?

2021 ◽  
Author(s):  
Selina S. Fenske ◽  
Virginia G. Toy ◽  
Bernhard Schuck ◽  
Anja M. Schleicher ◽  
Klaus Reicherter
Keyword(s):  
Fault Zone ◽  
Clay Mineral ◽  
Active Faults ◽  
Surface Displacement ◽  
Surface Rupture ◽  
Near Surface ◽  
Ground Shaking ◽  
Physical Measurements ◽  
Surface Displacements ◽  
Earthquake Ruptures

<p>The tectonophysical paradigm that earthquake ruptures should not start, or easily propagate into, the shallowest few kilometers of Earth’s crust makes it difficult to understand why damaging surface displacements have occurred during historic events. The paradigm is supported by decades of analyses demonstrating that near the surface, most major fault zones are composed of clay minerals – particularly extraordinarily weak smectites – which most laboratory physical measurements suggest should prevent surface rupture if present. Recent studies of New Zealand’s Alpine Fault Zone (AFZ) demonstrate smectites are absent from some near surface fault outcrops, which may explain why this fault was able to offset the surface locally in past events. The absence of smectites in places within the AFZ can be attributed to locally exceptionally high geothermal gradients related to circulation of meteoric (surface-derived) water into the fault zone, driven by significant topographic gradients. The record of surface rupture of the AFZ is heterogeneous, and no one has yet systematically examined the distribution of segments devoid of evidence for recent displacement. There are significant implications for seismic hazard, which comprises both surface displacements and ground shaking with intensity related to the area of fault plane that ruptures (which will be reduced if ruptures do not reach the surface).  We will present results of new rigorous XRD clay mineral analyses of AFZ principal slip zone gouges that indicate where smectites are present, and consider if these display systematic relationships to surface displacement records. We also plan to apply the same methodology to the Carboneras Fault Zone in Spain, and the infrequent Holocene-active faults in Western Germany.</p>

scholarly journals The San Andreas Fault Paleoseismic Record at Elizabeth Lake: Why are There Fewer Surface-Rupturing Earthquakes on the Mojave Section?

2021 ◽  
Author(s):  
Sean P. Bemis ◽  
Kate Scharer ◽  
James F. Dolan
Keyword(s):  
San Andreas Fault ◽  
Active Faults ◽  
Structural Complexity ◽  
Plate Motion ◽  
Fault System ◽  
San Andreas ◽  
Time Period ◽  
Earthquake Ruptures ◽  
Major Fault ◽  
Restraining Bend

ABSTRACT The structural complexity of active faults and the stress release history along the fault system may exert control on the locus and extent of individual earthquake ruptures. Fault bends, in particular, are often invoked as a possible mechanism for terminating earthquake ruptures. However, there are few records available to examine how these factors may influence the along-fault recurrence of earthquakes. We present a new paleoearthquake chronology for the southern San Andreas fault at Elizabeth Lake and integrate this record with existing paleoearthquake records to examine how the timing and frequency of earthquakes vary through a major restraining bend. This restraining bend features a mature, throughgoing right-lateral strike-slip fault, two major fault intersections, proposed subsurface fault dip changes, and a >200  km long section of fault misaligned with the regional plate motion. The Frazier Mountain, Elizabeth Lake, Pallett Creek, Wrightwood, and Pitman Canyon paleoseismic sites are located on this relatively linear surface trace of the San Andreas fault between fault bends. Our paleoseismic investigations at Elizabeth Lake document 4–5 earthquakes, since ∼1100  C.E., similar to the number of earthquakes recorded at Pallett Creek. In contrast, the Frazier Mountain and Wrightwood sites each record 8–9 earthquakes during this same time period. Differences in earthquake frequency demonstrate that fewer earthquakes rupture the central portion of the restraining bend than occur near the fault bends and intersections. Furthermore, the similarity of earthquake records from the Bidart Fan paleoseismic site northwest of the restraining bend and the Frazier Mountain paleoseismic site suggests that the broad, 30° curve of the Big Bend section of the San Andreas fault exerts less influence on fault rupture behavior than the 3D geometry of the Mojave sections of the fault.

scholarly journals Revision of the geological context of the Port-au-Prince, Haiti, metropolitan area: implications for seismic microzonation

2014 ◽  
Vol 2 (2) ◽  
pp. 1613-1635
Author(s):  
M. Terrier ◽  
A. Bialkowski ◽  
A. Nachbaur ◽  
C. Prépetit ◽  
Y. F. Joseph
Keyword(s):  
Metropolitan Area ◽  
Seismic Risk ◽  
Morphological Analysis ◽  
Active Faults ◽  
Seismic Microzonation ◽  
Ground Movement ◽  
Fault System ◽  
Surface Rupture ◽  
Development Policies ◽  
The Impact

Abstract. A geological study has been conducted in the framework of the microzonation of Portau- Prince, Haiti. It reveals the deposit of Miocene and Pliocene formations in a marine environment and the impact on these deposits of the Enriquillo-Plantain Garden N80° E fault system and of N110° E faults. The tectonic and morphological analysis indicates motion during the Quaternary along several mapped reverse left-lateral N110° E faults affecting the capital. Assessing ground-movement hazards represents an integral component of seismic microzonation. The geological results have provided essential groundwork for this assessment. Seismic microzonation aims to take seismic risk more fully into account in the city's urbanization and development policies. To this end, assumptions are made as to risks induced by surface rupture and ground movement from active faults.

scholarly journals Active Faults sources of the Morelia-Acambay Fault System, Mexico based on Paleoseismology and the estimation of magnitude <i>M<sub>w</sub></i> from fault dimensions

2018 ◽  
Author(s):  
Avith Mendoza-Ponce ◽  
Angel Figueroa-Soto ◽  
Diana Soria-Caballero ◽  
Víctor Hugo Garduño-Monroy
Keyword(s):  
Subduction Zone ◽  
Deformation Zone ◽  
Active Faults ◽  
Volcanic Belt ◽  
Fault System ◽  
Seismic Sequence ◽  
Surface Rupture ◽  
Slip Rates ◽  
Mexican Volcanic Belt ◽  
Oblique Convergence

Abstract. The Morelia-Acambay fault System (MAFS), located in the central part of the Trans-Mexican Volcanic Belt (TMVB) is delimited by an active transtensive deformation zone associated with the oblique subduction zone between the Cocos and North American plates, with a convergence velocity of 55 mm/yr at the latitude of the state of Michoacán, México. Part of the oblique convergence is transferred to the central TMVB, just in the MAFS zone, where the slip rates range from 0.009 to 2.78 mm/year. The occurrence of great earthquakes like the Acambay earthquake (Ms = 6.7) on November 19, 1912 with a surface rupture, and in Maravatío, 1979 with Mb = 5.3 are located into the MAFS. The zone is seismically active but with large periods of recurrence, as revealed by the seismic sequence (2.5 

scholarly journals Surface-Rupturing Historical Earthquakes in Australia and Their Environmental Effects: New Insights from Re-Analyses of Observational Data

Geosciences ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 408 ◽  
Author(s):  
King ◽  
Quigley ◽  
Clark
Keyword(s):  
Observational Data ◽  
Environmental Effects ◽  
Active Faults ◽  
Magnetic Data ◽  
Future Research ◽  
Surface Rupture ◽  
Secondary Fracture ◽  
Geological Evidence ◽  
Surface Ruptures ◽  
Strong Control

We digitize surface rupture maps and compile observational data from 67 publications on ten of eleven historical, surface-rupturing earthquakes in Australia in order to analyze the prevailing characteristics of surface ruptures and other environmental effects in this crystalline basement-dominated intraplate environment. The studied earthquakes occurred between 1968 and 2018, and range in moment magnitude (Mw) from 4.7 to 6.6. All earthquakes involved co-seismic reverse faulting (with varying amounts of strike-slip) on single or multiple (1–6) discrete faults of ≥ 1 km length that are distinguished by orientation and kinematic criteria. Nine of ten earthquakes have surface-rupturing fault orientations that align with prevailing linear anomalies in geophysical (gravity and magnetic) data and bedrock structure (foliations and/or quartz veins and/or intrusive boundaries and/or pre-existing faults), indicating strong control of inherited crustal structure on contemporary faulting. Rupture kinematics are consistent with horizontal shortening driven by regional trajectories of horizontal compressive stress. The lack of precision in seismological data prohibits the assessment of whether surface ruptures project to hypocentral locations via contiguous, planar principal slip zones or whether rupture segmentation occurs between seismogenic depths and the surface. Rupture centroids of 1–4 km in depth indicate predominantly shallow seismic moment release. No studied earthquakes have unambiguous geological evidence for preceding surface-rupturing earthquakes on the same faults and five earthquakes contain evidence of absence of preceding ruptures since the late Pleistocene, collectively highlighting the challenge of using mapped active faults to predict future seismic hazards. Estimated maximum fault slip rates are 0.2–9.1 m Myr-1 with at least one order of uncertainty. New estimates for rupture length, fault dip, and coseismic net slip can be used to improve future iterations of earthquake magnitude—source size—displacement scaling equations. Observed environmental effects include primary surface rupture, secondary fracture/cracks, fissures, rock falls, ground-water anomalies, vegetation damage, sand-blows / liquefaction, displaced rock fragments, and holes from collapsible soil failure, at maximum estimated epicentral distances ranging from 0 to ~250 km. ESI-07 intensity-scale estimates range by ± 3 classes in each earthquake, depending on the effect considered. Comparing Mw-ESI relationships across geologically diverse environments is a fruitful avenue for future research.

Bathymetry and uplift rate of the Gulf of Aqaba, Dead Sea Fault.

2021 ◽  
Author(s):  
Matthieu Ribot ◽  
Yann Klinger ◽  
Edwige Pons-Branchu ◽  
Marthe Lefevre ◽  
Sigurjón Jónsson
Keyword(s):  
High Resolution ◽  
Tectonic Evolution ◽  
Active Faults ◽  
Major Change ◽  
Dead Sea ◽  
Fault System ◽  
Arabian Plate ◽  
Gulf Of Aqaba ◽  
Uplift Rate ◽  
The Dead

&lt;p&gt;Initially described in the late 50&amp;#8217;s, the Dead Sea Fault system connects at its southern end to the Red Sea extensive system, through a succession of left-stepping faults. In this region, the left-lateral differential displacement of the Arabian plate with respect to the Sinai micro-plate along the Dead Sea fault results in the formation of a depression corresponding to the Gulf Aqaba. We acquired new bathymetric data in the areas of the Gulf of Aqaba and Strait of Tiran during two marine campaigns (June 2018, September 2019) in order to investigate the location of the active faults, which structure and control the morphology of the area. The high-resolution datasets (10-m posting) allow us to present a new fault map of the gulf and to discuss the seismic potential of the main active faults.&lt;/p&gt;&lt;p&gt;We also investigated the eastern margin of the Gulf of Aqaba and Tiran island to assess the vertical uplift rate. To do so, we computed high-resolution topographic data and we processed new series of U-Th analyses on corals from the uplifted marine terraces.&lt;/p&gt;&lt;p&gt;Combining our results with previous studies, we determined the local and the regional uplift in the area of the Gulf of Aqaba and Strait of Tiran.&lt;/p&gt;&lt;p&gt;Eventually, we discussed the tectonic evolution of the gulf since the last major change of the tectonic regime and we propose a revised tectonic evolution model of the area.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals Assembly of a large earthquake from a complex fault system: Surface rupture kinematics of the 4 April 2010 El Mayor–Cucapah (Mexico) Mw 7.2 earthquake

Geosphere ◽  
2014 ◽  
Vol 10 (4) ◽  
pp. 797-827 ◽  
Author(s):  
John M. Fletcher ◽  
Orlando J. Teran ◽  
Thomas K. Rockwell ◽  
Michael E. Oskin ◽  
Kenneth W. Hudnut ◽  
...  
Keyword(s):  
Large Earthquake ◽  
Fault System ◽  
Surface Rupture ◽  
Complex Fault ◽  
Rupture Kinematics ◽  
Complex Fault System

scholarly journals Exploring the shallow structure of the San Ramón thrust fault in Santiago, Chile (~33.5° S), using active seismic and electric methods

Solid Earth ◽  
2014 ◽  
Vol 5 (2) ◽  
pp. 837-849 ◽  
Author(s):  
D. Díaz ◽  
A. Maksymowicz ◽  
G. Vargas ◽  
E. Vera ◽  
E. Contreras-Reyes ◽  
...  
Keyword(s):  
Seismic Anisotropy ◽  
Average Length ◽  
Sedimentary Cover ◽  
Hanging Wall ◽  
Thrust Fault ◽  
Fault System ◽  
Surface Rupture ◽  
Thrust Tectonics ◽  
Rock Substratum ◽  
Fault Scarps

Abstract. The crustal-scale west-vergent San Ramón thrust fault system, which lies at the foot of the main Andean Cordillera in central Chile, is a geologically active structure with manifestations of late Quaternary complex surface rupture on fault segments along the eastern border of the city of Santiago. From the comparison of geophysical and geological observations, we assessed the subsurface structural pattern that affects the sedimentary cover and rock-substratum topography across fault scarps, which is critical for evaluating structural models and associated seismic hazard along the related faults. We performed seismic profiles with an average length of 250 m, using an array of 24 geophones (Geode), with 25 shots per profile, to produce high-resolution seismic tomography to aid in interpreting impedance changes associated with the deformed sedimentary cover. The recorded travel-time refractions and reflections were jointly inverted by using a 2-D tomographic approach, which resulted in variations across the scarp axis in both the velocities and the reflections that are interpreted as the sedimentary cover-rock substratum topography. Seismic anisotropy observed from tomographic profiles is consistent with sediment deformation triggered by west-vergent thrust tectonics along the fault. Electrical soundings crossing two fault scarps were used to construct subsurface resistivity tomographic profiles, which reveal systematic differences between lower resistivity values in the hanging wall with respect to the footwall of the geological structure, and clearly show well-defined east-dipping resistivity boundaries. These boundaries can be interpreted in terms of structurally driven fluid content change between the hanging wall and the footwall of the San Ramón fault. The overall results are consistent with a west-vergent thrust structure dipping ~55° E in the subsurface beneath the piedmont sediments, with local complexities likely associated with variations in fault surface rupture propagation, fault splays and fault segment transfer zones.

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