Seismic doublets and a complex seismic sequence controlled by the rotation of the Juan Fernández microplate

2021 ◽  
Author(s):  
Simone Cesca ◽  
Carla Valenzuela Malebrán ◽  
José Ángel López-Comino ◽  
Timothy Davis ◽  
Carlos Tassara ◽  
...  
Keyword(s):  
Source Parameters ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Joint Analysis ◽  
Seismic Sequence ◽  
Local Data ◽  
Study Region ◽  
Coulomb Stress Changes ◽  
Earthquake Source Parameters ◽  
Stress Changes

<p> A complex seismic sequence took place in 2014 at the Juan Fernández microplate, a small microplate located between Pacific, Nazca and Antarctica plates. Despite the remoteness of the study region and the lack of local data, we were able to resolve earthquake source parameters and to reconstruct the complex seismic sequence, by using modern waveform-based seismological techniques. The sequence started with an exceptional Mw 7.1-6.7 thrust – strike slip earthquake doublet, the first subevent being the largest earthquake ever recorded in the region and one of the few rare thrust earthquakes in a region otherwise characterized by normal faulting and strike slip earthquakes. The joint analysis of seismicity and focal mechanisms suggest the activation of E-W and NE-SW faults or of an internal curved pseudofault, which is formed in response to the microplate rotation, with alternation of thrust and strike-slip earthquakes. Seismicity migrated Northward in its final phase, towards the microplate edge, where a second doublet with uneven focal mechanisms occurred. The sequence rupture kinematics is well explained by Coulomb stress changes imparted by the first subevent. Our analysis show that compressional stresses, which have been mapped at the northern boundary of the microplate, but never accompanied by large thrust earthquakes, can be accommodated by the rare occurrence of large, impulsive, shallow thrust earthquakes, with a considerable tsunamigenic potential.</p>

scholarly journals ANALYSING POST-SEISMIC DEFORMATION OF IZMIT EARTHQUAKE WITH INSAR, GNSS AND COULOMB STRESS MODELLING

2016 ◽  
Vol XLI-B1 ◽  
pp. 417-421 ◽  
Author(s):  
R. Alac Barut ◽  
J. Trinder ◽  
C. Rizos
Keyword(s):  
Measurement Techniques ◽  
Satellite System ◽  
Northern Region ◽  
Strike Slip ◽  
Coulomb Stress ◽  
North West ◽  
Coulomb Stress Changes ◽  
Izmit Earthquake ◽  
The North ◽  
Stress Changes

On August 17<sup>th</sup> 1999, a M<sub>w</sub> 7.4 earthquake struck the city of Izmit in the north-west of Turkey. This event was one of the most devastating earthquakes of the twentieth century. The epicentre of the Izmit earthquake was on the North Anatolian Fault (NAF) which is one of the most active right-lateral strike-slip faults on earth. However, this earthquake offers an opportunity to study how strain is accommodated in an inter-segment region of a large strike slip fault. In order to determine the Izmit earthquake post-seismic effects, the authors modelled Coulomb stress changes of the aftershocks, as well as using the deformation measurement techniques of Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS). The authors have shown that InSAR and GNSS observations over a time period of three months after the earthquake combined with Coulomb Stress Change Modelling can explain the fault zone expansion, as well as the deformation of the northern region of the NAF. It was also found that there is a strong agreement between the InSAR and GNSS results for the post-seismic phases of investigation, with differences less than 2mm, and the standard deviation of the differences is less than 1mm.

scholarly journals Parageneses of fractures in large fault zones of West Transbaikalia

2018 ◽  
Vol 9 (3) ◽  
pp. 889-908
Author(s):  
A. V. Cheremnykh
Keyword(s):  
Quantitative Analysis ◽  
Fault Zones ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Rock Fracturing ◽  
Study Region ◽  
Tectonic Development ◽  
Paleoseismic Dislocations ◽  
The Right ◽  
Cenozoic Sediments

Our study was focused on the parageneses of heterogeneous fractures in the large fault zones of West Transbaikalia,Russia. We reconstructed the latest deformation in the fault zones of Transbaikalia, within which paleoseismic dislocations are known and M 4.7 earthquakes take place. To obtain statistically justified solutions on the kinematic types of the largest faults ofWest Transbaikalia, we collected the required data and conducted the structural and paragenetic analysis of the fractures in the study area. In the Chikoi-Ingoda, Khilok, North Tugnui andNorth Zaganfault zones, we created a network of 54 observation points and measured more than 5500 details of local fractures and faults. Recorded were the observed slickensides, the displacements of markers, and other details of rock fracturing. Based on the analysis results, we calculated a ratio of heterochronous dynamic settings for formation of the observed fault group. It shows that NW-SE-trending extension and compression are dominant in the study region. The parageneses of E-NE-striking faults, i.e. regional faults longitudinal to the depressions ofWest Transbaikalia, are abundant in the studied fault zones and generally observed in heterochronous formations, including the Cenozoic sediments. This fact, along with the focal mechanisms of the recently recorded earthquakes, suggests that these faults are young. Besides, in the Tugnui basin and the area southeast of the Chikoy depression, the right-lateral strike-slip setting was reconstructed for E-NE-trending faults. Our study pioneers in the quantitative analysis of the fault parageneses ofWest Transbaikalia. Considering the development of the network of large faults in the study area, we reconstructed the main stages and the kinematic types of the second-order fractures that constitute the internal structure of the studied fault zones at each stage of their tectonic development. 

scholarly journals ANALYSING POST-SEISMIC DEFORMATION OF IZMIT EARTHQUAKE WITH INSAR, GNSS AND COULOMB STRESS MODELLING

2016 ◽  
Vol XLI-B1 ◽  
pp. 417-421
Author(s):  
R. Alac Barut ◽  
J. Trinder ◽  
C. Rizos
Keyword(s):  
Measurement Techniques ◽  
Satellite System ◽  
Northern Region ◽  
Strike Slip ◽  
Coulomb Stress ◽  
North West ◽  
Coulomb Stress Changes ◽  
Izmit Earthquake ◽  
The North ◽  
Stress Changes

On August 17<sup>th</sup> 1999, a M<sub>w</sub> 7.4 earthquake struck the city of Izmit in the north-west of Turkey. This event was one of the most devastating earthquakes of the twentieth century. The epicentre of the Izmit earthquake was on the North Anatolian Fault (NAF) which is one of the most active right-lateral strike-slip faults on earth. However, this earthquake offers an opportunity to study how strain is accommodated in an inter-segment region of a large strike slip fault. In order to determine the Izmit earthquake post-seismic effects, the authors modelled Coulomb stress changes of the aftershocks, as well as using the deformation measurement techniques of Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS). The authors have shown that InSAR and GNSS observations over a time period of three months after the earthquake combined with Coulomb Stress Change Modelling can explain the fault zone expansion, as well as the deformation of the northern region of the NAF. It was also found that there is a strong agreement between the InSAR and GNSS results for the post-seismic phases of investigation, with differences less than 2mm, and the standard deviation of the differences is less than 1mm.

scholarly journals Application for source parameters calculations as input for static stress changes studies

2007 ◽  
Vol 40 (4) ◽  
pp. 2008
Author(s):  
P. M. Paradisopoulou ◽  
E. E. Papadimitriou ◽  
V. G. Karakostas ◽  
A. Kilias
Keyword(s):  
Scaling Laws ◽  
Source Parameters ◽  
Active Faults ◽  
Static Stress ◽  
Coulomb Stress ◽  
Coseismic Slip ◽  
Earthquake Source Parameters ◽  
Fault Parameters ◽  
Stress Changes ◽  
Stress Application

The study of static Coulomb Stress changes requires initially the collection of information on the major active faults in a study area concerning their geometry and kinematic properties and then a series of complex calculation for stress changes that are associated with both coseismic displacements of the stronger events and the tectonic loading on these major faults. The Coulomb Stress Application has been developed as a tool to provide a user-friendly way of entering the necessary data and an efficient way to perform the complex calculations procedure. More specifically the aim of the application is a) the collection of data (catalogues of earthquakes, fault parameters) in a relational database, b) the calculation of earthquake source parameters such as the length and the width of the causative fault, and the coseismic slip by using available scaling laws, and finally, c) the execution of all the necessary programs and scripts (e.g. dis3dop.exe, GMT package) to get a map of static stress changes for an area. Coulomb Stress application provides a way to store these data for a study area and it is a method to perform a series of calculations by plotting a series of maps and examine the results for a number of cases.

Earthquake Source Parameters in Southwestern China and Their Rheological Implications

2020 ◽  
Vol 91 (2A) ◽  
pp. 936-947
Author(s):  
Qingdong Wang ◽  
Risheng Chu
Keyword(s):  
Southern California ◽  
Depth Distribution ◽  
Source Parameters ◽  
Focal Mechanisms ◽  
Yunnan Region ◽  
Brittle Ductile Transition ◽  
Earthquake Source Parameters ◽  
China Earthquake ◽  
International Seismological Centre ◽  
Minimum Moment

Abstract Earthquake depth distribution provides key information on rheological behavior of the crust, which usually shows a brittle–ductile transition at a depth of about 10 km. In this study, we use the generalized cut-and-paste method to obtain source parameters of 571 earthquakes in the Sichuan–Yunnan region of China between 2009 and 2017. We were able to successfully determine focal mechanisms, moment magnitudes, and centroid depths of 536 earthquakes with a minimum moment magnitude of 3.2. Our moment magnitudes and centroid depths are systematically smaller than the magnitudes (Ms and mb) and hypocenter depths from the China Earthquake Network Center and International Seismological Centre catalogs for M≥4.0 earthquakes. The earthquake depths in the Sichuan–Yunnan region are mostly in a 5–9 km range, with an average at 7.6 km. About 23% earthquakes have centroid depths &lt;5  km and are concentrated in the southern Sichuan basin. Only very few earthquakes are deeper than 19 km. Compared with the earthquake depth distribution in southern California, the Sichuan–Yunnan region has many shallower earthquakes. The depth distribution suggests that the brittle–ductile transition in the Sichuan–Yunnan region is shallower than the transition beneath southern California, which is probably due to the existence of newborn faults in the Sichuan–Yunnan region.

Finite Slip Models of the 2019 Ridgecrest Earthquake Sequence Constrained by Space Geodetic Data and Aftershock Locations

2020 ◽  
Vol 110 (4) ◽  
pp. 1660-1679 ◽  
Author(s):  
Zeyu Jin ◽  
Yuri Fialko
Keyword(s):  
Stress Transfer ◽  
Nucleation Site ◽  
Strike Slip ◽  
Earthquake Sequence ◽  
Slip Distribution ◽  
Depth Interval ◽  
Coseismic Slip ◽  
Moderate Amount ◽  
Coulomb Stress Changes ◽  
Stress Changes

ABSTRACT The July 2019 Ridgecrest, California, earthquake sequence involved two large events—the M 6.4 foreshock and the M 7.1 mainshock that ruptured a system of intersecting strike-slip faults. We present analysis of space geodetic observations including Synthetic Aperture Radar and Global Navigation Satellite System data, geological field mapping, and seismicity to constrain the subsurface rupture geometry and slip distribution. The data render a complex pattern of faulting with a number of subparallel as well as cross-cutting fault strands that exhibit variations in both strike and dip angles, including a “flower structure” formed by shallow splay faults. Slip inversions are performed using both homogeneous and layered elastic half-space models informed by the local seismic tomography data. The inferred slip distribution suggests a moderate amount of the shallow coseismic slip deficit. The peak moment release occurred in the depth interval of 3–4 km, consistent with results from previous studies of major strike-slip earthquakes, and the depth distribution of seismicity in California. We use the derived slip models to investigate stress transfer and possible triggering relationships between the M 7.1 mainshock and the M 6.4 foreshock, as well as other moderate events that occurred in the vicinity of the M 7.1 hypocenter. Triggering is discouraged for the average strike of the M 7.1 rupture (320°) but encouraged for the initial orientation of the mainshock rupture suggested by the first-motion data (340°). This lends support to a scenario according to which the earthquake rupture nucleated on a small fault that was more optimally oriented with respect to the regional stress and subsequently propagated along the less-favorably oriented pre-existing faults, possibly facilitated by dynamic weakening. The nucleation site of the mainshock experienced positive dynamic Coulomb stress changes that are much larger than the static stress changes, yet the former failed to initiate rupture.

Earthquake source parameters at the sumatran fault zone: Identification of the activated fault plane

2010 ◽  
Vol 2 (4) ◽  
Author(s):  
Madlazim Kasmolan ◽  
Bagus Santosa ◽  
Jonathan Lees ◽  
Widya Utama
Keyword(s):  
Fault Zone ◽  
Moment Tensor ◽  
Source Parameters ◽  
Earthquake Source ◽  
Joint Analysis ◽  
Seismic Fault ◽  
Earthquake Source Parameters ◽  
Sumatran Fault ◽  
Centroid Position

AbstractFifteen earthquakes (Mw 4.1–6.4) occurring at ten major segments of the Sumatran Fault Zone (SFZ) were analyzed to identify their respective fault planes. The events were relocated in order to assess hypocenter uncertainty. Earthquake source parameters were determined from three-component local waveforms recorded by IRIS-DMC and GEOFON broadband lA networks. Epicentral distances of all stations were less than 10°. Moment tensor solutions of the events were calculated, along with simultaneous determination of centroid position. Joint analysis of hypocenter position, centroid position, and nodal planes produced clear outlines of the Sumatran fault planes. The preferable seismotectonic interpretation is that the events activated the SFZ at a depth of approximately 14–210 km, corresponding to the interplate Sumatran fault boundary. The identification of this seismic fault zone is significant to the investigation of seismic hazards in the region.

Preliminary Report on the 18 May 2020 Ms 5.0 Qiaojia Earthquake, Yunnan, China

2021 ◽  
Author(s):  
Zhen Fu ◽  
Changsheng Jiang ◽  
Fengling Yin ◽  
Lei Zhang ◽  
Xuanye Shen ◽  
...  
Keyword(s):  
Stress Field ◽  
Focal Mechanism ◽  
Negative Impact ◽  
Earthquake Hazard ◽  
Focal Mechanisms ◽  
Seismogenic Fault ◽  
Coulomb Stress Changes ◽  
Ludian Earthquake ◽  
Moderate Earthquake ◽  
Stress Changes

Abstract The 18 May 2020 Ms 5.0 Qiaojia earthquake occurred in Qiaojia County, Yunnan Province, ∼25  km away from the 3 August 2014 Ms 6.5 Ludian earthquake. This earthquake was well recorded by dense local seismic stations of the Qiaojia array constructed near the Xiaojiang fault zone. The focal mechanism of the mainshock exhibited strike-slip motion with a centroid depth of 8 km. We determined the seismogenic fault of the Qiaojia earthquake using aftershock relocation with local dense seismic arrays. The mainshock is located on a previously unmapped fault. Aftershocks clearly delineated east–west rupture plane, which was not revealed by the regional seismic network due to relatively sparse stations. The length and width of the aftershock zone are ∼5  km and 3 km, respectively. The focal mechanisms of 70 aftershocks with magnitudes ML≥1.0 showed similar focal mechanism with the mainshock. The stress field inverted from focal mechanisms of the aftershocks is consistent with the tectonic stress field. The coseismic and postseismic static coulomb stress changes show that the Ludian earthquake has a negative impact on the Qiaojia earthquake with a value of −0.01  MPa, implying that the Qiaojia earthquake was unlikely statically triggered by the Ludian earthquake. The Qiaojia earthquake sequence was characterized by low b-value and low-decay rate in the aftershock area, indicating high-seismic risk in this region. The dense seismic observation allows us to study the moderate earthquake in detail and provides us with valuable information of near-fault seismicity to analyze earthquake hazard and the potential of large earthquakes in the future.

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