The 2019 Ms 4.2 and 5.2 Beiliu Earthquake Sequence in South China: Complex Conjugate Strike-Slip Faulting Revealed by Rupture Directivity Analysis

2021 ◽  
Author(s):  
Xiaohui He ◽  
Hao Liang ◽  
Peizhen Zhang ◽  
Yue Wang
Keyword(s):  
South China ◽  
Source Parameters ◽  
Active Faults ◽  
Fault Zones ◽  
Strike Slip ◽  
P Wave ◽  
Complex Conjugate ◽  
South China Block ◽  
Rupture Directivity ◽  
Time Duration

Abstract The South China block has been one of the most seismically quiescent regions in China, and the geometries and activities of the Quaternary faults have remained less studied due to the limited outcrops. Thus, source parameters of small-to-moderate earthquakes are important to help reveal the location, geometry distribution, and mechanical properties of the subsurface faults and thus improve the seismic risk assessment. On 12 October 2019, two earthquakes (the Ms 4.2 foreshock and the Ms 5.2 mainshock) occurred within 2 s and are located in southern South China block, near the junction region of the large-scale northeast-trending fault zones and the less continuous northwest-trending fault zones. We determined the point-source parameters of the two events via P-wave polarity analysis and regional waveform modeling, and the resolved focal mechanisms are significantly different with the minimum 3D rotation angle of 52°. We then resolved the rupture directivity of the two events by analyzing the azimuth variation of the source time duration and found the Ms 4.2 foreshock ruptured toward north-northwest for ∼1.0 km, and the Ms 5.2 mainshock ruptured toward east-southeast (ESE) for ∼1.5 km, implying conjugate strike-slip faulting. The conjugate causative faults have not been mapped on the regional geological map, and we infer that the two faults may be associated with the northwest-trending Bama-Bobai fault zone (the Shiwo section). These active faults are optimally oriented in the present-day stress field (northwest-southeast) and thus may now be potentially accumulating elastic strain to be released in a future large earthquake.

Inversion of regional surface-wave spectra for source parameters of aftershocks from the Loma Prieta earthquake

1991 ◽  
Vol 81 (5) ◽  
pp. 1726-1736
Author(s):  
Susan L. Beck ◽  
Howard J. Patton
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Focal Mechanism ◽  
Source Parameters ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
P Wave ◽  
Wave Spectra ◽  
Short Period ◽  
First Motion

Abstract Surface waves recorded at regional distances are used to study the source parameters for three of the larger aftershocks of the 18 October 1989, Loma Prieta, California, earthquake. The short-period P-wave first-motion focal mechanisms indicate a complex aftershock sequence with a wide variety of mechanisms. Many of these events are too small for teleseismic body-wave analysis; therefore, the regional surface-waves provide important long-period information on the source parameters. Intermediate-period Rayleigh- and Love-wave spectra are inverted for the seismic moment tensor elements at a fixed depth and repeated for different depths to find the source depth that gives the best fit to the observed spectra. For the aftershock on 19 October at 10:14:35 (md = 4.2), we find a strike-slip focal mechanism with right lateral motion on a NW-trending vertical fault consistent with the mapped trace of the local faults. For the aftershock on 18 October at 10:22:04 (md = 4.4), the surface waves indicate a pure reverse fault with the nodal planes striking WNW. For the aftershock on 19 October at 09:53:50 (md = 4.4), the surface waves indicate a strike-slip focal mechanism with a NW-trending vertical nodal plane consistent with the local strike of the San Andreas fault. Differences between the surface-wave focal mechanisms and the short-period P-wave first-motion mechanisms are observed for the aftershocks analyzed. This discrepancy may reflect the real variations due to differences in the band width of the two observations. However, the differences may also be due to (1) errors in the first-motion mechanism due to incorrect near-source velocity structure and (2) errors in the surface-wave mechanisms due to inadequate propagation path corrections.

The kinematics of the Tan-Lu Fault zone during the Mesozoic-Palaeocene and its relations with the North China – South China block collision (Anhui Province, China)

2007 ◽  
Vol 178 (5) ◽  
pp. 353-365 ◽  
Author(s):  
Pierre Vergely ◽  
Ming Jin Hou ◽  
Young Ming Wang ◽  
Jacques-Louis Mercier
Keyword(s):  
Continental Crust ◽  
Fault Zone ◽  
South China ◽  
North China ◽  
Sedimentary Cover ◽  
Eastern China ◽  
Strike Slip ◽  
Late Triassic ◽  
South China Block ◽  
The North

Abstract The Tan-Lu Fault zone (TLFZ), often considered as a major sinistral strike-slip fault, extends in a NE to NNE direction for more than 2,000 km in eastern China. A structural analysis of the southern segment of the TLFZ (STLFZ) and surrounding areas enables us to propose the following evolution of this area during the Mesozoic-Palaeocene. The mid-Triassic NNW-SSE and late Triassic SSW-NNE to SSE-NNW strikes of the stretching lineations in the Zhangbaling massif favour ductile shears in a Zhangbaling metamorphic formation located along a ~NNE-SSW orientated “Tan-Lu margin”; this margin connected two margin segments situated north of the Dabie and Sulu belts. During the Mid-Late Triassic, the continental crust of the South China block (SCB) has been obliquely subducted along this margin below the North China block (NCB). We confirm that the SCB continental crust has been sliced and thrust toward the SSE and propose that the ductile thrusts have merged into the decollements of the sedimentary cover of the platform, forming the thrust-and-fold belt which has acted as a sinistral compressional transfer zone between the Dabie and Sulu collision belts. Thrusting and folding, under a N to NNE compression, affecting Jurassic deposits north and south of the Dabie Shan, indicate that the SCB/NCB collision has continued during the Jurassic. We show that a strike-slip tectonic regime occurred at that time, east of the STLFZ, which initiated as a sinistral continental transform fault between the Dabie and Sulu collisional belts. Dikes and strike-slip faults confirm that a ~NW-SE stretching was active during the basal early Cretaceous (~135–130 Ma), in and around metamorphic domes intruded by plutons. We show that strike-slip faulting, under a NW-SE compression-NE-SW tension, has been active subsequently, until the Aptian-? Early Albian (110/105 Ma), possibly until the Cenomanian (~95 Ma); at that time, the TLFZ has acted as a sinistral continental trans-current fault zone in eastern Asia. Subsequently, normal faulting, under a WNW-ESE extension, indicates that the TLFZ has been a normal fault zone during the Campanian-Palaeocene (~83–55 Ma), possibly until the Early Ypresian (~50 Ma). Sinistral offsets, in the order of several 100 of kilometres, on both sides of the TLFZ have been proposed; the present study does not support such large offset magnitudes.

Seismotectonics of the Portland, Oregon, region

1991 ◽  
Vol 81 (1) ◽  
pp. 109-130
Author(s):  
Thomas S. Yelin ◽  
Howard J. Patton
Keyword(s):  
Fault Zone ◽  
Moment Tensor ◽  
Fault Zones ◽  
Strike Slip ◽  
P Wave ◽  
Seismic Moment Tensor ◽  
Short Period ◽  
Dextral Strike Slip Fault ◽  
The University ◽  
Dextral Strike Slip

Abstract Portland, Oregon, lies in the southern half of an approximately rectangular basin measuring 30 by 50 km. Since 1969, there have been no earthquakes with M ≥ 4.0 in or on the margins of the Portland basin, but this level of seismicity may not be characteristic of the region. Using microseismicity data collected by the University of Washington regional short-period seismograph network for the period mid-1982 through 1989, we have determined P-wave focal mechanisms for four individual earthquakes and three groups of earthquakes. We have also relocated the 6 November 1962, MW = 5.2 Portland earthquake and analyzed regional surface-wave recordings of this event, using the seismic moment-tensor inversion technique. The results of these seismic analyses, along with geologic and other geophysical data, are integrated into a seismotectonic model of the Portland basin. The P-wave mechanisms are compatible with dextral strike-slip motion along approximately NW-striking fault zones bounding the eastern and western margins of the basin. We speculate that there is a dextral strike-slip fault zone, which we call the Frontal Fault Zone, along the eastern margin of the Portland basin. The western margin has been previously recognized as a zone of dextral strike-slip faulting, known as the Portland Hills Fault Zone. The epicenter of the 1962 earthquake is located between the two fault zones and lies approximately 15 km NE of downtown Portland. Our preferred mechanism is normal faulting on NE- or NNE-trending fault planes. These results support the hypothesis posed by previous investigators that the Portland basin is a pull-apart basin and are evidence for contemporary crustal extension between the Frontal and Portland Hills fault zones.

Spatio-temporal evolution and dynamic origin of Jurassic-Cretaceous magmatism in the South China Block

2021 ◽  
Vol 217 ◽  
pp. 103605
Author(s):  
Xianzhi Cao ◽  
Nicolas Flament ◽  
Sanzhong Li ◽  
R. Dietmar Müller
Keyword(s):  
South China ◽  
Temporal Evolution ◽  
South China Block ◽  
The South ◽  
Spatio Temporal ◽  
Cretaceous Magmatism

Empirical Equations of P-Wave Velocity in the Shallow and Semi-Deep Sea Sediments from the South China Sea

2021 ◽  
Vol 20 (3) ◽  
pp. 532-538
Author(s):  
Guanbao Li ◽  
Zhengyu Hou ◽  
Jingqiang Wang ◽  
Guangming Kan ◽  
Baohua Liu
Keyword(s):  
South China Sea ◽  
Wave Velocity ◽  
South China ◽  
Deep Sea ◽  
The South China Sea ◽  
P Wave ◽  
Empirical Equations ◽  
China Sea ◽  
P Wave Velocity ◽  
Deep Sea Sediments

Mesozoic tectonic evolution of the eastern South China Block: A review on the synthesis of the regional deformation and magmatism

2021 ◽  
pp. 104028
Author(s):  
Chunlin Li ◽  
Zongxiu Wang ◽  
Qingtian Lü ◽  
Yuanlong Tan ◽  
Leilei Li ◽  
...  
Keyword(s):  
South China ◽  
Tectonic Evolution ◽  
South China Block ◽  
Regional Deformation

CRUSTAL DEFORMATION STUDIES IN JAVA (INDONESIA) USING GPS

2009 ◽  
Vol 03 (02) ◽  
pp. 77-88 ◽  
Author(s):  
HASANUDDIN Z. ABIDIN ◽  
HERI ANDREAS ◽  
TERUYUKI KATO ◽  
TAKEO ITO ◽  
IRWAN MEILANO ◽  
...  
Keyword(s):  
Active Faults ◽  
Fault Zones ◽  
First Year ◽  
Horizontal Deformation ◽  
West Java ◽  
Plate Movement ◽  
Tsunami Earthquake ◽  
Second Year ◽  
Seismic Deformation ◽  
Large Earthquakes

Along the Java trench the Australian–Oceanic plate is moving and pushing onto and subducting beneath the Java continental crust at a relative motion of about 70 mm/yr in NNE direction. This subduction-zone process imposed tectonic stresses on the fore-arc region offshore and on the land of Java, thus causing the formation of earthquake fault zones to accommodate the plate movement. Historically, several large earthquakes happened in Java, including West Java. This research use GPS surveys method to study the inter-seismic deformation of three active faults in West Java region (i.e. Cimandiri, Lembang and Baribis faults), and the co-seismic and post-seismic deformation related to the May 2006 Yogyakarta and the July 2006 South Java earthquakes. Based on GPS surveys results it was found that the area around Cimandiri, Lembang and Baribis fault zones have the horizontal displacements of about 1 to 2 cm/yr or less. Further research is however still needed to extract the real inter-seismic deformation of the faults from those GPS-derived displacements. GPS surveys have also estimated that the May 2006 Yogyakarta earthquake was caused by the sinistral movement of the (Opak) fault with horizontal co-seismic deformation that generally was less than 10 cm. The post-seismic horizontal deformation of the July 2006 South Java tsunami earthquake has also been estimated using GPS surveys data. In the first year after the earthquake (2006 to 2007), the post-seismic deformation is generally less than 5 cm; and it becomes generally less than 3 cm in the second year (2007 to 2008).

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