Study on the pattern and mode of vertical crustal deformation during the seismogenic process of intraplate strong earthquakes

In this paper,the data of vertical crustal deformations associated with the Xingtai,Haicheng,Tangshan and Datong strong earthquakes in North China Block have been processed,analyzed and studied.The result shows that the seismogenic processes of strong earthquakes are accompanied by an evolution of crustal deformation as follows: ① The area of crustal deformation anomaly should be large in radius and extensive in range. ② There are both the 'field' and 'source' of crustal deformation anomaly,with the 'source' existing inside the'field' but differing from the 'field' distinctly. ③ The evolution process includes a number of steps.Firstly, movements in the 'field region transform from the normal state to an anomalous state to start the formation of field precursors.Secondly,movements in the 'source' region become outstandingly remarkable. Thirdly,anomalies in the 'field' region that surrounds the 'source' become increasingly intense.Fourthly,the 'source' region enters a state of immobilized-movement.Finally,an earthquake occurs. ④ There are usually one or more areas where the anomaly field forms a special pattern,mostly a four-quadrant distribution.The area which is'activated' first but becomes 'immobilized' afterwards often coincides with the source area.⑤ The appearance of an obviously immobilized area inside the obviously activated area is a precursory feature which suggests that an earthquake is impending.⑥ The longer the duration of immobilized-movement,the higher the magnitude of earthquake would be.The above might be the basic mode of vertical crustal deformation during the seismogenic process of strong intraplate earthquakes.

Multifractal characteristics of spatiotemporal distribution of earthquakes in intraplate and interplate regions

This paper analyzes the multifractal characteristics of spatio-temporal distribution of generalized strain release of earthquakes （GSRE） occurred in the eastern and western Chinese mainland （as an instance of intraplate region）, Taiwan region and New Zealand （as an instance of interplate region）. The results show that the multifractal characteristics of GSRE are closely related to the geodynamic environment. For the temporal distribution of strong events, the clustering feature is more evident in the interplate regions than that in the intraplate regions, while for small and moderate events, this difference is ambiguous. For the spatial distribution of strong earthquakes, the clustering feature is usually clearer in the intraplate regions than that in the interplate regions, while for small and moderate events, the case is just opposite.

A 15-year-Long catalog of seismicity in the Eastern Tennessee Seismic Zone(ETSZ)using matched filter detection

We present a detailed catalog of 13671 earthquakes in the Eastern Tennessee Seismic Zone(ETSZ)that spans January 1,2005 to July 31,2020.We apply a matched filter detection technique on over 15 years of continuous data,resulting in arguably the most complete catalog of seismicity in the ETSZ yet.The magnitudes of newly detected events are determined by computing the amplitude ratio between the detections and templates using a principal component fit.We also compute the b-value for the new catalog and comparatively relocate a subset of newly detected events using XCORLOC and hypoDD,which shows a more defined structure at depth.We find the greatest concentration along and to the east of the New York-Alabama Lineament,as defined by the magnetic anomaly,supporting the argument that this feature likely is related to the generation of seismicity in the ETSZ.We examine seismicity in the vicinity of the Watts Bar Reservoir,which is located about 5 km from the epicenter of the M_(W) 4.4 December 12,2018 Decatur,Tennessee earthquake,and find possible evidence for reservoir modulated seismicity in this region.We also examine seismicity in the entire ETSZ to search for a correlation between shallow earthquakes and seasonal hydrologic changes.Our results show limited evidence for hydrologicallydriven shallow seismicity due to seasonal groundwater levels in the ETSZ,which contradicts previous studies hypothesizing that most intraplate earthquakes are associated with the dynamics of hydrologic cycles.

Local Magnitude Study of the Seismic Activity on Itacarambi,MG

The importance of studying the local magnitude related to seismic activity occurred recently in the region of Itacarambi, state of Minas Gerais, is due to the fact that these were earthquakes of intraplate origin. From the study of [1] and the relation between local magnitude and seismic signal duration, was performed a data analysis obtained in the same region, on the period between October/2007 and June/2008, in which we can estimate the equation MD = 2.153 (±0.072) LogD – 1.925 (±0.132) to calculate the magnitude of local duration. We can also estimate one value for the b parameter using the equation LogN = a – bMD from a frequency-magnitude study. It was found the value of b = 0.826 (±0.020) for the general activity of Itacarambi, MG, that is within the universal range proposed by [2].

ComprehensiveanalysesofseismicsourcelayerinXingtaiandTangshanseismicregionsandtheconditionsofmediaab

Statistic analyses of sectional focal depth frequency relation for 1739 M S≥4.0 events in North China, 541 M S≥4.0 events in Xingtai seismic region and 999 M S≥4.0 events in Tangshan seismic region have been carried out for the first step of the study. Then the sectional focal depth frequency diagrams (H N diagram) for each region were obtained. The study shows that: (1) The intraplate earthquakes in North China occur within the continental crust, and are mainly concentrated within a certain depth range of the middle and upper crust, making up a seismic source layer; (2) The seismic source layer consists of a main layer and an auxiliary layer adjacent to it. The tops and bottoms of the main and auxiliary layers correspond to the G and C, as well as to B and G geologic boundaries respectively; (3) The H N diagrams for Xingtai and Tangshan seismic regions are significantly different from each other, indicating the regionality and localization of the seismic source layers; (4) DSS and MTS observations show that the regionality and localization of the seismic source layer depend mainly on the environment of the deep structures of the region; (5) The seismic source layer is a substance of medium layer, which can be related to the brittle ductile transition zone within the crust. The seismic source layer is also a stress conducting layer. As the media above and below this layer are subjected to failure or flowage, then the stress will concentrate in the stress conducting layer, in which the earthquake occurs.

The source rupture feature of the southern Taiwan Straits earthquake of September 16，1994 （Ms7．3） ＆ the analysis of earthquake circumstance in southeastern coast of China

According to the source mechanism of the main shock and the distribution feature of the aftershocks occurring in the southern Taiwan Straits on Sept. 16, 1994, in this paper the authors analysed the source rupture feature of the major earthquake, demonstrated that this seismic sequence possessed the charateristics of a large intraplate earthquake. And according to the seismotectonic background and the historical seismicity in the area, the authors clarified the active characteristics of the seismically active belts along northwestern direction and analysed preliminarily the earthquake circumstance in the southeastern coast of China.

The relationship between crust-mantle structural ratio and seismic activity

In this paper the differences and characteristics of the degree of seismic activities of various tectonic blocks and the different parts within the blocks in the eastern part of the Chinese mainland (to the east of 105°E) have been studied. Based on the results, the crust-mantle structural factors which caused these differences have further been studied from the inner and deep part of the plate. The ratio between the crustal and lithospheric thicknesses, i. e. the so-called crust-mantle structural ratio R, has been calculated. The result has shown that the magnitude of R has a close relation to the degree of seismic activity. The R-value implies the state of the movement of crust-mantle materials and the degree of interaction between the crust and mantle through convection and intrusion.