Gravity changes and surface deformations due to faults with different geometry

IntroductionNowadaystheprecisionofgravitymeasurementisupto10xlo--8InjsZ(Okubo,1992),theprecisionofaltimetryisoftheorderofmm,andtheprecisionofrelativemeasurementinhorizontaldirectionusingGPStechniquesreaches(0.01--0.001)x10ed(Liu,etal,1998).Thegravitychangesinducedbyalargeearthquake(e.g.,Tangshanearthquakeof1976)canbetensorevenhundredsof10--8m/s',andthemaximumdisplacementinhorizontalandverticaldirectioncreatedbyitalwaysexceedI.0m(Chen,etal,1979,1980,Zhang,etal,1981).Therefore,structuresrela…     

Internal co-seismic deformation and curvature effect based on an analytical approach

In this study, we present a new method to compute internal co-seismic deformations of a homogeneous sphere, based on our previous approach (Dong et al. 2016). In practical numerical computations, we consider a strike-slip point source as an example, and compute the vertical co-seismic displacement on different internal spherical surfaces (including the Earth surface). Numerical results show that the internal co-seismic deformations are generally larger than that on the Earth surface; especially, the maximum co-seismic displacement appears around the seismic source. The co-seismic displacements are opposite in sign for the areas over and beneath the position of the seismic source. The results also indicate that the curvature effect of the internal deformation is pretty large, and larger than that on the Earth surface. The results indicate that the dislocation theory for a sphere is necessary in computing internal co-seismic deformations.     

新丰江水库库区形变测量与地震活动关系探讨

广东省新丰江水库地区1962年3月19日发生 Ms=6.1的地震.地震前后,库坝区分别布设了水准测量网和三角测量网.形变测量具有精度高、测期密的特点.本文通过对不动点的处理,得出新的形变场并讨论了它的特点;根据各相邻期的三角测量结果计算了各三角形的主应变;依据地震时的应变对一次5.3级的地震的发震断层作了反演.结果表明,地壳水平形变与新丰江水库地区4级以上地震有明显的关系,垂直形变与这些地震无明显关系.      

Tsunami and mechanism of great earthquakes

The relation between tsunamis and sea-bottom deformations associated with the Kurile Islands earthquake of 1969 and the Tokachi-Oki earthquake of 1968 is studied on the basis of a fairly complete set of seismological and tsunami data. The seismic results are included in the calculation of static crustal deformations. The calculated deformations are compared with the tsunami source area as obtained by the inverse refraction diagram, the first motion of tsunami waves, and the height of the sea-level disturbance at the source. It is found that such deformations as predicted by the seismic results can quantitatively explain the source parameters of tsunamis. These findings strongly favor the idea that tsunamis are generated by tectonic deformations rather than by large submarine landslides and slumps. This conclusion is supported by additional analyses for the 1964 Niigata, 1944 Tonankai, 1933 Sanriku earthquakes. For the 1946 Nankaido earthquake, the source deformation responsible for the tsunami generation is of much greater magnitude than that for seismic waves.     

Microgravity and height changes caused by volcanic activity: Four

Microgravity measurements and levelling surveys on volcanoes are not always easy to make, but are useful for studying volcanic processes quantitatively. Gravity changes associated with volcanic activity are not always significant. Precision of microgravity measurements depend critically on the procedures adopted, and those applied in the present paper are described. Levelling technique is now orthodox, and some empirical laws relating ground deformation to volcanic activity are deduced from the accumulated data. Gravity changes occur at the same time and places as ground deformations. The relationship between microgravity and height changes are discussed from the standpoint of analyzing the data obtained on volcanoes. The observational results obtained on four volcanoes in Japan are separately analyzed because each volcano exhibits different patterns of gravity changes and deformations. During the 1977–1982 activity of Usu volcano, deformation was accompanied by microgravity changes frequently observed at a particular benchmark at the base of the volcano for about five years. The gravity changes prove to be not a direct effect of magma movements but to be caused by the deformations of ground strata and aquifers around the benchmark. The 1983 eruption of Miyakejima volcano was associated with local gravity changes around the eruptive fissures due to magma intrusion which was approximately modelled. Similarly the 1986 eruption of Ooshima volcano caused gravity changes on the volcano, but these were poorly correlated with elevation changes and their origins were not uniquely interpreted. To detect gravity changes associated with the activity of Sakurajima volcano, an equigravity point was selected at the north of the volcano besides the gravity points on and around the volcano itself. The probable gradual accumulation of magmas beneath the volcano for eight years is substantiated by observed microgravity and elevation changes.     

利用高频GPS进行地表同震位移监测及震相识别

结合日本3.11大地震,利用近震区和远震区若干测站的高频GPS观测数据,采用动态精密单点定位技术分析了强震时复杂的地表运动时序,获得了地表同震位移.在此基础上提出利用S变换对高频GPS地震波进行震相识别,有效拾取了P波初至,反演了P波传播速度并与地震仪数据、USGS提供的参考值进行了对比和分析,为后续地震应急、地震预警提供了重要的、科学的决策依据.     

Nonlinear elastic and inelastic spectra with inherent and supplemental damping

During severe seismic events, structures designed according to current standards yield and develop inelastic deformations. While the acceleration responses are limited by the yielding strength, these structures develop permanent deformations (and possible damage) due to such yielding. Spectra developed for inelastic structures can help in determining the desired yield levels and the associated inelastic deformations. Some structures made of special materials or equipped with innovative structural systems may yield, but can recover the deformation upon unloading and, thus, may avoid permanent deformations. These structures are known as nonlinear elastic. Often the post yielding excursions are very large and may exceed their toughness (or deformability). By introducing damping in form of supplemental devices, it is possible to control such deformations and keep them within acceptable limits. Spectra for such nonlinear elastic structures and inelastic structures are developed herein, by considering both inherent and supplemental damping. The difference between the two types of damping is addressed both theoretically and numerically. Design examples of several simple structures using the newly developed spectra are presented, which illustrate the importance of lower strength and damping in these nonlinear elastic or inelastic systems. Copyright © 2013 John Wiley & Sons, Ltd.     

华北东部地区的共轭地震破裂与地质构造

本文研究了华北东部地区地震与地质构造的关系。对该地区１９６６－１９７６年发生的５次强震的震源机制、地震形变一、余震活动、极震区等震线、地形变制量资料进行了综合分析，发现华北东部地区地震破裂具有在强度上不对称的共轭剪切破裂特征；地震破裂相对于地质构造具有突出的新生性。     

A review of considerations on seismic safety of embankments and earth and rock-fill dams

An attempt has been made to summarise the methods of approach used in assessing the dynamic behaviour and safety of earth and rock-fill dams under seismic shaking until about the present time, from the soil engineer's point of view. Shortcomings of the pseudo-static method, procedures to estimate the permanent deformations, liquefaction effects, and experience gained from the previous events have been reviewed. Observing that the most important cause of instability is the occurence liquefaction during ground motions, cyclic approach and steady-state approach in assessing the liquefaction potential have been addressed and recent practical approaches of analysis and design have been referred. It has been found noteworthy to recall that incidence of failure or serious damage to well-engineered dams has not been experienced, even under strong ground shaking.     

Physics of basic motions in asymmetric continuum

We consider the advantages of a formalism based on concept of the asymmetric continuum and we present some equivalence theorems relating it to the asymmetric elasticity and to micropolar and micromorphic theories as founded by Nowacki, Cosserats and Eringen. We consider the basic processes in an asymmetric continuum which could be reduced to the point basic motions/deformations. The co-action of spin and shear motions is assumed to play the main role in fracturing process, while the constitutive relation between the antisymmetric stresses and rotations replaces the friction constitutive law.     

A new approach for distinguishing different deformation trend blocks with displacement observations

Introduction The accumulation of high precision GPS data has great significance for understanding and explaining crustal movement and establishing the geodynamical model correctly. However, it is an important basic task to study block movement with the displacement data which covers the datum influence information, as well as the deformation information of the block and abnormal deforma-tion information in the block such as fault or zone of fracture and so on. Firstly steady or com-parativel…     

Finite fault analysis and near-field dynamic strain and rotation estimates due to the 11/05/2011 (Mw5.2) Lorca earthquake,south-eastern Spain

The 11/5/2011 Lorca, Spain earthquake (Mw \(\,=\,\) 5.2) and related seismicity produced extensive damage in the town of Lorca and vicinity. During these earthquakes, evidence of rotations and permanent deformations in structures were observed. To analyze these aspects and study the source properties from the near-field, the displacement time histories were obtained including the static component at Lorca station. Displacement time histories were computed by an appropriate double time integration procedure of accelerograms. Using these data, the foreshock and mainshock slip distributions were calculated by means of a complete waveform kinematic inversion. To study the dynamic deformations, the 3D tensor of displacement gradients at Lorca station was first estimated by a single station method. Using the finite fault inversion results and by means of a first order finite difference approach, the dynamic deformations tensor at surface was calculated at the recording site. In order to estimate the distribution of the peak dynamic deformations, the calculation was extended to the close neighboring area of the town. The possible influence of the near-field deformations on the surface structures was analyzed.     

Wave coupling between the Tianshan orogen and the deformations in its south and north foreland basins in Cenozoic

Attention has been paid to the deformations in the south and north foreland basins of the Tianshan Mountains and their relations to the tectonic movements of the mountains. Based on the seismic data interpretation and field work,the tectonic features,tectonic styles,controlling factors of deformation,deformation time,and their relationships in the three tectonic units were comparably studied. The Ce-nozoic deformations in the two foreland basins were characterized by zonation from south to north,segmentation from west to east,and layering from deep to shallow. The tectonic styles are compres-sive ones,including both basement-involved and cover-detaching. The two foreland basins underwent several times of deformation in Cenozoic and the deformations were transmitted from the Tianshan orogen to the inner basin. The deformation dynamics of the south and north foreland basins of the Tianshan Mountains can be represented by dynamics of orogenic wedges. In terms of the deformations of the wedges with wave-like features,the concept of a wave orogenic wedge was put forward,and a double wave orogenic wedge model was established.     

Effects of supplemental viscous damping on seismic response of asymmetric-plan systems

Coupling between lateral and torsional motions may lead to much larger edge deformations in asymmetric-plan systems compared to systems with a symmetric plan. Supplemental viscous damping has been found to be effective in reducing deformations in the symmetric-plan system. This investigation examined how supplemental damping affects the edge deformations in asymmetric-plan systems. First, the parameters that characterize supplemental viscous damping and its plan-wise distribution were identified, and then the effects of these parameters on edge deformations were investigated. It was found that supplemental damping reduces edge deformations and that reductions by a factor of up three are feasible with proper selection of system parameters. Furthermore, viscous damping may be used to reduce edge deformations in asymmetric-plan systems to levels equal to or smaller than those in the corresponding symmetric-plan system. © 1998 John Wiley & Sons, Ltd.     

Field of vertical crustal deformation in North China and the feature of its dynamic evolution

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Deformation caused by the 2011 eastern Japan great earthquake monitored using the GPS single-epoch precise point positioning technique

Crustal deformation can provide constraints for studying earthquake rupture and shock wave transmission for the Mw9.0 eastern Japan great earthquake. Using the single-epoch precise point positioning (PPP) method and the appropriate positioning flow, we process GPS data from six IGS (International GNSS Service) sites (e.g., MIZU, TSK2, USUD, MTKA, AIRA and KSMV) located in Japan and obtain the positioning results with centimeter scale precision. The displacement time series of the six sites are analyzed using the least squares spectral analysis method to estimate deformations caused by the Mw9.0 mainshock and the Mw7.9 aftershock, and the cumulative displacements after 1 day. Mainshock displacements at station MIZU, the nearest site to the mainshock in the North (N), East (E), and Up (U) directions, are ?1.202 m, 2.180 m and ?0.104 m, respectively, and the cumulative deformations after 1 day are ?1.117 m, 2.071 m and ?0.072 m, respectively. The displacements at station KSMV, the nearest site to the Mw7.9 aftershock in the N, E and U directions, are ?0.032 m, 0.742 m and ?0.345 m, respectively. The other sites obviously experienced eastern movements and subsidence. The deformation vectors indicate that the horizontal displacements caused by the earthquake point to the epicenter and rupture. Elastic bounds evidently took place at all sites. The results indicate that the crustal movements and earthquake were part of a megathrust caused by the Pacific Plate sinking under the North American Plate to the northeast of Japan island arc.     

Active blocks and their deformations derived from the velocity field in North China

Based on the horizontal movement velocities and their error estimations of 144GPS stations in North China de-duced from the results obtained from multiple GPS measurements carried out in the period of 1992-2001,the horizontal deformation in the area is stuklied.The movements,entire deformations,local deformations,activeity patterns and intensities along the boundary zones are derived.And then the risk of strong earthquake in the area is estimated.In the research,the horizontal displacement observations can be considered as the sum of three parts.The first part is the entire motion following Eurasian plate,which can be derived from NUVAL-IA model;the second part is the relative motions and deformations between the sub-tectonic blocks in the studied area,which can be derived from a set of displacement observations determined by the expanded QUAD method in the paper;the third part is the local deformations and errors in the sub-tectonic blocks,which can be described as the inhomoge-neous strains of the block.The method and results are introduced in detail in the paper.     

Post-glacial rebound and present-day three-dimensional deformations

The WEGENER^† activities related to the study of post-glacial rebound are presented together with a review of the present state-of-the-art in this study field. Post-glacial rebound research is an unique tool for studying the viscoelastic behaviour of the Earth's mantle on time scales of thousands of years. The viscosity structure of the Earth's mantle determined from an inversion of observations of glacially induced deformations is a basic requirement for modelling long-term phenomena such as the convection in the Earth's mantle, and for better understanding unsolved questions such as the nature of the mantle discontinuities or the vertical scale of convection.First, an introduction to the scientific background is given, and the three principal ingredients for post-glacial rebound studies, namely the ice model, the Earth model, and the observations are briefly considered. For the ice model, the uncertainties due to a trade-off between ice model and Earth rheology are outlined. The different approaches used to model the Earth and its deformations in post-glacial rebound studies are discussed emphasising the preliminary nature of the derived rheologies and depth dependencies. The observations, in particular the relative sea-level changes and three-dimensional surface deformations, are described with special emphasis on observational gaps. Based on the discussion of the ingredients, an outline of the future developments in post-glacial rebound research is attempted with particular emphasis on the Earth model and the theory of deformations.For several decades extreme efforts have been made to precisely monitor the land uplift in Scandinavia. However, for the height component the existing data still are associated with large uncertainties while reliable data on the horizontal component are practically nil. The ongoing long-term (longer than ten years) spacegeodetic measurements are likely to provide the three-dimensional deformations with the spatial resolution and accuracy required in order to substantially contribute to post-glacial rebound studies. Thus, present-day three-dimensional deformations of the Earth's surface beneath and around the former ice sheets as a constraint for the mantle rheology and viscosity structure will increasingly become important as they become known from space-geodetic measurements with high spatial resolution and an accuracy approaching the mm/a-level.     

On the origin of subhorizontal compressive stresses and deformations in a mobile belt

Subhorizontal compressive stresses and deformations play a leading role in the formation of the tectonic structure of mobile belts. These stresses and deformations can arise due to either a lateral convergence of lithospheric plates, subplates, and other lithospheric units or an increase in the volume of layered rocks between fixed walls. Results of geodetic measurements indicate a great role of the latter process.     

Mapping three-dimensional co-seismic surface deformations associated with the 2015 M_W7.2 Murghab earthquake based on InSAR and characteristics of crustal strain

Three-dimensional(3 D) co-seismic surface deformations are of great importance to interpret the characteristics of coseismic deformations and to understand the geometries and dynamics of seismogenic faults. In this paper, we propose a method for mapping 3 D co-seismic deformations based on InSAR observations and crustal strain characteristics. In addition, the search strategy of correlation points is optimized by adaptive correlation distance, which greatly improves the applicability of the proposed method in restoring deformations in decorrelation areas. Results of the simulation experiment reveal that the proposed method is superior to conventional methods in both the accuracy and completeness. The proposed method is then applied to map the 3 D co-seismic surface deformations associated with the 2015 MW7.2 Murghab earthquake using ascending and descending ALOS-2 PALSAR-2 images. The results show that the seismogenic fault is the Sarez-Karakul fault(SKF), which is dominated by NE-SW strike slips with an almost vertical dip angle. The north section and the south segment near the epicentre have obvious subsidence along with a southwestward motion in the northwest wall, and the southeast wall has northeast movement and surface uplift trend along the fault zone. The strain field of the earthquake is also obtained by the proposed method. It is found that the crustal block of the seismic area is obviously affected by dilatation and shear forces, which is in good agreement with the movement character of the sinistral slip.