Reflection Of Seismic Waves Research Articles

Grid-characteristic method on embedded hierarchical grids and its application in the study of seismic waves

The grid-characteristic method on a sequence of embedded hierarchical grids is used to study the reflection and diffraction of elastic seismic waves propagating from an earthquake hypocenter to the Earth’s surface. More specifically, the destruction caused by seismic waves in complex heterogeneous structures, such as multi-story buildings, is analyzed. This study is based on computer modeling with the use of the grid-characteristic method, which provides a detailed description of wave processes in heterogeneous media, takes into account all types of emerging waves, and relies on algorithms that perform well on the boundaries of the integration domain and material interfaces. Applying a sequence of hierarchical grids makes it possible to simulate seismic wave propagation from an earthquake hypocenter to ground facilities of interest—multi-story buildings—and to investigate their seismic resistance.

Diffraction separation by plane-wave prediction filtering

Seismic data processing typically deals with seismic wave reflections and neglects wave diffraction that affect the resolution. As a general rule, wave diffractions are treated as noise in seismic data processing. However, wave diffractions generally originate from geological structures, such as fractures, karst caves, and faults. The wave diffraction energy is much weaker than that of the reflections. Therefore, even if wave diffractions can be traced back to their origin, their energy is masked by that of the reflections. Separating and imaging diffractions and reflections can improve the imaging accuracy of diffractive targets. Based on the geometrical differences between reflections and diffractions on the plane-wave record; that is, reflections are quasi-linear and diffractions are quasi-hyperbolic, we use plane-wave prediction filtering to separate the wave diffractions. First, we estimate the local slope of the seismic event using planewave destruction filtering and, then, we predict and extract the wave reflections based on the local slope. Thus, we obtain the diffracted wavefield by directly subtracting the reflected wavefield from the entire wavefield. Finally, we image the diffracted wavefield and obtain high-resolution diffractive target results. 2D SEG salt model data suggest that the plane-wave prediction filtering eliminates the phase reversal in the plane-wave destruction filtering and maintains the original wavefield phase, improving the accuracy of imaging heterogeneous objects.

A seismic shift in continental tectonic plates.

Seismology provides an improved estimate for thickness of the continents

Propagation of SH-Waves Through Non Planer Interface between Visco-Elastic and Fibre-Reinforced Solid Half-Spaces

AbstractIn the propagation of seismic waves through layered media, the boundaries play crucial role. The boundaries separating the different layers of the earth are irregular in nature and not perfectly plane. It is, therefore, necessary to take into account the corrugation of the boundaries while dealing with the problem of reflection and refraction of seismic waves. The present study explores the reflection and refraction phenomena of SH-waves at a corrugated interface between visco-elastic half-space and fibre-reinforced half-space. Method of approximation given by Rayleigh is adopted and the expressions for reflection and transmission coefficients are obtained in closed form for the first and second order approximation of the corrugation. The closed form formulae of these coefficients are presented for a corrugated interface of periodic shape (cosine law interface). It is found that these coefficients depend upon the amplitude of corrugation of the boundary, angle of incidence and frequency of the incident wave. Numerical computations for a particular type of corrugated interface are performed and a number of graphs are plotted. Some special cases are derived.

Frequency-Dependent Spherical-Wave Reflection in Acoustic Media: Analysis and Inversion

Spherical-wave reflectivity (SWR), which describes the seismic wave reflection in real subsurface media more accurately than plane-wave reflectivity (PWR), recently, again attracts geophysicists’ attention. The recent studies mainly focus on the amplitude variation with offset/angle (AVO/AVA) attributes of SWR. For a full understanding of the reflection mechanism of spherical wave, this paper systematically investigates the frequency-dependent characteristics of SWR in a two-layer acoustic medium model with a planar interface. Two methods are used to obtain SWR. The first method is through the calculation of classical Sommerfeld integral. The other is by 3D wave equation numerical modeling. To enhance computation efficiency, we propose to perform wave equation simulation in cylindrical coordinates, wherein we for the first time implement unsplit convolutional perfectly matched layer as the absorbing boundary. Both methods yield the same results, which demonstrate the validity and accuracy of the computation. From both the numerical tests and the theoretical demonstration, we find that the necessary condition when frequency dependence of SWR occurs is that the upper and lower media have different velocities. At the precritical small angle, the SWR exhibits complicated frequency-dependent characteristics for varying medium parameters. Especially when the impedance of upper medium equals that of lower one, the PWR is zero according to geometric seismics. Whereas the SWR is nonzero: the magnitude of SWR decreases with growing frequency, and approaches that of the corresponding PWR at high frequency; the phase of SWR increases with growing frequency, but approaches 90° or −90° at high frequency. At near- and post-critical angles, large difference exists between SWR and PWR, and the difference is particularly great at low frequencies. Finally, we propose a nonlinear inversion method to estimate physical parameters and interface depth of media by utilizing the frequency-dependent SWR at a precritical small angle. Tests show that good inversion results can be obtained when the input data contain both low and moderate frequencies.

THE THREE‐DIMENSIONAL IMAGING TECHNOLOGY AND ITS IMPROVEMENT FOR GEOLOGICAL STRUCTURE BASED ON TRT SYSTEM

AbstractThe TRT technology is used to achieve recognition of the disaster body with the help of seismic wave reflection principle; it can locate disaster body using a confocal ellipsoid changing with time composed by seismic focus and the receiving focus. By comparing the abnormal image area formed by TRT technology with the tunnel disaster area caused by the earthquake, the TRT anomaly area is divided into four types, which is cluster abnormal area, single abnormal area, faulted abnormal area and interbedded abnormal area. Aiming at TRT technology's own problems which is that the calculation of direct wave velocity is not enough accurate and the setting of background wave velocity is unreasonable, a corresponding improvement method is proposed. On one hand, to get the actual direct wave velocity between seismic focus and the receiving focus, through calculating the minimum actual spreading track of the direct wave in the tunnel. On the other hand, to obtain 1‐a confidence interval of actual direct wave velocity in the condition of Gaussian distribution, based on the distribution of direct wave velocity. To entry the upper and lower limits of the confidence interval as the background velocity into the TRT system, and gain two sets TRT's image, which gets rid of the singleness and blindness in setting the background wave velocity, and makes a certain confidence interval consideration for the improved geological hazard forecasting. The result of the present example shows that the effect of improved geological hazard forecasting is much better than the forecasting effect of setting the background wave velocity, in a certain degree, that avoids the possibility of omission in disaster prediction.

Seismic isolation of two dimensional periodic foundations

Phononic crystal is now used to control acoustic waves. When the crystal goes to a larger scale, it is called periodic structure. The band gaps of the periodic structure can be reduced to range from 0.5 Hz to 50 Hz. Therefore, the periodic structure has potential applications in seismic wave reflection. In civil engineering, the periodic structure can be served as the foundation of upper structure. This type of foundation consisting of periodic structure is called periodic foundation. When the frequency of seismic waves falls into the band gaps of the periodic foundation, the seismic wave can be blocked. Field experiments of a scaled two dimensional (2D) periodic foundation with an upper structure were conducted to verify the band gap effects. Test results showed the 2D periodic foundation can effectively reduce the response of the upper structure for excitations with frequencies within the frequency band gaps. When the experimental and the finite element analysis results are compared, they agree well with each other, indicating that 2D periodic foundation is a feasible way of reducing seismic vibrations.

The Fine-Structure Interpretation and Favorable Objective Evaluation of Quanyiduan in Fulongquan Area

According to the needs of exploration and development, the main purpose of the Fulongquan region layer (Quanyiduan) to explain the fine structure and a favorable objective evaluation. Fine structural interpretation based on high-resolution, high fidelity and high signal to noise ratio of seismic data, the use of Landmark Interaction software layer on the purpose well - seismic calibration, determine the target layer of seismic reflection and seismic wave group phase characteristics of other wells in the area of information work carried out under the lateral auxiliary tracking method with variable velocity mapping layers of the structure plan aims to implement the target zone traps. In the structural interpretation based on the use of coherent technology and time slice for fault identification, combined with relevant geological data on the target layer of oil a comprehensive evaluation, selection of a good oil and gas traps, providing for the exploration and development goals.

Ribbed moraines in northern Manitoba, Canada: characteristics and preservation as part of a subglacial bed mosaic near the core regions of ice sheets

Ribbed moraines are enigmatic glacial landforms for which different models, with contrasting paleoglaciologic implications, have been proposed to explain their formation. Despite the great deal of attention this type of landform has received over the last several decades, ribbed moraine fields in northern Manitoba, Canada are among the largest in the world but have been seldom studied. Ribbed moraines in this part of the world overlie the low-relief Canadian Shield, are not constrained by topography, and are part of a spatial subglacial-landform assemblage associated with drumlinoid ridges within palimpsest and relict-type Glacial Terrain Zones. Field observations herein provide new insights into the characteristics of these transverse-to ice-flow ridges at landscape (mapping and spatial analysis) and landform (internal structure using high-resolution shear wave (S-wave) seismic reflection surveys, sedimentological characteristics, clast-fabric analyses) scales. Two main types of ribbed moraine are recognized: ‘pristine’, high amplitude straight-crested ridges and secondarily-modified subdued ‘drumlinized’ ridges. Ribbed moraine in northeast Manitoba consist of massive, matrix-supported till at surface, which is similar in matrix texture and composition to the regional till sheet, though pristine moraines show a higher concentration of boulders. A seismic profile reveals subparallel-to surface layered stratigraphy with only minor folding and no major unconformities (stacking or faulting).The demonstrated fragmentary nature of ribbed moraine fields, the inherited signature of the till within these fields, the secondary patchy drumlinization of the ridges, and the more abundant granitoid outcrops in areas of intense modification all suggest that subglacial ribbed moraine formed from pre-existing sediments and were later preserved and/or partially reworked through a regional mosaic of shifting subglacial bed conditions. We therefore make the case that pristine (unmodified) moraines were preserved beneath stable sticky spots. We support a link between ribbed moraine and widespread cold-based and/or dewatered subglacial conditions in inner-core regions of ice sheets, but for reasons of preservation, and not necessarily formation.

Fault — Dissolution front relations and the Dead Sea sinkhole problem

There are two conflicting models of sinkhole development along the Dead Sea (DS). The first one considers structural control on sinkholes, constraining them to tectonic lineaments. This hypothesis is based on seismic reflection studies suggesting that sinkholes are the surface manifestations of active neotectonic faults that may serve as conduits for under-saturated groundwater, enabling its access across aquiclude layers. Another hypothesis, based on results of multidisciplinary geophysical studies, considers the salt edge dissolution front as the major site of sinkhole formation. This hypothesis associates sinkholes with karstification of the salt edge by deep and shallow undersaturated groundwater. Our recent seismic reflection and surface wave studies suggest that salt formed along the active neotectonic faults. Sinkholes form in a narrow strip (60–100m wide) along a paleo-shoreline constrained by faults and alluvial fans which determined the edge of the salt layer. This scenario reconciles the two major competing frameworks for sinkhole formation.

Seismic characterization of naturally fractured reservoirs using amplitude versus offset and azimuth analysis

ABSTRACTP‐wave seismic reflection data, with variable offset and azimuth, acquired over a fractured reservoir can theoretically be inverted for the effective compliance of the fractures. The total effective compliance of a fractured rock, which is described using second‐ and fourth‐rank fracture tensors, can be represented as background compliance plus additional compliance due to fractures. Assuming monoclinic or orthotropic symmetry (which take into account layering and multiple fracture sets), the components of the effective second‐ and fourth‐rank fracture compliance tensors can be used as attributes related to the characteristics of the fractured medium. Synthetic tests indicate that using a priori knowledge of the properties of the unfractured medium, the inversion can be effective on noisy data, with S/N on the order of 2. Monte Carlo simulation was used to test the effect of uncertainties in the a priori information about elastic properties of unfractured rock. Two cases were considered with Wide Azimuth (WAZ) and Narrow Azimuth (NAZ) reflection data and assuming that the fractures have rotationally invariant shear compliance. The relative errors in determination of the components of the fourth‐rank tensor are substantially larger compared to the second‐rank tensor, under the same assumptions.Elastic properties of background media, consisting in horizontal layers without fractures, do not cause azimuthal changes in the reflection coefficient variation with offset. Thus, due to the different nature of these properties compared to fracture tensor components (which cause azimuthal anomalies), simultaneous inversion for background isotropic properties and fracture tensor components requires additional constraints.Singular value decomposition (SVD) and resolution matrix analysis can be used to predict fracture inversion efficacy before acquiring data. Therefore, they can be used to determine the optimal seismic survey design for inversion of fracture parameters. However, results of synthetic inversion in some cases are not consistent with resolution matrix results and resolution matrix results are reliable only after one can see a consistent and robust behaviour in inversion of synthetics with different noise levels.

Compressional and EM wave velocity anisotropy in a temperate glacier due to basal crevasses, and implications for water content estimation

AbstractWe have conducted a series of experiments designed to investigate elastic and electromagnetic (EM) velocity anisotropy associated with a preferentially aligned fracture system on a temperate valley glacier in south-central Alaska, USA. Measurements include a three-dimensional compressional wave (P-wave) seismic reflection survey conducted over a 300 m x 300 m survey patch, with uniform source grid and static checkerboard receiver pattern. Additionally, we acquired a multi-azimuth, multi-offset, polarimetric ground-penetrating radar (GPR) reflection experiment in a wagon-wheel geometry with 94° of azimuthal coverage. Results show azimuthal variation in the P-wave normal-moveout velocity of >3% (3765 and 3630 m s–1 in the fast and slow directions respectively) and difference of nearly 5% between the fast (0.164 m ns–1) and slow (0.156 m ns–1) EM velocities. Fracture orientations estimated from the GPR and seismic velocity data are consistent and indicate a preferred fracture orientation that is 30-45° oblique to glacier flow; these measurements agree with borehole observations. Anisotropic analysis of the polarimetric data gives a single volumetric water content estimate of 0.73 ±0.11%. We conclude that meaningful estimates of physical properties in glaciers based on EM or seismic velocity measurements require collecting data such that the presence of anisotropy can be evaluated and an anisotropic analysis employed when necessary.

The inverse problem of seismic fault determination using part time measurements

This paper shows how a part time measurement T of the acceleration on the ground can be done to avoid the consideration of reflections of seismic waves on the Moho discontinuity. A bounded hemispherical solid is considered with radius greater than c pT , but smaller than the Moho depth, in order to get the null boundary conditions on the hemispherical surface. The inverse problem to determine the fault plane and the time-dependent fault geometry is well-defined and solved in closed form by the reciprocity gap functional method. Two formulae are established for the components of the fault slip, which involve time and spatial Fourier transforms of some quantities related to the reciprocity gap functional. A forward initial boundary value problem in elastodynamics enables us to get the internal wave field, the shear stress as well as the normal stress on the fault. This full solution would be useful for understanding the friction mechanism on the fault during a real strike, whenever the initial uniform tectonic stresses are known from geophysical considerations.

Influence of magma ascent rate on carbon dioxide degassing at oceanic ridges: Message in a bubble

In order to quantify the magma ascent rate beneath oceanic ridges, we propose a new method based on vesicle size distribution (VSD) and volatiles measurements (CO2 and H2O) on 65 fresh glasses from the global Mid-Ocean Ridge system. Comparisons of VSD between the main oceanic basins reveal that Mid-Ocean-Ridge-Basalts (MORB) from the Pacific Ocean have significantly higher bubble densities (148−124+739 bubbles/cm2) and initial population densities ln(n0)=19.6±2.8cm−4 but lower vesicularities (∼0.1%). We determine the residence time of bubbles in the magma using the linear relationship between the logarithm of the density population and the vesicle diameters. Assuming a constant bubble growth rate (G=1.5×10−7cm/s), we suggest that the transit times of the magmas through the oceanic crust are shorter beneath Pacific ridges (∼2 h) than elsewhere (∼15 h). In addition, the CO2 and H2O contents of the studied glasses allow the carbon saturation pressure to be calculated. Pacific MORB display a significantly lower carbon dioxide saturation pressure (Psat=843−221+300bars) than Atlantic and Indian MORB (Psat=1898−827+1466bars) but identical pressures of eruption (Pe∼310bars). Consequently, the distance traveled by bubbles from the vesiculation depth to the seafloor is shorter for the Pacific (∼1.9km) than for the Atlantic and Indian oceans (∼5.2km): the longer the transit time, the longer the distance traveled. A closer inspection of the data revealed that the decompression rate (dP/dt) varied from 5.0×102 to 2.3×104Pa/s and correlated positively with the measured bubble densities (nb/m3) as expected from experimental data and numerical modeling. At the global scale, most of the Pacific samples are characterized by high ascent rates (0.25−0.13+0.26m/s) relative to those from the Atlantic (0.11−0.06+0.15m/s) and the Indian samples (0.09−0.03+0.05m/s). However, at the local scale some samples from the Mid-Atlantic Ridge at 37 °N (where the reflections of seismic waves from crustal magma chamber have been observed) are not distinguishable from the Pacific data set having high ascent rates and large bubble densities. We suggest that the method presented in this study could be used to identify spots along the Mid-Oceanic-Ridge system where magma chambers are possibly present.

Applying accurate gradients of seismic wave reflection coefficients (SWRC) to the inversion of seismic wave velocities

Through solving the Zoeppritz’s partial derivative equations, we have obtained accurate partial derivatives of reflected coefficients of seismic wave with respect to P- and S-wave velocities. With those partial derivatives, a multi-angle inversion is developed for seismic wave velocities. Numerical examples of different formation models show that if the number of iterations goes over 10, the relative error of inversion results is less than 1%, whether or not there is interference among the reflection waves. When we only have the reflected seismograms of P-wave, and only invert for velocities of P-wave, the multi-angle inversion is able to obtain a high computation precision. When we have the reflected seismograms of both P-wave and VS-wave, and simultaneously invert for the velocities of P-wave and VS-wave, the computation precisions of VS-wave velocities improves gradually with the increase of the number of angles, but the computation precision of P-wave velocities becomes worse. No matter whether the reflected seismic waves from the different reflection interface are coherent or non-coherent, this method is able to achieve a higher computation precision. Because it is based on the accurate solution of the gradient of SWRCs without any additional restriction, the multi-angle inversion method can be applied to seismic inversion of total angles. By removing the difficulties caused by simplified Zoeppritz formulas that the conventional AVO technology struggles with, the multi-angle inversion method extended the application range of AVO technology and improved the computation precision and speed of inversion of seismic wave velocities.

Characterization of Intrabasin Faulting and Deformation for Earthquake Hazards in Southern Utah Valley, Utah, from High-Resolution Seismic Imaging

We conducted active and passive seismic imaging investigations along a 5.6‐km‐long, east–west transect ending at the mapped trace of the Wasatch fault in southern Utah Valley. Using two‐dimensional (2D) P ‐wave seismic reflection data, we imaged basin deformation and faulting to a depth of 1.4 km and developed a detailed interval velocity model for prestack depth migration and 2D ground‐motion simulations. Passive‐source microtremor data acquired at two sites along the seismic reflection transect resolve S ‐wave velocities of approximately 200 m/s at the surface to about 900 m/s at 160 m depth and confirm a substantial thickening of low‐velocity material westward into the valley. From the P ‐wave reflection profile, we interpret shallow (100–600 m) bedrock deformation extending from the surface trace of the Wasatch fault to roughly 1.5 km west into the valley. The bedrock deformation is caused by multiple interpreted fault splays displacing fault blocks downward to the west of the range front. Further west in the valley, the P ‐wave data reveal subhorizontal horizons from approximately 90 to 900 m depth that vary in thickness and whose dip increases with depth eastward toward the Wasatch fault. Another inferred fault about 4 km west of the mapped Wasatch fault displaces horizons within the valley to as shallow as 100 m depth. The overall deformational pattern imaged in our data is consistent with the Wasatch fault migrating eastward through time and with the abandonment of earlier synextensional faults, as part of the evolution of an inferred 20‐km‐wide half‐graben structure within Utah Valley. Finite‐difference 2D modeling suggests the imaged subsurface basin geometry can cause fourfold variation in peak ground velocity over distances of 300 m.

The Goos-Hänchen shift of wide-angle seismic reflection wave

The partial derivative equations of Zoeppritz equations are established and the derivatives of each matrix entry with respect to wave vectors are derived in this paper. By solving the partial derivative equations we obtained the partial derivatives of seismic wave reflection coefficients with respect to wave vectors, and computed the Goos-Hanchen shift for reflected P- and VS-waves. By plotting the curves of Goos-Hanchen shift, we gained some new insight into the lateral shift of seismic reflection wave. The lateral shifts are very large for glancing wave or the wave of the incidence angle near the critical angle, meaning that the seismic wave propagates a long distance along the reflection interface before returning to the first medium. For the reflection waves of incidence angles away from the critical angle, the lateral shift is in the same order of magnitude as the wavelength. The lateral shift varies significantly with different reflection interfaces. For example, the reflected P-wave has a negative shift at the reflection interface between mudstone and sandstone. The reflected VS-wave has a large lateral shift at or near the critical angle. The lateral shift of the reflected VS-wave tends to be zero when the incidence angle approaches 90°. These observations suggest that Goos-Hanchen effect has a great influence on the reflection wave of wide-angles. The correction for the error caused by Goos-Hanchen effect, therefore, should be made before seismic data processing, such as the depth migration and the normal-moveout correction. With the theoretical foundation established in this paper, we can further study the correction of Goos-Hanchen effect for the reflection wave of large incidence angle.

Long-offset AVO inversion of PP reflections from plane interfaces using effective reflection coefficients

A conventional amplitude variation with offset (AVO) inversion is based on geometrical seismics which exploit plane-wave reflection coefficients to describe the reflection phenomenon. Widely exploited linearizations of plane-wave coefficients are mostly valid at pre-critical offsets for media with almost flat and weak-contrast interfaces. Existing linearizations do not account for the seismic frequency range by ignoring the frequency content of the wavelet, which is a strong assumption. Plane-wave reflection coefficients do not fully describe the reflection of seismic waves at near-critical and post-critical offsets, because reflected seismic waves are typically generated by point sources. We propose an improved approach to AVO inversion, which is based on effective reflection coefficients (ERCs). ERCs generalize plane-wave coefficients for seismic waves generated by point sources and therefore more accurately describe near-critical and post-critical reflections where head waves are generated. Moreover, they are frequency-dependent and incorporate the local curvatures of the wavefront and the reflecting interface. In our study, we neglect the effect of interface curvature and demonstrate the advantages of our approach on synthetic data for a simple model with a plane interface separating two isotropic half-spaces. A comparison of the inversion results obtained with our approach and the results from an AVO inversion method based on the exact plane-wave reflection coefficient suggests that our method is superior, in particular for long-offset ranges which extend to and beyond the critical angle. We thus propose that long offsets can be successfully exploited in an AVO inversion under the correct assumption about the reflection coefficient. Such long-offset AVO inversion shows the potential of outperforming a conventional moderate-offset AVO inversion in the accuracy of estimated model parameters.

An Accurate Method of Computing the Gradient of Seismic Wave Reflection Coefficients (SWRCs) for the Inversion of Stratum Parameters

The optimization inversion method based on derivatives is an important inversion technique in seismic data processing, where the key problem is how to compute the Jacobian matrix. The computational precision of the Jacobian matrix directly influences the success of the optimization inversion method. Currently, most of the AVO (amplitude versus offset) inversions are based on approximate expressions for the Zoeppritz equations to obtain the derivatives of the seismic wave reflection coefficients (SWRCs) with respect to the stratum parameters. As a result, the computational precision and range of applications of these AVO inversions are restricted undesirably. In order to improve the computational precision and to extend the range of applications of AVO inversions, the partial derivative equations of the Zoeppritz equations are established, with respect to the ratios of wave velocities and medium densities. By solving the partial derivative equations of the Zoeppritz equations accurately, we obtained the partial derivative of SWRCs with respect to the ratios of seismic wave velocities and medium densities. With the help of the chain rule for derivatives, the gradient of the SWRCs can be accurately computed. To better understand the behavior of the gradient of the SWRCs, we plotted the partial derivative curves of the SWRCs, analyzed the characteristics of these curves, and gained some new insight into the derivatives. Because only a linear system of equations is solved in our method without adding any new restrictions, the new computational method has both high precision and a quick running speed; it is not only suitable for small incident angles and weak reflection seismic waves but also for large incident angles and strong reflection seismic waves. With the theoretical foundations established in the article, we can further study inversion problems for layered stratum structures and we can further improve the computational speed and precision of the inversions.

Survey and Analysis of the Regularity of the Surface Crack in the Loess Tunnel of the Special Passenger Line

We have done a survey about the surface crack of the loess tunnel of Zheng-xi passenger railway by field survey, geophysical exploration test and pit detection and also have researched the produced regularity of the surface crack of the loess tunnel, especially about in the depth. The result of the survey and the detection indicates that: (1)The surface crack is mostly visible in the shallow area of the loess tunnel entrance. The visible width of the surface is extensive (0.2~200mm) and it is mostly visible in the tunnel, the depth of which is below 60m. The visible or wide cracks mostly appear in the area whose surface settlement is above 80mm. The width of the surface crack of the tunnel, which has a more shallow depth and a larger settlement, is much wider. (2)The effect of the High-density electrical method reflecting the development of the surface crack is obvious. The method of seismic reflection wave and seismic imaging is more accurate than Rayleigh wave in interpreting depth development of the crack. (3)There are two kinds of performance of the surface crack: longitudinal crack that inclines to the inside on both side of the tunnel and circumferential crack perpendicular to the axis of the tunnel. (4)The visible crack depth of the surface crack is limited, which is about 3.0~10m and it always doesn't reach the top of the tunnel. The depth by the geophysical exploration test is much more depth, which is about 10~15m.