Seismic Earth Research Articles

Various far-field hydrological responses during 2015 Gorkha earthquake at two distant wells

Aquifer hydraulic parameter can change during earthquakes. Continuous monitoring of the response of water level to seismic waves or solid Earth tides provides an opportunity to document how earthquakes influence hydrological properties. Here, we use data of two groundwater wells, Dian-22 (D22) and Lijiang (LJ) well, in southeast Tibet Plateau in response to the 2015 Mw 7.8 Gorkha earthquake to illustrate hydrological implications. The coherences of water level and seismic wave before and after the far-field earthquake show systematic variations, which may confirm the coseismic dynamic shaking influence at high frequencies (f > 8 cpd). The tidal response of water levels in these wells shows abrupt coseismic changes of both phase shift and amplitude ratio after the earthquake, which may be interpreted as an occurrence in the vertical permeability of a switched semiconfined aquifer in the D22 well, or an enhancement unconfined aquifer in the LJ well. Using the continuous short-term transmissivity monitoring, we show that the possible coseismic response for about 10 days and instant healing after 10 days to the causal earthquake impact. Thus, the dynamic shaking during the Gorkha earthquake may have caused the short-term aquifer responses by reopening of preexisting vertical fractures and later healing at epicentral distances about 1500 km.

A Pseudodynamic Approach of Seismic Active Pressure on Retaining Walls Based on a Curved Rupture Surface

Reasonable determination of the magnitude and distribution of dynamic earth pressure is one of the major challenges in the seismic design of retaining walls. Based on the principles of pseudodynamic method, the present study assumed that the critical rupture surface of backfill soil was a composite curved surface which was in combination with a logarithmic spiral and straight line. The equations for the calculation of seismic total active thrusts on retaining walls were derived using limit equilibrium theory, and earth pressure distribution was obtained by differentiating total active thrusts. The effects of initial phase, amplification factor, and soil friction angle on the distribution of seismic active earth pressure have also been discussed. Compared to pseudostatic and pseudodynamic methods for the determination of planar failure surface forms, the proposed method receives a bit lower value of seismic active earth pressures.

Seismic sources and Earth structure in the transition zone between Fore-Balkan unit and Moesian platform, NE Bulgaria

Investigations of hydraulically induced micro-seismicity are typically connected with magma injections, exploitation of geothermal fields and salt mines. Our study examines the seismicity and seismic sources in a peri-platform region with long salt production history. In addition, a very large site for extraction of aggregates and limestone is presented in the area. Increased seismicity in the region has been observed for several decades as during the study period of the last 12 years, more than 1000 events with magnitude $$M < 4.3$$ have been registered. To study the complex seismic sources concentrated in such small area spatial distribution of seismicity and fault plane solutions are analyzed together with available geological and geophysical data, in order to connect registered earthquakes swarms with geological structures. Results show that several faults are outlined from geological information and confirmed by interpretation of geophysical data. Very different focal mechanisms calculated for the 13 earthquakes in the near region of the salt production site cannot propose a dominant fault mechanism and confirm the complexity of the seismic sources in the area. Our results suppose that activation of some of these structures is more likely due to water injected in the salt dome as part of the production process, which changes the stress equilibrium in the Earth crust.

Upper Bound of Seismic Active Earth Pressure on Gravity Retaining Wall with Limited Backfill Width

The failure mechanisms of backfill with limited width that is subjected to a co-application of earthquake force and surcharge formed by single and double wedges, respectively, were introduced to address the active earth pressure acting on gravity walls. An analytic model that is applicable to general cases of tilt walls with frictional backs and inclined ground surfaces was established by incorporating the quasi-static Mononobe-Okabe method and upper bound limit analysis. The reasonability and effectiveness of this technique were verified and supported by a comparison with results from reported laboratory model tests. A sample case analysis revealed a nonlinear distribution of active earth pressure on a gravity wall with limited backfill width. Coulomb's solution and three other published methods tended to overestimate the earth pressure measured in the laboratory more significantly than the proposed method did when the width of the backfill was reduced to a critical threshold. The superiority of this suggested technique increased with the shrinkage of backfill width. Moreover, the ascending horizon seismic coefficient k and surcharge q mobilized an increasing active thrust on the wall while easing and enlarging the crack angle of the slip surface, respectively.

Evaluation of Seismic Behavior and Earth’s Surface Acceleration, by Interaction of Tunnels with Different Shapes and Different Types of Soils

With the increasing population and the consequent needs for transport facilities, the construction of tunnels in urban environments is fast growing. Tunneling at each depth of the soil, causes changes in the earth’s surface; this is more important about urban areas tunnels, especially when crossing the residential areas, so having knowledge of their performance is really important. Some of the consequences of underground tunneling are earth surface moving around the tunnel, movement of tunnel’s surrounding and changes in earthquake acceleration. The performance and behavior of underground structures have been studied by numerous researchers, but the effect of tunneling on earthquake records and its effects on aboveground structures have been getting less attention. The current article will try to study and examine the changes in seismic velocity at ground level, structural response spectrum, and Fourier spectrum with digging a circular tunnel. The results show that digging a circular tunnel at ground level will cause a change in the earthquake records profile.

Reply to discussion of “Pseudodynamic approach for computation of seismic passive earth resistance including seepage” by Syed Mohd Ahmad [Ocean Engineering 63 (2013) 63–71

Reply to discussion of “Pseudodynamic approach for computation of seismic passive earth resistance including seepage” by Syed Mohd Ahmad [Ocean Engineering 63 (2013) 63–71

Pseudo-static passive response of retaining wall supporting Φ backfill

In this paper, an analytical expression of seismic passive earth pressure acting on battered-face rigid retaining wall is derived using Horizontal Slices Method and limit equilibrium principles. The solution of this problem generates a non-linear failure surface. The results are presented in tabular form and a detailed parametric study has been made for the variation of seismic passive earth pressure coefficient by plotting graphs with a wide range of variation of parameters such as angle of internal friction (Φ), angle of wall friction (δ), wall inclination angle (α), horizontal and vertical seismic coefficients (kh and kv), and surcharge loading (q).

Discussion on “Pseudodynamic approach for computation of seismic passive earth resistance including seepage” by Syed Mohd Ahmad [Ocean Engineering 63 (2013) 63–71

Discussion on “Pseudodynamic approach for computation of seismic passive earth resistance including seepage” by Syed Mohd Ahmad [Ocean Engineering 63 (2013) 63–71

Pseudo-dynamic methods for seismic passive earth pressure behind a cantilever retaining wall with inclined backfill

The designing of retaining walls requires the complete knowledge of earth pressure distribution. Under earthquake conditions the design needs special attention to reduce the devastating effect, but under seismic conditions, the available literature mostly uses the pseudo-static analytical solution as an approximate to the real dynamic nature of the complex problem. This paper shows a detailed study on the seismic passive earth thrust behind a cantilever retaining wall with inclined backfill surface by pseudo-dynamic analysis. A planar failure surface has been considered. The effect of variation of parameters such as soil friction angle, wall friction angle and back fill inclination have been explored. A complete analysis shows that the time dependent non-linear behaviour of the pressure distribution obtained in the present method results in more realistic design values of earth pressures under earthquake conditions. Results are provided in tabular and graphical non-dimensional form and compared thoroughly with the existing values in the literature.

Analysis of Seismic Active Earth Pressure on Retaining Walls Based on Pseudo-dynamic Method

AbstractTo examine the seismic active pressure on retaining walls, the pseudo-dynamic method is adopted in deducing the formulas of seismic active earth pressure. The critical rupture angle is analytically solved on the basis of conventional sliding wedge limit equilibrium theory. The influencing factors considered for the formulas are seismic force, surcharge angle, the internal friction angle and cohesion of the backfill for retaining walls, the friction angle and cohesion between retaining walls and backfill, and the inclination of retaining walls. The effects of these factors on critical failure angle and seismic active earth pressure coefficient are analyzed. Results show that the critical rupture angle is less than that is calculated using the Mononobe-Okabe method, in which the soil amplification factor and cohesion of backfill are disregarded. The critical rupture angle decreases with increasing soil amplification factor. The seismic active earth pressure coefficient increases with rising seismic ...

Computations of Seismic Passive Resistance and Uplift Capacity of Horizontal Strip Anchors in Sand

In this paper, the limit equilibrium method is used to compute seismic passive earth pressure coefficients and the vertical uplift capacity of horizontal strip anchors in presence of both horizontal and vertical pseudo-static earthquake forces. By considering a simple planar failure surface, distribution of soil reaction is obtained through the use of Kotter’s equation. Presence of pseudo-static seismic forces induces a considerable reduction in the seismic passive earth pressure coefficients. The reduction in seismic passive earth pressure coefficients increases with increase in magnitude of the earthquake accelerations in both horizontal and vertical directions and with increase in wall friction angle. The vertical uplift capacity of horizontal strip anchor is obtained for various values of soil friction angle, embedment ratio and seismic acceleration coefficients in both horizontal and vertical directions by using rigorous computational optimization. Proper justification for selected value of wall friction angle is established. Results are presented in the form of non-dimensional breakout factor for anchor. A significant reduction in breakout factor is observed in presence of both the seismic acceleration coefficients whereas breakout factor increases with increase in soil friction angle and embedment ratio even under the seismic condition. Angles of failure planes keep changing with change in seismic acceleration coefficients and failure zone shifts towards the critical direction of seismic acceleration coefficients. Present results are compared and found in good agreement with some specific available results in literature.

An analytical expression for the seismic passive earth pressure from the c-Φ soil backfills on rigid retaining walls with wall friction and adhesion

An analytical expression for the total seismic passive earth pressure from the c-Φ soil backfills on rigid retaining walls subjected to surcharge and seismic loads is derived considering wall friction and adhesion. The derivation also presents an explicit expression for the critical inclination to the horizontal of the failure plane within the backfill. The developed expressions are analyzed for special cases; the resulting expressions are found to be identical to those presented by earlier researchers for both static and seismic passive earth pressure conditions.

Formulation of Seismic Passive Resistance of Retaining Wall Backfilled with c-F Soil

Knowledge of passive resistance is extremely important and it is the basic data required for the design of geotechnical structures like the retaining wall moving towards the backfill, the foundations, the anchors etc. An attempt is made to develop a formulation for the evolution of seismic passive resistance of a retaining wall supporting c-F backfill using pseudo-static method. Considering a planar rupture surface, the formulation is developed in such a way so that a single critical wedge surface is generated. The variation of seismic passive earth pressure coefficient are studied for wide range of variation of parameters like angle of internal friction, angle of wall friction, cohesion, adhesion, surcharge, unit weight of the backfill material, height and seismic coefficients.

Pseudo-dynamic evaluation of passive response on the back of a retaining wall supporting c-Φ backfill

The study presents a rational analytical approach to obtain the seismic passive response of an inclined retaining wall backfilled with horizontal c-Φ soil. Pseudo-dynamic analysis is carried out to obtain the seismic passive response. Here in this analysis, the critical wedge angle is a single one irrespective of weight, surcharge and cohesion and this fact satisfies the field situation in a more realistic manner. A planer failure surface is considered in the analysis. The effect of soil and wall friction angle, wall inclination, horizontal and vertical earthquake acceleration on the passive resistance and the variation of passive earth pressure along the height of the wall have been explored. A comparison to pseudo-static and other available methods have been made to highlight the non-linearity of seismic passive earth pressure distribution.

Kinematic time migration and demigration of reflections in pre-stack seismic data

SUMMARY In kinematic time migration one maps the time, slope and curvature characteristics of seismic reflection events, referred to as reflection-time parameters, from the recording domain of the seismic data to the time-migration domain. The inverse process is kinematic time demigration. We generalize kinematic time migration and demigration in several respects: the reflection-time parameters may belong to arbitrary source–receiver offsets; local heterogeneity of the time-migration velocity model is accounted for; the mapping operations do not depend specifically on the type of diffraction-time function and the parametrization of the velocity model. Time-migration and time-demigration spreading matrices are obtained as byproducts of the mapping operations. These matrices yield a paraxial expression for the connection between midpoint and image-point gather locations of mapped reflection events. Also, we obtain the time-migration counterpart of the so-called second duality theorem in Kirchhoff depth migration. Diffractions and reflections are assumed to be without conversion, and sources and receivers are located along the same measurement surface. Our framework enables the identification of a full set of first- and second-order reflection-time parameters from time-migrated seismic data followed by a kinematic demigration to the recording domain. The idea of this route is to ‘undo’ eventual errors introduced by time migration and result in reliable estimation of recording-domain invariants, that is, parameters insensitive to the time-migration velocity model. The developed concepts associated with time migration are of interest in reflection seismic and global earth applications. Two numerical examples demonstrate the potential of kinematic time migration and demigration techniques in seismic time imaging and velocity-model building.

Seismic Passive Earth Pressure with Seepage for Cohesionless Soil

The authors deal with the computing seismic passive earth pressure acting on a vertical rigid wall. The wall is provided with a drainage system along soil-structure interface and retains the cohesionless backfill subjected to water seepage. A general solution for the seismic passive earth pressure is presented. The solution is based on Coulomb's theory wherein seismic forces are assumed to be pseudostatic. The solution considers the pore water pressures induced by water seepage and earthquake shaking. Some important parameters are included in the solution. The parameters are the soil effective internal friction angle, wall friction, soil unit weight, and horizontal and vertical seismic acceleration coefficients. The comparison of the total seismic passive earth pressure in horizontal direction from the present method with published works indicates that the present method may be reasonable. The variations of the passive earth pressure coefficient with the soil effective internal friction angle are investigated for different wall friction angles and seismic forces. The effect of the water seepage on the seismic passive earth pressure is also investigated.

Discussion of “Effects of Strain Localization on Seismic Active Earth Pressures” by Jian-Min Zhang, Fei Song, and De-Ji Li

Discussion of “Effects of Strain Localization on Seismic Active Earth Pressures” by Jian-Min Zhang, Fei Song, and De-Ji Li

Closure to “Effects of Strain Localization on Seismic Active Earth Pressures” by Jian-Min Zhang, Fei Song, and De-Ji Li

Closure to “Effects of Strain Localization on Seismic Active Earth Pressures” by Jian-Min Zhang, Fei Song, and De-Ji Li

The Research of Seismic Active Earth Pressure with Mode of Translation by Horizontal Slices Analysis Method and Shaking Table Tests

In order to get the seismic active earth pressure with the mode of translation, adopting some related assumptions of the M-O theory, this paper establishes the first-order differential equation of the Seismic active earth pressure by horizontal slices analysis method and gets the solution of the seismic active earth pressure by boundary conditions. This formula can solve the distribution of the seismic active earth pressure is nonlinear along the wall, the point of application of the dynamic active thrust which is the advantage of this formula and announces the decreasing process of the filling’s rupture angle with the increase of the horizontal peak ground acceleration (PGA) , as well. The rationality and validity of the formula is confirmed by the comparison between the results of the shaking table tests and the formula, respectively. If the retaining wall takes place the mode of translation, the point of application of the seismic active thrust ranges between 0.4 and 0.5 times wall’s height at the horizontal seismic peak ground acceleration (PGA)&lt;0.4g.At the same time, the computational accuracy of the dynamic active thrust, their points of application and the angle of rupture increases with the increase of the horizontal peak ground acceleration at the horizontal PGA&lt;1.0g, as the astigmatic of the retaining wall in highly seismic intensity region supplying the valuable reference.

Pseudo-Dynamic Evolution of Seismic Passive Earth Force and Pressure Behind Retaining Wall

This paper presents a detailed study on the seismic passive earth pressure behind a non-vertical cantilever retaining wall supporting inclined backfill, using pseudo-dynamic method. In addition to the consideration of wall and backfill surface inclination, the soil friction angle, wall friction angle, and both horizontal and vertical seismic coefficients are taken into account. From the obtained results, a non-linear variation of passive earth pressure along the height of the wall is observed. The results compare well with the existing values in research.