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1.
Ground motion intensity measures such as the peak ground acceleration (PGA) and the pseudo-spectral acceleration (PSA) at two sites due to the same seismic event are correlated. The spatial correlation needs to be considered when modeling ground-motion fields for seismic loss assessments, since it can have a significant influence on the statistical moments and probability distribution of aggregated seismic loss of a building portfolio.Empirical models of spatial correlation of ground motion intensity measures exist only for a few seismic regions in the world such as Japan, Taiwan and California, since for this purpose a dense observation network of earthquake ground motion is required. The Istanbul Earthquake Rapid Response and Early Warning System (IERREWS) provides one such dense array with station spacing of typically 2 km in the urban area of Istanbul. Based on the records of eight small to moderate (Mw3.5–Mw5.1) events, which occurred since 2003 in the Marmara region, we establish a model of intra-event spatial correlation for PGA and PSA up to the natural period of 1.0 s.The results indicate that the correlation coefficients of PGA and short-period PSA decay rapidly with increasing interstation distance, resulting in correlation lengths of approximately 3–4 km, while correlation lengths at longer natural periods (above 0.5 s) exceed 6 km. Finally, we implement the correlation model in a Monte Carlo simulation to evaluate economic loss in Istanbul's district Zeytinburnu due to a Mw7.2 scenario earthquake.  相似文献   

2.
The seismic history of the city of Ragusa (Italy), the geotechnical characterisation of the subsoil and the site response analysis should be correctly evaluated for the definition of the Seismic Geotechnical Hazard of the city of Ragusa, through geo-settled seismic microzoning maps. Basing on the seismic history of the city of Ragusa, the following earthquake scenarios have been considered: the “Val di Noto” earthquake of January 11, 1693 (with intensity X–XI on MCS scale, magnitude MW=7.41 and epicentral distance of about 53 km); the “Etna” earthquake of February 20, 1818 (with intensity IX on MCS scale, magnitude MW=6.23 and epicentral distance of about 64 km); the Vizzini earthquake of April 13, 1895 (with intensity I=VII–VIII on MCS scale, magnitude MW=5.86 and epicentral distance of about 26 km); the “Modica” earthquake of January 23, 1980 (with intensity I=V–VI on MCS scale, magnitude MW=4.58 and epicentral distance of about 10 km); the “Sicilian” earthquake of December 13, 1990 (with intensity I=VII on MCS scale, magnitude MW=5.64 and epicentral distance of about 50 km). Geotechnical characterisation has been performed by in situ and laboratory tests, with the definition of shear wave velocity profiles in the upper 30 m of soil. Soil response analyses have been evaluated for about 120 borings location by some non-linear 1-D models. Finally the seismic microzonation of the city of Ragusa has been obtained in terms of maps with different peak ground acceleration at the surface; shaking maps for the central area of the city of Ragusa were generated via GIS for the earthquake scenarios.  相似文献   

3.
Serpentinization of the mantle wedge is an important process that influences the seismic and mechanical properties in subduction zones. Seismic detection of serpentines relies on the knowledge of elastic properties of serpentinites, which thus far has not been possible in the absence of single-crystal elastic properties of antigorite. The elastic constants of antigorite, the dominant serpentine at high-pressure in subduction zones, were measured using Brillouin spectroscopy under ambient conditions. In addition, antigorite lattice preferred orientations (LPO) were determined using an electron back-scattering diffraction (EBSD) technique. Isotropic aggregate velocities are significantly lower than those of peridotites to allow seismic detection of serpentinites from tomography. The isotropic VP/VS ratio is 1.76 in the Voigt–Reuss–Hill average, not very different from that of 1.73 in peridotite, but may vary between 1.70 and 1.86 between the Voigt and Reuss bonds. Antigorite and deformed serpentinites have a very high seismic anisotropy and remarkably low velocities along particular directions. VP varies between 8.9 km s? 1 and 5.6 km s? 1 (46% anisotropy), and 8.3 km s? 1 and 5.8 km s? 1 (37%), and VS between 5.1 km s? 1 and 2.5 km s? 1 (66%), and 4.7 km s? 1 and 2.9 km s? 1 (50%) for the single-crystal and aggregate, respectively. The VP/VS ratio and shear wave splitting also vary with orientation between 1.2 and 3.4, and 1.3 and 2.8 for the single-crystal and aggregate, respectively. Thus deformed serpentinites can present seismic velocities similar to peridotites for wave propagation parallel to the foliation or lower than crustal rocks for wave propagation perpendicular to the foliation. These properties can be used to detect serpentinite, quantify the amount of serpentinization, and to discuss relationships between seismic anisotropy and deformation in the mantle wedge. Regions of high VP/VS ratios and extremely low velocities in the mantle wedge of subduction zones (down to about 6 and 3 km.s?1 for VP and VS, respectively) are difficult to explain without strong preferred orientation of serpentine. Local variations of anisotropy may result from kilometer-scale folding of serpentinites. Shear wave splittings up to 1–1.5 s can be explained with moderately thick (10–20 km) serpentinite bodies.  相似文献   

4.
Many authors have proposed that the study of seismicity rates is an appropriate technique for evaluating how close a seismic gap may be to rupture. We designed an algorithm for identification of patterns of significant seismic quiescence by using the definition of seismic quiescence proposed by Schreider (1990). This algorithm shows the area of quiescence where an earthquake of great magnitude may probably occur. We have applied our algorithm to the earthquake catalog on the Mexican Pacific coast located between 14 and 21 degrees of North latitude and 94 and 106 degrees West longitude; with depths less than or equal to 60 km and magnitude greater than or equal to 4.3, which occurred from January, 1965 until December, 2014. We have found significant patterns of seismic quietude before the earthquakes of Oaxaca (November 1978, Mw = 7.8), Petatlán (March 1979, Mw = 7.6), Michoacán (September 1985, Mw = 8.0, and Mw = 7.6) and Colima (October 1995, Mw = 8.0). Fortunately, in this century earthquakes of great magnitude have not occurred in Mexico. However, we have identified well-defined seismic quiescences in the Guerrero seismic-gap, which are apparently correlated with the occurrence of silent earthquakes in 2002, 2006 and 2010 recently discovered by GPS technology.  相似文献   

5.
The late Triassic to early Tertiary Coast Mountains Batholith (CMB) of British Columbia provides an ideal locale to study the processes whereby accreted terranes and subduction-related melts interact to form stable continental crust of intermediate to felsic composition and complementary ultramafic residuals. Seismic measurements, combined with calculated elastic properties of various CMB rock compositions, provide a window into the deep-crustal lithologies that are key to understanding the processes of continental growth and evolution. We use a combination of seismic observations and petrologic modeling to construct hypothetical crustal sections at representative locations across the CMB, then test the viability of these sections via forward modeling with synthetic seismic data. The compositions that make up our petrologic forward models are based on calculations using the free energy minimization program Perple_X to predict mineral assemblages at depth for the bulk compositions of exposed plutonic rocks collected in the study area. Seismic data were collected along two transects in west-central British Columbia: a southern line that crossed the CMB near the town of Bella Coola (near 52° N), and a northern line centered on the towns of Terrace and Kitimat (near 54° N). Along both transects, seismic receiver functions reveal high Vp/Vs ratios near the Insular/Intermontane terrane boundary and crustal thickness increasing from 26 ± 3 km to 34 ± 3 km (at the 1 sigma certainty level) from west to east across the Coast Shear Zone (CSZ). On the southern line, we observe an anomalous region of complex receiver functions and diminished Moho signals beneath the central portion of the CMB. Our petrologic and seismic profiles show that observed seismic data from much of the CMB can be well-matched in terms of crustal thickness and structure, average Vp/Vs, and amplitude of the Moho converted phase, without including ultramafic residual material in the lower crust.  相似文献   

6.
The city of Catania (Italy) in the South-Eastern Sicily has been affected in past times by several destroying earthquakes with high values of estimated magnitude. The seismogenic area to the south of Volcano Etna, known as Iblean Area, is placed between the African and the Euro-Asiatic plates on the west of the Ibleo-Maltese escarpment, to the south of the Graben of the Sicilian channel and on the east of the overlapping front of Gela. Basing on the seismic history of Catania, the following earthquake scenarios have been considered: the “Val di Noto” earthquake of January 11, 1693 (with intensity X-XI on MCS scale, magnitude MW=7.41 and epicentral distance of about 13 km); the “Etna” earthquake of February 20, 1818 (with intensity IX on MCS scale, magnitude MW=6.23 and epicentral distance of about 10 km). The soil response analysis at the surface, in terms of time history and response spectra, has been obtained by 1-D equivalent linear models for about 1200 borings location available in the data-bank of the central area of Catania of about 50 km2, using deterministic design scenario earthquakes as input at the conventional bedrock.Seismic microzoning maps of the city of Catania have been obtained in terms of different peak ground acceleration at the surface and in terms of amplification ratios for given values of frequency.  相似文献   

7.
Inversion of local earthquake travel times and joint inversion of receiver functions and Rayleigh wave group velocity measurements were used to derive a simple model for the velocity crustal structure beneath the southern edge of the Central Alborz (Iran), including the seismically active area around the megacity of Tehran. The P and S travel times from 115 well-located earthquakes recorded by a dense local seismic network, operated from June to November 2006, were inverted to determine a 1D velocity model of the upper crust. The limited range of earthquake depths (between 2 km and 26 km) prevents us determining any velocity interfaces deeper than 25 km. The velocity of the lower crust and the depth of the Moho were found by joint inversion of receiver functions and Rayleigh wave group velocity data. The resulting P-wave velocity model comprises an upper crust with 3 km and 4 km thick sedimentary layers with P wave velocities (Vp) of ～5.4 and ～5.8 km s?1, respectively, above 9 km and 8 km thick layers of upper crystalline crust (Vp ～6.1 and ～6.25 km s?1 respectively). The lower crystalline crust is ～34 km thick (Vp ～ 6.40 km s?1). The total crustal thickness beneath this part of the Central Alborz is 58 ± 2 km.  相似文献   

8.
On February 27, 2010 an earthquake of magnitude Mw=8.8, with epicenter in Cobquecura, Maule region, hit the central part of Chile. After the earthquake, a tsunami occurred that caused heavy casualties and damage to buildings and infrastructure. In particular, 4.5% of the overpasses located in the affected region suffered some type of damage and 25 bridges and several pedestrian bridges collapsed. At that time, there were about a dozen bridges with seismic isolation bearings in Chile, two of which were instrumented with accelerometer networks: the Marga Marga Bridge, located in Viña del Mar, and an elevated section of the Metro Line 5 in Santiago, at approximately 300 km and 400 km from the epicenter, respectively. This paper analyzes the acceleration records obtained at these instrumented structures and studies the effect of the seismic isolation on their dynamic response. The beneficial effect of the isolation system, especially in the longitudinal direction, is apparent. In addition, some flaws in the collapsed bridges are described.  相似文献   

9.
R/S analysis is used in this work to investigate the fractal correlations in terms of the Hurst exponent for the 1998–2011 seismicity data in Southern Mexico. This region is the most seismically active area in Mexico, where epicenters for severe earthquakes (e.g., September 19, 1985, Mw = 8.1) causing extensive damage in highly populated areas have been located. By only considering the seismic events that meet the Gutenberg–Ritcher law completeness requirement (b = 0.97, MGR = 3.6), we found time clustering for scales of about 100 and 135 events. In both cases, a cyclic behavior with dominant spectral components at about one cycle per year is revealed. It is argued that such a one-year cycle could be related to tidal effects in the Pacific coast. Interestingly, it is also found that high-magnitude events (Mw ≥ 6.0) are more likely to occur under increased interevent correlations with Hurst exponent values H > 0.65. This suggests that major earthquakes can occur when the tectonic stress accumulates in preferential directions. In contrast, the high-magnitude seismic risk is reduced when stresses are uniformly distributed in the tectonic shell. Such cointegration between correlations (i.e., Hurst exponent) and macroseismicity is confirmed for spatial variations of the Hurst exponent. In this way, we found that, using the Hurst exponent standpoint, the former presumed Michoacan and the Guerrero seismic gaps are the riskiest seismic zones. To test this empirical finding, two Southern Mexico local regions with large earthquakes were considered. These are the Atoyac de Alvarez, Guerrero (Mw = 6.3), and Union Hidalgo, Oaxaca (Mw = 6.6), events. In addition, we used the Loma Prieta, California, earthquake (October 17, 1989, Mw = 6.9) to show that the high-magnitude earthquakes in the San Andreas Fault region can also be linked to the increments of determinism (quantified in terms of the Hurst exponent) displayed by the stochastic dynamics of the interevent period time series. The results revealed that the analysis of seismic activity by means of R/S analysis could provide further insights in the advent of major earthquakes.  相似文献   

10.
We used data of local earthquakes collected during two recent passive seismic experiments carried out in southern Italy in order to study the seismotectonic setting of the Lucanian Apennine and the surrounding areas. Based on continuous recordings of the temporary stations we extracted over 15,600 waveforms, which were hand-picked along with those recorded by the permanent stations of the Italian national seismic network obtaining a dense, high-quality dataset of P- and S-arrival times. We examined the seismicity occurring in the period 2001–2008 by relocating 566 out of 1047 recorded events with magnitudes ML ≥ 1.5 and computing 162 fault-plane solutions. Earthquakes were relocated using a minimum one-dimensional velocity model previously obtained for the region and a Vp/Vs ratio of 1.83. Background seismicity is concentrated within the upper crust (between 5 and 20 km of depth) and it is mostly clustered along the Lucanian Apennine chain axis. A significant feature extracted from this study relates to the two E–W trending clusters located in the Potentino and in the Abriola–Pietrapertosa sector (central Lucania region). Hypocentral depths in both clusters are slightly deeper than those observed beneath the Lucanian Apennine. We suggest that these two seismic features are representative of the transition from the inner portion of the chain to the external margin characterized by dextral strike-slip kinematics. In the easternmost part of the study area, below the Bradano foredeep and the Apulia foreland, seismicity is generally deeper and more scattered. The sparse seismicity localized in the Sibari Plain, in the offshore area along the northeastern Calabrian coast and in the Taranto Gulf is also investigated thanks to the new recordings. This seismicity shows hypocenters between 12 and 20 km of depth below the Sibari Plain and is deeper (foci between 10 and 35 km of depth) in the offshore area of the Taranto Gulf. 102 well-constrained fault-plane solutions, showing predominantly normal and strike-slip character with tensional axes (T-axes) generally NE oriented, were selected for the stress tensor analysis. We investigated stress field orientation inverting focal mechanism belonging to the Lucanian Apennine and the Pollino Range, both areas characterized by a more concentrated background seismicity.  相似文献   

11.
Modeling of multimode surface wave group velocity dispersion data sampling the eastern and the western Ganga basins, reveals a three layer crust with an average Vs of 3.7 km s?1, draped by ～2.5 km foreland sediments. The Moho is at a depth of 43 ± 2 km and 41 ± 2 km beneath the eastern and the western Ganga basins respectively. Crustal Vp/Vs shows a felsic upper and middle crust beneath the eastern Ganga basin (1.70) compared to a more mafic western Ganga basin crust (1.77). Due to higher radiogenic heat production in felsic than mafic rocks, a lateral thermal heterogeneity will be present in the foreland basin crust. This heterogeneity had been previously observed in the north Indian Shield immediately south of the foreland basin and must also continue northward below the Himalaya. The high heat producing felsic crust, underthrust below the Himalayas could be an important cause for melting of midcrustal rocks and emplacement of leucogranites. This is a plausible explanation for abundance of leucogranites in the east-central Himalaya compared to the west. The uppermost mantle Vs is also significantly lower beneath the eastern Ganga basin (4.30 km s?1) compared to the west (4.44 km s?1).  相似文献   

12.
Two-dimensional crustal velocity models are derived from passive seismic observations for the Archean Karelian bedrock of north-eastern Finland. In addition, an updated Moho depth map is constructed by integrating the results of this study with previous data sets. The structural models image a typical three-layer Archean crust, with thickness varying between 40 and 52 km. P wave velocities within the 12–20 km thick upper crust range from 6.1 to 6.4 km/s. The relatively high velocities are related to layered mafic intrusive and volcanic rocks. The middle crust is a fairly homogeneous layer associated with velocities of 6.5–6.8 km/s. The boundary between middle and lower crust is located at depths between 28 and 38 km. The thickness of the lower crust increases from 5–15 km in the Archean part to 15–22 km in the Archean–Proterozoic transition zone. In the lower crust and uppermost mantle, P wave velocities vary between 6.9–7.3 km/s and 7.9–8.2 km/s. The average Vp/Vs ratio increases from 1.71 in the upper crust to 1.76 in the lower crust.The crust attains its maximum thickness in the south-east, where the Archean crust is both over- and underthrust by the Proterozoic crust. A crustal depression bulging out from that zone to the N–NE towards Kuusamo is linked to a collision between major Archean blocks. Further north, crustal thickening under the Salla and Kittilä greenstone belts is tentatively associated with a NW–SE-oriented collision zone or major shear zone. Elevated Moho beneath the Pudasjärvi block is primarily explained with rift-related extension and crustal thinning at ∼2.4–2.1 Ga.The new crustal velocity models and synthetic waveform modelling are used to outline the thickness of the seismogenic layer beneath the temporary Kuusamo seismic network. Lack of seismic activity within the mafic high-velocity body in the uppermost 8 km of crust and relative abundance of mid-crustal, i.e., 14–30 km deep earthquakes are characteristic features of the Kuusamo seismicity. The upper limit of seismicity is attributed to the excess of strong mafic material in the uppermost crust. Comparison with the rheological profiles of the lithosphere, calculated at nearby locations, indicates that the base of the seismogenic layer correlates best with the onset of brittle to ductile transition at about 30 km depth.We found no evidence on microearthquake activity in the lower crust beneath the Archean Karelian craton. However, a data set of relatively well-constrained events extracted from the regional earthquake catalogue implies a deeper cut-off depth for earthquakes in the Norrbotten tectonic province of northern Sweden.  相似文献   

13.
On 6 April 2009 a Mw=6.1 earthquake produced severe destruction and damage over the historic center of L’Aquila City (central Italy), in which the accelerometer stations AQK and AQU recorded a large amount of near-fault ground motion data. This paper analyzes the recorded ground motions and compares the observed peak accelerations and the horizontal to vertical response spectral ratios with those revealed from numerical simulations. The finite element method is considered herein to perform dynamic modeling on the soil profile underlying the seismic station AQU. The subsurface model, which is based on the reviewed surveys that were carried out in previous studies, consists of 200–400 m of Quaternary sediments overlying a Meso-Cenozoic carbonate bedrock. The Martin-Finn-Seed's pore-water pressure model is used in the simulations. The horizontal to vertical response spectral ratio that is observed during the weak seismic events shows three predominant frequencies at about 14 Hz, 3 Hz and 0.6 Hz, which may be related to the computed seismic motion amplification occurring at the shallow colluvium, at the top and base of the fluvial-lacustrine sequence, respectively. During the 2009 L’Aquila main shock the predominant frequency of 14 Hz shifts to lower values probably due to a peculiar wave-field incidence angle. The predominant frequency of 3 Hz shifts to lower values when the earthquake magnitude increases, which may be associated to the progressive softening of soil due to the excess pore-water pressure generation that reaches a maximum value of about 350 kPa in the top of fluvial-lacustrine sequence. The computed vertical peak acceleration underestimates the experimental value and the horizontal to vertical peak acceleration ratio that is observed at station AQU decreases when the earthquake magnitude increases, which reveals amplification of the vertical component of ground motion probably due to near-source effects.  相似文献   

14.
It is understood that sample size could be an issue in earthquake statistical studies, causing the best estimate being too deterministic or less representative derived from limited statistics from observation. Like many Bayesian analyses and estimates, this study shows another novel application of the Bayesian approach to earthquake engineering, using prior data to help compensate the limited observation for the target problem to estimate the magnitude of the recurring Meishan earthquake in central Taiwan. With the Bayesian algorithms developed, the Bayesian analysis suggests that the next major event induced by the Meishan fault in central Taiwan should be in Mw 6.44±0.33, based on one magnitude observation of Mw 6.4 from the last event, along with the prior data including fault length of 14 km, rupture width of 15 km, rupture area of 216 km2, average displacement of 0.7 m, slip rate of 6 mm/yr, and five earthquake empirical models.  相似文献   

15.
The elastic moduli of polycrystalline ringwoodite, (Mg0.91Fe0.09)2SiO4, were measured up to 470 K by means of the resonant sphere technique. The adiabatic bulk (KS) and shear (μ) moduli were found to be 185.1(2) and 118.22(6) GPa at room temperature, and the average slopes of dKS/dT and dμ/dT in the temperature range of the study were determined to be −0.0193(9) and −0.0148(3) GPa/K, respectively. Using these results, we estimate seismic wave velocity jumps for a pure olivine mantle model at 520 km depth. We find that the jump for the S-wave velocity is about 1.5 times larger than that for the P-wave velocity at this depth. This suggests that velocity jumps at the 520 km discontinuity are easier to detect using S-waves than P-waves.  相似文献   

16.
The source parameters of the major events of a swarm and of two seismic sequences, occurred in the Friuli area (Northeastern Italy) and in Western Slovenia, were estimated. The Claut swarm (C96) occurred since the end of January to June 1996, with a MD 4.3 major shock and it appears composed of three sub-sequences. The two sequences are the Kobarid sequence (K98) started on April 12, 1998 with a MD 5.6 mainshock and the M.te Sernio (S02) sequence caused by the February 14, 2002 earthquake (MD = 4.9). Acceleration and velocity data recorded by the local seismic network of the Istituto Nazionale di Oceanografia e di Geofisica Sperimenale (OGS) and corrected for attenuation, were employed to estimate seismic moments and radiated energies. Source dimensions were inferred from the computed corner frequencies and the stress release was estimated from the Brune stress drop, the apparent stress and the RMS stress drop. On the whole, seismic moments range from 1.7 × 1012 to 1.1 × 1017 N m, and radiated energies are in the range 106–1013 J. Brune stress drops are scattered and do not show any evidence of a self-similarity breakdown for sources down to 130 m radius. The radiated seismic energy scales as a function of seismic moment, with a slope of the scaling relation that decreases for increasing seismic moments.The mechanism of stress release was analyzed by computing the ɛ parameter of Zuniga [Zuniga, R., 1993. Frictional overshoot and partial stress drop. Which one? Bull. Seismol. Soc. Am. 83, 939–944]. The K98 and S02 sequences are characterized by a wide range of the ɛ parameter with stress drop mechanism varying from partial locking to overshoot cases. The ɛ values of the C96 swarm are more homogeneous and close to the Orowan's condition. The radiated seismic energy and the ratio of stress drop between mainshock and aftershocks appear different among the analyzed cases. We therefore investigated the relationship between the stress parameters of the main shock and the energy radiated by the aftershock sequences. For this purpose, we also estimated the source parameters of two other sequences occurred in the area, with mainshocks of MD 4.1 and 5.1, respectively. We found a positive correlation between the Brune stress drop of the mainshock and the ratio between the radiated energy of the mainshock and the summation of the energies radiated by the aftershocks.  相似文献   

17.
This is an attempt to analyze the current lithospheric stress pattern in the Baikal rift in terms of nonlinear dynamics as an open self-organizing system in order to gain more insights into the general laws of regional seismicity. According to the suggested approach, the stress pattern inferred from seismic moments of 70,000 MLH ≥ 2.0 events that occurred in the region between 1968 and 1994 is presented as a phase portrait in the phase spaces of the seismic moments. The obtained phase portrait of the system evolution fits well a scenario with triple equilibrium bifurcation where stress bifurcations account for the frequency of M > 5.5 earthquakes. Extrapolation of the results into the nearest future indicates probability of such a bifurcation (a catastrophe of stress), i.e., there is growing risk that M ≈ 7 events may happen in the region within a few years.  相似文献   

18.
Regional site conditions relevant for seismic hazard studies can be derived from various geologic, seismologic, and geotechnical sources. In this study, site conditions are derived for the Ankara Basin in Turkey by merging in-situ seismic measurements of dynamic properties, geologic information, and some geotechnical boring information. Field seismic refraction surveys were performed at 259 sites in the project area to classify and characterize Plio–Pleistocene fluvial deposits and Quaternary alluvial and terrace deposits. The shear-wave velocity profiles of the near-surface geologic units are used to characterize site classes according to the International Building Code [International Code Council, ICC. International Building Code. Structural and fire- and life-safety provisions (seismic, wind, accessibility, egress, occupancy and roof codes), 2006. Whittier, CA.] and the Turkish Seismic Code [Ministry of Public Works and Settlement, 1998. Turkish Seismic Code, Specification for Structures to be Built in Disaster Areas, Ankara, Turkey], and to develop a regional model for the average shear-wave velocity in the top 30 m. The resulting maps of site class indicate that the classification system for the Turkish Seismic Code results in a significant portion of the Ankara Basin being classified as Z4, the softest site class. The International Building Code site classification system results in most of the Ankara Basin being classified as D, stiff soil. These differences are caused by the Turkish Seismic Code incorporating information from only the surface layer, while the International Building Code incorporates information from the top 30 m.  相似文献   

19.
Strong ground motion variability due to rapid changes in subsoil conditions may lead to different site responses, which in turn yields to beneficial or detrimental soil–foundation–structure interaction. This technical note presents the results of a seismic soil–structure interaction analysis conducted using a 2D finite difference model, developed with the program FLAC, of a critical section of a 60 km long strategic urban overpass, which is under construction in Mexico City, for a Mw 8.7 earthquake. Initially, the response of the free field was calibrated comparing the values obtained with FLAC, with those gathered using the computer code QUAD4M. Good agreement was observed between the results generated with these programs. Accelerations and displacements were determined at the upper deck and foundation of the urban overpass. Important seismic soil–structure interaction was observed along the overpass at the supports analyzed. This numerical study helps to gain insight regarding the site response ground motion incoherence effects that influence the dynamic behavior of this kind of structures during extreme events.  相似文献   

20.
This paper focuses on using high-frequency GAP-SENSORs (GSs), accelerometers, and load cells in a laminar shear box (LSB) filled with loose Toyoura sand to understand the effects of impact loads and cyclic shaking at 1-G on soil properties. The shear wave velocity at small strain (Vs) was calculated directly from first arrival reference using displacement time-history of two GSs under impact loading. Moreover, from first peak using the reduced deformation amplitude technique, damping ratio was calculated. In addition, shaking table tests were performed under harmonic loading with amplitude of acceleration inside the model ground varying from 0.02 g to 1 g. The frequencies of excitation varied from 1 Hz to 10 Hz. GSs and inside accelerometers were used to directly measure the outside lateral deformation and shear stress at different elevations of LSB, respectively. Results show that the shear modulus (G) and the damping ratio (D) behavior of model sand are generally consistent with the behavior presented by similar tests using only accelerometers. In addition, damping ratio increases as frequency loading increases. Characteristic changes in two shear stress components in shaking loading conditions were also investigated using high precision inside load cells.  相似文献   

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