Mainshock and Aftershock Sequence Simulation in Geometrically Complex Fault Zones

2020 ◽  
Author(s):  
So Ozawa ◽  
Ryosuke Ando
Keyword(s):  
Fault Zones ◽  
Aftershock Sequence ◽  
Complex Fault ◽  
Geometrically Complex ◽  
Sequence Simulation

A fault model for the Nahanni earthquakes from aftershock studies

1990 ◽  
Vol 80 (6A) ◽  
pp. 1553-1570 ◽  
Author(s):  
R. B. Horner ◽  
R. J. Wetmiller ◽  
M. Lamontagne ◽  
M. Plouffe
Keyword(s):  
Stress Drop ◽  
Main Shock ◽  
Fault Zones ◽  
Aftershock Sequence ◽  
Aftershock Activity ◽  
Thrust Faulting ◽  
Rupture Plane ◽  
To Come ◽  
Activity Mechanism ◽  
Secondary Fault

Abstract Relative locations of 323 large aftershocks (M 3.0 or greater) in the period from 5 October 1985 to 25 March 1988 show that the Ms 6.6 event on 5 October 1985 initiated at 62.208°N, 124.217°W, about 2.5 km northeast of the Ms 6.9 main shock on 23 December 1985. The overall aftershock distribution suggests the October rupture was primarily a west-dipping, low-angle thrust. In subsequent aftershock activity, the main rupture plane was marked by a distinct quiescent area of about 200 km2 that persisted until the 23 December event. Most of the stress drop and slip occurred in this area. Following the 23 December rupture, a similar sized quiescent zone was also observed; however, it was only evident during the first 24 hr of the aftershock sequence, and the area was about 50 per cent too small to yield the overall stress drop. The additional area appeared to come from secondary rupture zones that developed coincident with the main shock rupture. Precise locations of 182 small (M 3.0 or less) aftershocks recorded during a third field survey from 12 to 21 September 1986 indicated at least one and probably three high-angle faults. Composite mechanism solutions showed thrust faulting except in a region directly south of the main shock rupture areas where there is a bend in one of the secondary fault zones and a concentration of aftershock activity. Mechanism solutions calculated for five of the largest aftershocks in the same region also indicated a similar variability. Development of secondary fault zones explained the increased complexity of the December event and may also provide an explanation for the vertical peak acceleration exceeding 2 g that was recorded about 10 sec after the December rupture initiated.

scholarly journals PSHA after a strong earthquake: hints for the recovery

2016 ◽  
Vol 59 ◽  
Author(s):  
L. Peruzza ◽  
R. Gee ◽  
B. Pace ◽  
G. Roberts ◽  
O. Scotti ◽  
...  
Keyword(s):  
Hazard Analysis ◽  
Central Italy ◽  
Safety Evaluation ◽  
Preliminary Evidence ◽  
Source Model ◽  
Aftershock Sequence ◽  
Earthquake Occurrence ◽  
Central Italy Earthquake ◽  
Complex Fault ◽  
Fault Source

<p>We perform aftershock probabilistic seismic hazard analysis (APSHA) of the ongoing aftershock sequence following the Amatrice August 24th, 2016 Central Italy earthquake. APSHA is a time-dependent PSHA calculation where earthquake occurrence rates decrease after the occurrence of a mainshock following an Omori-type decay. In this paper we propose a fault source model based on preliminary evidence of the complex fault geometry associated with the mainshock. We then explore the possibility that the aftershock seismicity is distributed either uniformly or non-uniformly across the fault source. The hazard results are then computed for short-intermediate exposure periods (1-3 months, 1 year). They are compared to the background hazard and intended to be useful for post-earthquake safety evaluation.</p>

scholarly journals Injection‐Induced Earthquakes on Complex Fault Zones of the Raton Basin Illuminated by Machine‐Learning Phase Picker and Dense Nodal Array

2020 ◽  
Vol 47 (14) ◽  
Author(s):  
Ruijia Wang ◽  
Brandon Schmandt ◽  
Miao Zhang ◽  
Margaret Glasgow ◽  
Eric Kiser ◽  
...  
Keyword(s):  
Machine Learning ◽  
Fault Zones ◽  
Learning Phase ◽  
Induced Earthquakes ◽  
Complex Fault

scholarly journals Injection-induced earthquakes on complex fault zones of the Raton Basin illuminated by machine-learning phase picker and dense nodal array

2020 ◽  
Author(s):  
Ruijia Wang ◽  
Brandon Schmandt ◽  
Miao Zhang ◽  
Margaret Elizabeth Glasgow ◽  
Eric Kiser ◽  
...  
Keyword(s):  
Machine Learning ◽  
Fault Zones ◽  
Learning Phase ◽  
Induced Earthquakes ◽  
Complex Fault

Aftershock Sequence and Statistics of the 2017 Mw 5.5 Pohang, South Korea, Earthquake: Implications of Fault Heterogeneity and Postseismic Relaxation

2020 ◽  
Vol 110 (5) ◽  
pp. 2031-2046
Author(s):  
Jeong-Ung Woo ◽  
Minook Kim ◽  
Junkee Rhie ◽  
Tae-Seob Kang
Keyword(s):  
Spatial Distribution ◽  
Stress Field ◽  
South Korea ◽  
Aftershock Sequence ◽  
Fault System ◽  
Postseismic Deformation ◽  
Earthquake Catalog ◽  
B Values ◽  
Complex Fault ◽  
Anisotropic Expansion

ABSTRACT The sequence of foreshocks, mainshock, and aftershocks associated with a fault rupture is the result of interactions of complex fault systems, the tectonic stress field, and fluid movement. Analysis of shock sequences can aid our understanding of the spatial distribution and magnitude of these factors, as well as provide seismic hazard assessment. The 2017 Mw 5.5 Pohang earthquake sequence occurred following fluid-induced seismic activity at a nearby enhanced geothermal system site and is an example of reactivation of a critically stressed fault system in the Pohang basin, South Korea. We created an earthquake catalog based on unsupervised data mining and measuring the energy ratio between short- and long-window seismograms recorded by a temporary seismic network. The spatial distribution of approximately 4000 relocated aftershocks revealed four fault segments striking southwestward. We also determined that the three largest earthquakes (ML&gt;4) were located at the boundary of two fault segments. We infer that locally concentrated stress at the junctions of the faults caused such large earthquakes and that their ruptures on multiple segments can explain the high proportion of non-double-couple components. The area affected by aftershocks continues to expand to the southwest and northeast by 0.5 and 1  km decade−1, respectively, which may result from postseismic deformation or sequentially transferred static coulomb stress. The b-values of the Gutenberg–Richter relationship temporarily increased for the first three days of the aftershock sequence, suggesting that the stress field was perturbed. The b-values were generally low (&lt;1) and locally variable throughout the aftershock area, which may be due to the complex fault structures and material properties. Furthermore, the mapped p-values of the Omori law vary along strike, which may indicate anisotropic expansion speeds in the aftershock region.

Drawing faults

2019 ◽  
pp. 42-56
Author(s):  
Matthew J. Genge
Keyword(s):  
Worked Examples ◽  
Fault Zones ◽  
Complex Fault ◽  
Key Features ◽  
Made In

Faults are commonly encountered during geology fieldwork and are frequently the subjects of sketches in the field. This chapter introduces simple field sketches using faults as an example. It considers how best to draw faults in the field and the important features of these structures to record. Two worked examples of field sketches are given and focus on the techniques employed to draw their geometries accurately. The rules introduced in Chapter 2 are revisited, as are the techniques of blocking-in, adding key features, and the importance of labels and scale. Both simple faults and complex fault zones are considered in the chapter. Common mistakes made in geological sketches are also described.

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