Earthquake-induced displacements of gravity retaining walls and anchor-reinforced slopes

This paper examines in terms of seismic performance, the effectiveness of anchor reinforcement against gravity retaining walls used to stabilize a dry homogenous fill slope in earthquake-prone environment. Both analyzed stabilizing measures have the same design yield acceleration estimated from a limit equilibrium approach. The earthquake-induced displacements are calculated using a sliding block formulation of the equation of motion. Sliding failure along the base of the gravity retaining wall and rotational failure of the soil active wedge behind the wall, as well as rotational failure of the slide mass of the anchor-reinforced slope were considered in the present formulation. For the specific characteristics of the analyzed fill slope and input horizontal ground motion, the slope reinforced with anchors appears to experience vertical and horizontal seismic displacements at slope crest smaller by 12% and respectively, 32% than the vertical and horizontal earthquake-induced deformations estimated at the top of the active wedge behind the gravity retaining wall.     

The El Salvador earthquakes of January and February 2001: context, characteristics and implications for seismic risk

The small Central American republic of El Salvador has experienced, on average, one destructive earthquake per decade during the last hundred years. The latest events occurred on 13 January and 13 February 2001, with magnitudes M_w 7.7 and 6.6, respectively. The two events, which were of different tectonic origin, follow the patterns of the seismicity of the region although neither event has a known precedent in the earthquake catalogue in terms of size and location. The earthquakes caused damage to thousands of traditionally built houses and triggered hundreds of landslides, which were the main causes of fatalities. The earthquakes have clearly demonstrated trends of increasing seismic risk in El Salvador due to rapid population expansion in areas of high shaking and landslide hazard, exacerbated by deforestation and uncontrolled urbanisation. The institutional mechanisms required for the control of land use and building practice are very weak and present a major obstacle to risk mitigation.     

地震作用下宝成铁路地质灾害调查分析

2008年5月12日四川汶川发生8.0级特大地震,受此影响宝成铁路成都局管段沿线产生严重的次生地质灾害。通过对铁路沿线震后地质灾害的现场调查,总结了地震作用下产生的灾害类型,分析了地震的致灾作用和地震次生灾害的影响因素,在此基础上结合实际提出防灾工程建议。     

Creep processes in landslides

Displacement of landslide blocks after initial slope failure can be very slow. In most cases movement of the blocks is attributed to sliding along a well-defined slip surface. It is discussed here whether, in addition to these so-called plastic movements, (continuous) creep processes are involved in the slow displacement. The study was carried out in the downstream part of the Bonne valley in the French Alps, where landslide complexes have developed in varved clay material. Displacements of landslide blocks were measured during a period of three years. Inclinometer measurements in flexible tubes showed that a creep zone developed above the slip surface in a zone about 1 m thick. These field observations on creep processes were supported by soil mechanical analysis. Threshold values for creep found in the laboratory nearly coincide with threshold values calculated from a field creep model developed by Ter-Stepanian. During the measuring period ±15 per cent of the displacement of the blocks possibly occurred via continuous creep.     

Tectonic causes of landslides

The relationship between mass movements and tectonic lineaments is investigated in the Pliocene sand and clay terrains of Montepulciano (central Italy). Satellite images and aerial photographs show six families of lineament in southern Tuscany, all of which are present in the Montepulciano area. The orientation, location and density of these are related to corresponding attributes of morphological phenomena such as retrogressive slumps, drainage density and slope angle. Rose diagrams, stereographic plots and statistical analysis all reveal a close correspondence between slumping mass movements and the directions and spatial concentrations of fracture traces. Although slopes and valley trends respond more closely to Apennine (NW-trending) and anti-Apennine (NE-trending) lineaments, the longitudinal axes of landslides are strongly orientated NNW to N, the direction of one of the most significant lineament groups in western central Italy and the local study area.     

Dynamic responses of coastal structures during earthquakes including sediment–sea–structure interaction

The effects of the interaction among sea water, sediment, backfill-soil and coastal structures (embankments) were included in the present study. The formulation is derived from fundamental theories in various fields, including marine hydrodynamics, flow in porous medium, and structural dynamics. The hybrid finite-difference and finite element methods were used in the analysis. The finite-difference method was used to calculate the nonlinear hydrodynamic pressures of sea water as well as the pore water in the sediment acting on the coastal embankment faces by seismic-wave actions. The fluid-filled solid mixture was used to model sediment and back-fill soil and the corresponding dynamic responses were also evaluated by finite difference method. The dynamic response of the coastal structures was calculated by finite element method. The numerical results are presented for various water depths and ground motion intensities. The significant dynamic forces on coastal structures were calculated during earthquakes and the possible sliding of the coastal embankment will occur and the special foundation treatment should be made.     

Earthquake damage detection in the Imperial County Services Building I: The data and time–frequency analysis

The former Imperial County Services Building was a six-story reinforced concrete structure in the El Centro, California, severely damaged by the 1979 Imperial Valley earthquake. It represents a rare case of an instrumented building that has been damaged, and thus can serve as a full-scale benchmark to evaluate and further develop structural health monitoring methods. This paper presents an analysis of inter-story drifts, and of changes in the first NS and EW system frequencies (estimated from the ridge of the Gabor transform of the relative roof displacement response) as indicators of the occurrence of damage. The detected initial decreases of system frequency, of about 28% for NS and 24% for EW motions, are not believed to be due to severe damage. The subsequent decreases, of about 44% for NS and 21% for EW motions, are attributed to damage. Near the end of shaking, increases of about 35% for the NS and 36% for EW motions were detected. (These percentage changes were computed with respect to the previous value for particular interval, rather than a fixed reference). During the most severe shaking, the inter-story drifts exceeded 0.5% for NS and 1.5% for EW motions.     

Source parameters and scaling relationships in the Friuli-Venezia Giulia (Northeastern Italy) region

We estimated the source parameters of 53 local earthquakes (2.0<M_L<5.7) of the Friuli-Venezia Giulia (Northeastern Italy) area, recorded by the short-period local seismic network of the Istituto Nazionale di Oceanografia e Geofisica Sperimentale (OGS), in the period 1995-2003. Data were selected on the basis of high quality locations and focal mechanisms. Standard H/V spectral ratios (HVRS) of the three-component stations of the network were performed in order to assess local amplifications, and only stations showing HVRS not exceeding two were considered for the source parameters estimation. Both velocity and acceleration data were used to compute the SH-wave spectra. Observed spectra were corrected for attenuation effects using an independent regional estimate of the quality factor Q and a station dependent estimate of the spectral decay parameter k. Only earthquakes with M_L>3.0 recorded with a sampling rate of 125 cps were used to compute k, thus allowing to visualize a linear trend of the high frequency acceleration spectrum up to 40-50 Hz. SH-wave spectra, corrected for attenuation, showed an ω⁻² shape allowing a good fit with the Brune model. Seismic moments and Brune radii ranged between 1.5×10¹² and 1.1×10¹⁷  N m and between 0.1 and 2.7 km respectively. We obtained M_o=1.1×10¹⁷  N m for the seismic moment of the Kobarid (SLO) main shock, in good agreement with the Harvard CMT solution (M_o=3.5×10¹⁷  N m). Brune stress drops were confined to the range from 0.07 to 5.31 MPa, with an average value of 0.73 MPa and seem to be approximately constant over five orders of magnitude of seismic moment. Radiated seismic energy computed from two nearby stations scales with seismic moment according to , and apparent stress values are between 0.02 and 4.26 MPa. The observed scatter of Brune stress drop data allowed to hypothesize a scaling relation between seismic moment and corner frequency in order to accommodate both Brune stress drop and apparent stress scalings. No systematic differences are evidenced between stress parameters of earthquakes with different focal mechanisms. As a consequence, a relation of the seismic stress release with the strength of rocks can be hypothesized. A high correlation (r>0.9) of Brune stress drop is found with both apparent stress and RMS stress drop, according to and respectively.     

The droughts of 1996–1997 and 2004–2005 in Amazonia: hydrological response in the river main‐stem

Severe hydrological droughts in the Amazon have generally been associated with strong El Niño events. More than 100 years of stage record at Manaus harbour confirms that minimum water levels generally coincide with intense warming in the tropical Pacific sea waters. During 2005, however, the Amazon experienced a severe drought which was not associated with an El Niño event. Unless what usually occurs during strong El Niño events, when negative rainfall anomalies usually affect central and eastern Amazon drainage basin; rainfall deficiencies in the drought of 2005 were spatially constrained to the west and southwest of the basin. In spite of this, discharge stations at the main‐stem recorded minimum water levels as low as those observed during the basin‐wide 1996–1997 El Niño‐related drought. The analysis of river discharges along the main‐stem and major tributaries during the drought of 2004–2005 revealed that the recession on major tributaries began almost simultaneously. This was not the case in the 1996–1997 drought, when above‐normal contribution of some tributaries for a short period during high water was crucial to partially counterbalance high discharge deficits of the other tributaries. Since time‐lagged contributions of major tributaries are fundamental to damp the extremes in the main‐stem, an almost coincident recession in almost all tributaries caused a rapid decrease in water discharges during the 2005 event. Copyright © 2010 John Wiley & Sons, Ltd.     

Moment-tensor solutions estimated using optimal filter theory: global seismicity, 2001

Moment-tensor solutions, estimated using optimal filter theory, are listed for 290 moderate-to-large size earthquakes that occurred during 2001.     

临汾市地震台网网内地震震级与山西省地震台网的对比研究

选取2012年3月1日至12月31日临汾市地震台网记录到的ML1.0以上地震,对每个地震进行重新定位,并与山西地震台网的定位结果进行对比分析,找到两台网所定震级的偏差系数,用以修正临汾台网的震级,提高测定结果的精度。     

Influence of fluids and magma on earthquakes: seismological evidence

In this paper, we present seismological evidence for the influence of fluids and magma on the generation of large earthquakes in the crust and the subducting oceanic slabs under the Japan Islands. The relationship between seismic tomography and large crustal earthquakes (M=5.7-8.0) in Japan during a period of 116 years from 1885 to 2000 is investigated and it is found that most of the large crustal earthquakes occurred in or around the areas of low seismic velocity. The low-velocity zones represent weak sections of the seismogenic crust. The crustal weakening is closely related to the subduction process in this region. Along the volcanic front and in back-arc areas, the crustal weakening is caused by active volcanoes and arc magma resulting from the convective circulation process in the mantle wedge and dehydration reactions in the subducting slab. In the forearc region of southwest Japan, fluids are suggested in the 1995 Kobe earthquake source zone, which have contributed to the rupture nucleation. The fluids originate from the dehydration of the subducting Philippine Sea slab. The recent 2001 Geiyo earthquake (M=6.8) occurred at 50 km depth within the subducting Philippine Sea slab, and it was also related to the slab dehydration process. A detailed 3D velocity structure is determined for the northeast Japan forearc region using data from 598 earthquakes that occurred under the Pacific Ocean with hypocenters well located with SP depth phases. The results show that strong lateral heterogeneities exist along the slab boundary, which represent asperities and results of slab dehydration and affect the degree and extent of the interplate seismic coupling. These results indicate that large earthquakes do not strike anywhere, but only anomalous areas which can be detected with geophysical methods. The generation of a large earthquake is not a pure mechanical process, but is closely related to physical and chemical properties of materials in the crust and upper mantle, such as magma, fluids, etc.     

Centroid-moment tensor solutions for 113 large earthquakes in 1977–1980

The Centroid-Moment Tensor technique is applied to 113 large earthquakes of the period 1977–1980, including all the shallow events with magnitude m_b, M_s or M_L 6.5. We use digital data recorded by the Global Digital Seismograph Network (GDSN) and International Deployment of Accelerometers (IDA) networks. Solutions are determined for three sequences of events close in time by inverting mantle wave data simultaneously for multiple sources.     

Seismic hazard assessment of Western Coastal Province of Saudi Arabia:deterministic approach

Seismic hazard assessment is carried out by utilizing deterministic approach to evaluate the maximum expected earthquake ground motions along the Western Coastal Province of Saudi Arabia. The analysis is accomplished by incorporating seismotectonic source model,determination of earthquake magnitude(Mmax), set of appropriate ground motion predictive equations(GMPE), and logic tree sequence. The logic tree sequence is built up to assign weight to ground motion scaling relationships. Contour maps of ground acceleration are generated at different spectral periods. These maps show that the largest ground motion values are emerged in northern and southern regions of the western coastal province in Saudi Arabia in comparison with the central region.     

1980–1990: Ten years of geochemical investigation at Phlegrean Fields (Italy)

A systematic geochemical investigation on the thermal manifestations of the volcanic area of Phlegrean Fields started in 1980, with the aim of obtaining useful information about the changes possibly occurring at the same time of vertical ground movements, termed as “bradyseismic”, which frequently interested this area.The attention was initially given to the fumaroles and the boiling pools of Solfatara and Pisciarelli, then subsequently extended to thermal springs, dug wells, and crater lakes.Analytical data pertaining to a period preceding the last crisis of 1982–1984 were then available, as well as other data collected during the previous crisis of 1970; a comprehensive picture of the variations observed before, during and after the acceleration of vertical movement has been drawn.According to the results obtained, the intrusion of a magmatic body as the trigger of the observed ground deformation is considered unrealistic. The whole area appears now in a quiet stage, and no further perturbation is expected without previous significant tectonic activity; chemical precursors appear suitable for an early detection of changes occurring at depth, to forecast possible consequences to be expected in the surface environment.     

1997年广东台山小震群特征

分析了１９９７年１１￣１２月在广东台山市三合镇附近发生的最大震级为４．１级小震群的活动特征、地质构造背景和震源机制解,并将其与１９７０年７￣１２月发生的最大震级为４．０级的台山震群进行了对比,计算了两次小震群的序列特征参数,结果表明,１９９７年震群具有前兆震群的某些特征。     

The design of visco‐acoustic weighted L1‐error frequency–space wavefield extrapolators

Seismic imaging is an important step for imaging the subsurface structures of the Earth. One of the attractive domains for seismic imaging is explicit frequency–space (f – x) prestack depth migration. So far, this domain focused on migrating seismic data in acoustic media, but very little work assumed visco‐acoustic media. In reality, seismic exploration data amplitudes suffer from attenuation. To tackle the problem of attenuation, new operators are required, which compensates for it. We propose the weighted L ₁ ‐error minimisation technique to design visco‐acoustic f – x wavefield extrapolators. The L ₁ ‐error wavenumber responses provide superior extrapolator designs as compared with the previously designed equiripple L ₄ ‐norm and L_∞‐norm extrapolation wavenumber responses. To verify the new compensating designs, prestack depth migration is performed on the challenging Marmousi model dataset. A reference migrated section is obtained using non‐compensating f – x extrapolators on an acoustic dataset. Then, both compensating and non‐compensating extrapolators are applied to a visco‐acoustic dataset, and both migrated sections are then compared. The final images show that the proposed weighted L ₁ ‐error method enhances the resolution and results in practically stable images.     

Evaluation of site effects in some localities of ‘Alta Val Tiberina Umbra’ (Italy) by numerical analysis

In the paper the application of a methodology for the evaluation of site effects in an area of Umbria Region (Italy) is shown. In the project 20 localities were analyzed. In this paper the results of some representative localities are presented. The objective of the project was to develop a methodology that may be easily repeated, in order to take into account site effects in urban planning. Therefore a series of geologic, geomorphologic (1:5.000 scale) and geotechnical analyses have been carried out, to identify the areas affected by site effects and to characterize the lithotechnical units. The expected seismic inputs have been calculated and the numerical analyses 1D and 2D have been done. The results, in terms of elastic pseudo-acceleration spectra and amplification coefficients, as a ratio between spectral intensity of output and input, give elements for urban planning, both for urban general choice and for buildings design.