Journal of Seismology and Earthquake Engineering
Volume:19 Issue: 3, Autumn 2017

Ongoing research in the development of design philosophies for earthquake resistant structures over the past few decades was initially based on the strength and elastic analysis. Later, design philosophies recognized the deformation to be an important parameter to be considered in design following nonlinear analysis. The maximum design lateral force, for a particular earthquake, acting on structures having multiple natural time periods can be obtained from inelastic response spectrum. Scenario earthquakes characterize the spatio-temporal evolution of fault rupture, which when solved together with the elastodynamic equations can give the acceleration time-history at any point on the surface. For any tectonic regime, based on the past seismicity, a seismogenic depth could be defined based on the depth below which no occurrence of earthquakes was observed in the past. Fixing a certain magnitude, we prescribe the slip on a vertical fault based on statistical relations that exist in literature, and simulate ground motion. The ruptured region is varied, is initially assumed to be closer to the free surface, and is later lowered deeper in intervals of 10 km to emulate larger seismogenic depths. Using the simulated ground motion, we compute the fundamental entity of earthquake engineering: the response spectrum for five depths of hypocenter. Earthquake resistant design of structures is mostly done to allow for large inelastic deformations, giving ductile detailing. Choosing ductility ratios of 2, 4, 6 and 8, this paper describes dependency of elastic and inelastic horizontal spectral acceleration on seismogenic depth, by considering kinematic rupture description of a Mw 6.5 earthquake on a vertical strike slip fault.

In the specific barrier model (SBM) as an earthquake source model, fault is assumed as a rectangle whose surface is covered by an aggregate of circular cracks of equal diameter (primary version) on which a local stress drop takes place to simulate high-frequency movements. Seismic moment in the SBM is computed in a deterministic manner on the fault plane, on the basis of moment and area constraints. In the SBM, rupture on cracks causes a stress drop that moves within circular cracks, and rupture tip sweeps the fault plane. In this paper, new time functions for inclined faults have been developed. The mentioned time functions have been obtained by using probability density functions (PDFs) of arrival time based on site positions, fault geometry and fault rotation angle. Finally, to calculate source spectra, PDFs of sub-events' size are assumed to be fractal. Various parameter studies are then conducted to show different features of the proposed PDFs on the results of the SBM.

The main goal of an Earthquake Early Warning (EEW) system is to reduce the damaging effects of the hazardous earthquakes. The characterization of an earthquake for EEW includes most importantly, the estimates of its size (magnitude) and location. In this study, the distance and magnitude of the selected earthquakes were estimated using the envelope of the initial part of the P-waveforms deploying a single seismic record. The method so called "B-delta" [1] is used to find the EEW parameters. In total, 1210 records (vertical component) with 4.0 £M 7.7 and epicentral distance up to 300 km is used. The root mean square error (RMSE) of epicentral distance estimations using 2 and 3 sec P-wave time windows are 0.260 and 0.261 on a logarithmic scale respectively. Additionally, the C-D method [2] was performed to check if this method provides more accurate estimates. Results show no significant differences between the final estimates of the two methods. Furthermore, using the obtained epicentral distance, the magnitude was estimated by employing empirical magnitude-amplitude relationships. The magnitude RMSE of both methods is in range of 0.6-0.7. Results suggest that the final magnitude of the large events would be underestimated using just few seconds of P-wave; however, the magnitude estimates can be used as the minimum threshold for the final size of the ongoing event. Moreover, short term average/long term average method was used for automatic P-wave arrival detection. The result shows 76% success in P-wave arrival detection. This method can be utilized in real time EEW practices.

In this paper, permanent displacement of anchor-reinforced slopes was studied numerically to investigate the effect of weak layer on the seismic stability. A variety of slopes with different height and reinforcing anchors were surveyed by employing three different (1) dynamic finite element, (2) Newmark's sliding block and (3) simplified analytical formula. The position and properties of the weak layer was determined by "Phi-C-Reduction" method. Several time-history analyses were performed for the selected slopes subjected to two devastating earthquakes (Tabas and Kocaeli) at different intensities. It was shown that when there is a weak layer in anchor-reinforced slopes, which are statically stable with reasonable safety factor, the anchors could not necessarily provide seismic stability for slopes in some intensity levels. Furthermore, considering average acceleration that may be amplified throughout the slope, the resonance phenomenon was investigated.

Two destructive earthquakes occurred on the 11th of August 2012 in the regions of Ahar and Varzaghan, NW Iran. High-frequency strong-motion data of these earthquakes have been analyzed to determine the Qβ (f) and source parameters by inversion of the recorded data. The data from a local network of 21 acceleration records, for the first main shock and 19 records for the second main shock was used to estimate Q-relationship in 30 stations. The seismic hazard map for this region illustrates that most of the area in this province is located within high relative risk and characterized by a large number of heterogeneities. For frequency band of 1 to 20 HZ, the frequency-dependent attenuation for this region found to be Qβ = (94±29) f (0.82±0.05). The authenticity of achieved Qβ (f) relation is checked by comparing the source spectra in various stations with the theoretical spectra. Low values of the coefficient (Q < 200) in the Qβ (f) relation suggest that the region is seismically and tectonically active. The present inversion of strong-motion data gives the source parameters. The corner frequencies and stress drops are calculated as fc1= 0.08[HZ],fc2= 0.11[HZ], Δσ1=77.14[bar] and Δσ2=33.06[bar], respectively.

In this research, the performance abilities associated with tube type lateral load resistant framed systems are studied in order to assess the seismic response parameters of steel tall buildings under both far and near-field records. For this purpose, four 30 story structural models with separated framed tube-based skeletons were selected and designed. The structural models have been designed according to the Iranian seismic code 2800 (4th edition). The structural response parameters have been computed and obtained by conducting a number of non-linear dynamic time history analyses. Based on the analytical results obtained from nonlinear analyses, the values of maximum inter-story drift, story acceleration and velocity, dynamic base shear, configuration of plastic hinges mechanism, shear lag phenomena and residual drift were assessed and investigated. Yet, the results have been discussed and compared with the “life safety” and “collapse prevention” performance limits, as recommended by Fema 356. Findings from this study reveal that mean maximum demands and the dispersion in the peak values were considerably higher for near-fault records than far-fault motions. The obtained results indicate the fact that an appropriate arrangement and bundled configuration of interior rigid frames could remarkably reduce the appearance of shear lag phenomenon almost up to 70% as compared to the corresponding results with basic framed tube.