Variations of crustal thickness and average Vp/Vs ratio beneath the Shanxi Rift, North China, from receiver functions

AbstractThe Shanxi Rift located in the central part of the North China Craton (NCC) as a boundary between the Ordos block and the Huabei basin. The Shanxi graben system is a Cenozoic rift and originated from back-arc spreading related to westward subduction of the western Pacific and far field effects caused by northward subduction of the Indian plate. It has also had strong earthquake activity in China since the Quaternary. To investigate the tectonic evolution and tectonic setting of strong earthquakes in the Shanxi Rift, we apply the receiver function $$H$$ H -$$\kappa$$ κ stacking method to determine the crustal thickness and average Vp/Vs ratio in the area. The results show that the thickness of the crust increases from approximately 30 km in the Huabei basin to approximately 47 km in the Yinshan Mountains with a close correlation between the Moho depth and topography. The Yuncheng, Linfen and Taiyuan grabens have varying degrees of crustal thinning. The crustal average Vp/Vs ratio in the Shanxi Rift has significant heterogeneity; the high Vp/Vs ratio (~ 1.85) are found in the Datong and Yuncheng grabens, and Vp/Vs ratio of the Taiyuan and Linfen grabens is approximately 1.75 which close to the global average value ~ 1.782. Combining the observations in this study with previous research, we suggest that the grabens in the Shanxi Rift experienced extensional deformation from south to north and that the possibility of strong earthquakes in the central part of the Shanxi seismic belt is greater than that on the northern and southern sides.

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Crustal Anisotropy Beneath the Trans-North China Orogen and its Adjacent Areas From Receiver Functions

Frontiers in Earth Science ◽

10.3389/feart.2021.753612 ◽

2021 ◽

Vol 9 ◽

Author(s):

Xiaoming Xu ◽

Zhifeng Ding ◽

Li Li ◽

Fenglin Niu

Keyword(s):

Crustal Deformation ◽

North China ◽

Receiver Function ◽

Bouguer Anomaly ◽

Receiver Functions ◽

Seismic Hazards ◽

Moho Depth ◽

Tectonic Deformation ◽

Bohai Bay ◽

Crustal Anisotropy

As an important segment of the North China Craton, the Trans-North China Orogen (TNCO) has experienced strong tectonic deformation and magmatic activities since the Cenozoic and is characterized by significant seismicity. To understand the mechanism of the crustal deformation and seismic hazards, we determined the crustal thickness (H), Vp/Vs ratio (κ) and crustal anisotropy (the fast polarization direction φ and splitting time τ) beneath the TNCO and its adjacent areas by analyzing receiver function data recorded by a dense seismic array. The (H, κ) and (φ, τ) at a total of 309 stations were measured, respectively. The Moho depth varies from ∼30 km beneath the western margin of the Bohai bay basin to the maximum value of ∼48 km beneath the northern Lüliang Mountain, which shows the positive and negative correlations with the elevation and the Bouguer anomaly. The average φ is roughly parallel to the strikes of the faults, grabens and Mountains in this study area, whereas a rotating distribution is shown around the Datong-Hannuoba volcanic regions. Based on the φ measured from the Moho Ps and SKS/SKKS phases, we propose that the crustal deformation and seismic hazards beneath the TNCO could be due to the counterclockwise rotation of the Ordos block driven by the far-field effects of the India-Eurasian collision.

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Tectonic Environments of Strong Earthquakes in the North China Region

Seismological Research Letters ◽

10.1785/gssrl.59.4.241 ◽

1988 ◽

Vol 59 (4) ◽

pp. 241-246 ◽

Cited By ~ 1

Author(s):

Ma Zongjin ◽

Wang Xiaoqing

Keyword(s):

North China ◽

Tectonic Setting ◽

Plate Boundaries ◽

Seismic Region ◽

Strong Earthquakes ◽

The North ◽

Continental Plate ◽

Tectonic Zones ◽

Seismotectonic Zones ◽

Shallow And Deep Structures

Abstract The North China Seismic Region is not a typical intraplate seismic region. Not only does it show a pervasive neotectonic influence of global plate geodynamics, but it also displays an atypical seismic activity rate, especially for strong earthquakes, for a region far from plate boundaries. It is obvious that the seismicity is related to the active seismotectonics and geodynamics of the deforming interior of a continental plate. The features of the seismotectonic zones and the tectonic setting of magnitude 6.0 or greater earthquakes in the region are discussed here. We conclude that strong earthquakes occur mainly in places where NE-trending main and NW-trending auxiliary tectonic zones intersect. Three types of mechanisms are suggested which differ according to the characteristics of different seismotectonic zones and which relate to different shallow and deep structures. These observed types of strong earthquakes in North China may represent the main categories of continental intraplate seismicity.

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Structure of S-Wave Velocity in the Crust-Upper Mantle and Tectonic Setting of Strong Earthquakes Beneath Yunnan

Chinese Journal of Geophysics ◽

10.1002/cjg2.1611 ◽

2011 ◽

Vol 54 (3) ◽

pp. 286-298 ◽

Cited By ~ 2

Author(s):

Xiao-Man ZHANG ◽

Jia-Fu HU ◽

Yi-Li HU ◽

Hai-Yan YANG ◽

Jia CHEN ◽

...

Keyword(s):

Wave Velocity ◽

Upper Mantle ◽

Tectonic Setting ◽

S Wave ◽

Strong Earthquakes

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Strong earthquake activity influenced by solar flare intensity

10.5194/egusphere-egu21-3078 ◽

2021 ◽

Author(s):

Gerald Duma

Keyword(s):

Solar Flares ◽

Strong Earthquake ◽

Temporal Variations ◽

Seasonal Effect ◽

Earthquake Activity ◽

Strong Earthquakes ◽

International Service ◽

Earthquake Frequency ◽

Magnetic Index ◽

Magnetic Disturbances

Based on the comprehensive earthquake catalogue USGS ( HYPERLINK&#160; https://earthquake.usgs.gov) the paper demonstrates that strong earthquake activity, seismic events with M&#8805;6, exhibits a seasonal trend. This feature is the result of&#160; analyses of earthquake data for the N- and S- Earth Hemisphere in period 2010-2019. It can be shown also for single earthquake prone regions as well, like Japan, Eurasia, S-America.Any seasonal effect suggests an external influence. In that regard, one can think also of a solar-terrestrial effect, that is suggested already in several studies (e.g&#160; M.Tavares, A.Azevedo, 2011; D.A.E. Vares, M.A.Persinger,2014; G.Duma, 2019). This assumption leads to the question: Which dynamic process can cause a trigger effect for strong earthquakes in the Earth's lithosphere.In this study the intensity of solar flares and the resulting radiation, the solar wind, towards the Earth was taken into account. An appropriate parameter which has been regularity measured and reported for many decades and which reflects the intensity of solar radiation is the magnetic index Kp. It is measured at numerous geomagnetic observatories and describes the magnetic disturbances in nT within 3 hour intervals, respectively. Averages of all the measured 3-hour values are then published as Kp, therefore considered a planetary parameter (International Service of Geomagnetic Indices ISGI,France).The temporal variations of strong earthquake activity over 10 years and their energy release was compared with the above mentioned index Kp. Actually, a distinct correlation between the two quantities, Kp and earthquake frequency, resulted in cases of different regions as well as globally.&#160;Another essential result of the study is that maxima of Kp preceed those of earthquake activity by about 60 to 80 days in most cases. The mechanism has not yet been modeled satisfactorily.

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