任意点震源τ-P域地震图的解及AVO分析

用严格的数学推导得出τ-P域地震图的解析解。分析表明,τ-P域中地震图的子波可表示为激发震源子波的积分形式,决定反射波振幅的因素是平面波反射系数、反射界面上覆介质的波速以及方向因子。这些结果说明:1.在τ-P域进行AVO分析是可行的,并具有更高的精度;2.从一种新的途径可以进行速度函数的反演计算。     

A tectonic stress map of China and adjacent regions from earthquakes occurred during 2000～2004

Earthquake focal mechanism solutions provide the basic information about the present-day regional tectonics stress distribution, which controls the activities of crustal faults. Therefore, continued efforts for updating the da-tabase of earthquake focal mechanism solutions are quite valuable and important. The international lithosphere program initiated the ″world stress map project″ (Zoback, 1992) since 1980′s. During this project, worldwide studies and measurements of present-day regional…     

一类带阻尼项Duffing型方程周期解的存在性

考虑带有阻尼项的Duffing型方程的边值问题,在Banach空间上运用Leray-Schauder度理论证明其周期解的存在性。     

Isolated Periodic Orbits and Stability in Separable Potentials

A method for determining the main families of isolated periodic orbits and their characteristic exponents in planar potentials which are separated by a point transformation is proposed. Since these orbits are continued analytically with the same stability, these results are persistent under small perturbations. The method is applied to the two fixed centers problem, the Paul trap and the dipole expansion of an electrostatic potential. This revised version was published online in July 2006 with corrections to the Cover Date.     

Focal mechanisms of small earthquakes in the southeastern Brazilian shield: a test of stress models of the South American plate

Focal mechanisms of small earthquakes with magnitudes of about 3 in the SE Brazilian shield are calculated using S / P amplitude ratios. Low attenuation ( Q _p from 400 to 800) in the shield upper-crustal layers allowed sharp S arrivals to be recorded up to distances of 100 km. Besides P -wave polarities, SH -wave first motions were also used to constrain the nodal-plane orientations. Normal and reverse faulting mechanisms with strike-slip components were found. The inversion of four mechanisms to estimate the stress tensor indicated a strike-slip stress regime with roughly E–W-orientated σ ₁ and N–S σ ₃. Both the orientations and the shape factor ( φ =0.7) of the inverted stress are in excellent agreement with theoretical predictions for that part of Brazil from the driving-force model of Coblentz & Richardson (1996) . Good agreement with the nature of the stress, as well as its orientation, was also found for the model of Meijer (1995) . Both of these theoretical models include spreading stresses along the continent/ocean lithospheric transition. Because the earthquakes are more than 300 km from the continental shelf they should not be affected by the local flexural forces caused by sediment load in the marginal basins. The agreement between observed and theoretical stresses then confirms the importance of continental spreading forces in modelling intraplate stresses.     

端承桩在层状地基波动与辐射阻尼影响下的横向地震反应分析

通过对层状地层中端承桩的分析,建立了合理的几何,数学及力学模型。考虑层状地基ＳＨ与ＳＶ波波动及非线性辐射阻尼影响,应用Ｄｉｒａｃ广义函数及Ｗｉｎｋｌｅｒ地基理论计入各种动力,抗力,地震力及内力等,建立地基波动方程,桩振动方程,地基与桩耦合振动方程。给出了柯西型函数的自由振动解。利用非经典理论正交条件和卷积定理给出了强迫振动地震反应解析解,算例结果充分表明了动力特性及振动规律非常正确,充分体现了本文     

Relocation of shallow earthquakes in southern Alaska using Joint Hypocenter Determination method

A subset of 2660 shallow earthquakes (0–50 km) that occurred from 1988 to 1996 in south central Alaska between 155°W and 145°W and 59°N and 63°N was relocated using the joint hypocenter determination (JHD) method. Both P- and S-wave observations recorded by the regional seismic network were used. Events were relocated in twenty different groups based on their geographic location and depth using two velocity models. As a result of the relocation, the majority of the hypocenters shifted downward, while the epicenter locations did not change significantly. The distribution of the shallow subduction zone earthquakes indicates the existence of two seismically independent blocks, with one block occupying the northeastern part and the other occupying the central and western parts of the study area. The boundary between the blocks is marked by a 15 to 20 km wide seismicity gap to the southeast of 149.5°W and 62°N. The analysis of the fault plane solutions for shallow subduction zone earthquakes shows that an overwhelming majority of the solutions represent normal, oblique-normal or strike-slip faulting with predominant WNW-ESE orientation of T-axes. This indicates a down-dip extensional regime for the subducting slab at shallow depths. Very few earthquakes yielded fault plane solutions consistent with thrusting on a contact zone between the overriding and subducting plates. This result may be an indication that currently either the strain energy is not released at the contact zone or it is associated with aseismic motion.     

On the galactic motion

A certain potential function is studied as a possible model for the galactic potential. Some solutions are obtained. Also the numerical study of some of the orbits and their stability is carried out.     

Periodic solutions around the collinear langrangian points in the photo gravitational restricted three-body problem: Sun-Jupiter case

The evolution of the periodic orbits around the collinear equilibrium positions, belonging to the Strömgren families a, b and c, with the radiation pressure parameter of the more massive body is studied in the Sun-Jupiter system. These families are determined for a single value of the radiation pressure parameter and particularly when the radiation force of the more massive body is equal to one half of the gravitational attraction. Then the critical stability orbits of each family are transferred with the radiation parameter. The stability of each periodic solution is also studied.     

Dynamics of a satellite orbiting a planet with an inhomogeneous gravitational field

We study the dynamics of a satellite (artificial or natural) orbiting an Earth-like planet at low altitude from an analytical point of view. The perturbation considered takes into account the gravity attraction of the planet and in particular it is caused by its inhomogeneous potential. We begin by truncating the equations of motion at second order, that is, incorporating the zonal and the tesseral harmonics up to order two. The system is formulated as an autonomous Hamiltonian and has three degrees of freedom. After three successive Lie transformations, the system is normalised with respect to two angular co-ordinates up to order five in a suitable small parameter given by the quotient between the angular velocity of the planet and the mean motion of the satellite. Our treatment is free of power expansions of the eccentricity and of truncated Fourier series in the anomalies. Once these transformations are performed, the truncated Hamiltonian defines a system of one degree of freedom which is rewritten as a function of two variables which generate a phase space which takes into account all of the symmetries of the problem. Next an analysis of the system is achieved obtaining up to six relative equilibria and three types of bifurcations. The connection with the original system is established concluding the existence of various families of invariant 3-tori of it, as well as quasiperiodic and periodic trajectories. This is achieved by using KAM theory techniques.