Seismic site effect estimation in the city of Rabat (Morocco

Journal of Earthquake Engineering, 2008

Measurements of background noise at Al Hoceima city and its extension zones allowed us to elaborate a seismic microzonation map. The analysis of this map shows existing relationships between the observed dominant periods and the local geological conditions. In particular, a strong correlation between the dominant periods and the topography is apparent; indeed, we find larger dominant periods in areas with higher topography such as in the Ras El Abed sector to the north of the city and in the area of Cala Bonita, south of the city. Furthermore, the field work conducted in the region revealed that the karstic phenomenon is well developed in the Ras El Abed sector, and affects the dominant periods and a hence the site response.

Site characteristics, site-specific analyses and Seismic microzonation were conducted in Boshehr, the south cities of Iran, which are the main steps towards a seismic risk analysis and mitigation strategy. It is essential to obtain a proper understanding of the local subsurface conditions. In situ test included boreholes at 15 stations, seismic refraction surveys at 13 stations, geo-electrical profiling at 13 stations, deep seismic down-hole surveys at 2 stations and microtremor measurements at 11 stations. Through linking of the ground model with a seismic response modeling program such as SHAKE, it is possible to obtain a delineation of the spatial variation in seismic responses. This can be used as a basis for seismic micro-zonation mapping. As result, Distribution maps of site periods and peak ground acceleration throughout the area were developed, providing a useful basis for land-use planning in this area.

Annals of Geophysics, 2011

Mashhad city has a substantial risk of earthquakes due to the potential of the underlying soft soils to amplify ground motions. It is therefore imperative to conduct detailed seismic hazard assessment of the area (seismic microzonation). Seismic microzonation of big cities, like Mashhad, provides a basis for site-specific hazard analysis. In the present study, microtremor observations were carried out at 90 sites in the east part of Mashhad city. The predominant frequency and spectral ratio amplitude of the ground were determined by the Nakamura technique, and a microzonation map was developed for Mashhad on the basis of the variations of the predominant frequency and spectral ratio amplitude of the ground. Soil texture and N-value standard-penetration-test (N-SPT) maps and sections were prepared for different depths below the city, by analysis and interpolation of data collected in the study area from 169 boreholes. Then the predominant frequency variations were compared with soil texture and N-SPT variations for four sections in different directions in the study area. This comparison shows that with decreasing soil softening and N-SPT values, the soil predominant frequency also decreases.

Egypt has suffered great damage due to earthquakes from near and distant sources, both in historical and recent times. Seismic microzonation one of the vital engineering studies because it has a great effect on structure bases. In this study, Hurghada was chosen as a city and its famous ground motion (Shedwan earthquake (31/03/1969)). The objectives of this study are: Draw the microzoning map to Hurghada city by using computer finite element program, estimation of the dynamic properties of the soil layer, evaluation of the foundation material characteristics and defining both the fundamental resonance frequency and the amplification characteristics of ground vibration at Hurghada city to protect the structures from damages related to earthquakes.

Open Journal of Geology, 2012

As an important step in effectively reducing seismic risk and the vulnerability of the city of Mobarakeh to earthquakes, a site effect microzonation Study was conducted. Seismic hazard analysis for a return period of 475 years was carried out. Data from 10 borings was collected and analyzed, geophysical surveys were conducted and seismology and geoelectric measurements taken in more than 17 stations through out the city. The study area was divided into a grid of 500 × 500 m 2 elements and the sub-surface ground conditions were classified into 5 representative geotechnical profiles. Electric resistivity was measured in close to 17 geotechnical boreholes and surface and sub-surface sediments were collected and analyzed. Site response analyses were carried out on each representative profile using 30 different base rock input motions. Distribution maps of site periods and peak ground acceleration and old and new texture buildings through out the city were developed, providing a useful basis for land-use planning in the city.

Journal of Engineering Sciences, Assiut University, Faculty of Engineering, Vol. 42, No. 1, January, 2014,, 2014

Seismic micro hazard zonation for urban areas is the first step towards a seismic risk analysis and mitigation strategy. Essential here is to obtain a proper understanding of the local subsurface conditions and to evaluate ground shaking effects. In the present study, an attempt has been made to evaluate the seismic hazard considering local site effects by carrying out detailed geotechnical and geophysical site characterization in El-Fayoum New City. Seismic hazard analysis and microzonation of El-Fayoum New City are addressed in three parts: in the first part, estimation of seismic hazard is done using seismotectonic and geological information. Second part deals with site characterization using geotechnical and shallow geophysical techniques. In the last part, local site effects are assessed by carrying out one-dimensional (1-D) ground response analysis using equivalent linear method by program SHAKE 2000.

Journal of King Saud University - Science, 2010

Microtremor measurements are one of the most popular world-wide tool for estimation of site response especially within the urban area. This technique has been applied over 85 sites distributed regularly through Yanbu metropolitan area with an ultimate aim of seismic hazard microzonation for ground-shaking site effects. The horizontal to vertical spectral analysis (H/V) was carried out over all the sites to estimate both the fundamental resonance frequency and its corresponding amplification for the ground vibration. In most sites, H/V curve for amplitude spectra display a clear peak suggesting the presence of a soil-bedrock impedance contrast. Other sites, however, show more than one peak indicating the presence of more than one impedance contrast through sedimentary cover. The estimated values of fundamental frequency range from 0.25 Hz up to 7.9 Hz increases with decreasing depths of basement rock. It has lower values at the central zone extending from north to south compared to the eastern and western parts of Yanbu area. On the other hand, the estimated values of amplification factor ranges from the value of 2 to 5, where the higher values prevailing through the central zone with increasing thickness of sediments. Analyses of the acquired data set have clearly shown that, both of two parameters vary considerably through Yanbu city. This could be due to lateral variations in soil thickness and/or variations in the soil type at Yanbu area. These results show the 2D and 3D effect of basin geometry. The estimated values for the fundamental frequency from microtremor data are compared with that from shear-wave velocity structure within the area of interest and show an excellent agreement.

International Journal for Service Learning in Engineering, Humanitarian Engineering and Social Entrepreneurship

Many developing nations are situated in zones of high seismicity where earthquakes can lead to widespread property loss and loss of life. Similar-sized earthquakes are not nearly as devastating in developed nations because of access to state-of-practice engineering methods. Earthquake engineering to reduce property loss and loss of life includes geotechnical engineering to predict likely amounts of ground shaking. Herein, a simple geotechnical approach was implemented in four cities in northern Haiti, including Port-de-Paix, Cap-Haitien, Fort Liberte, and Ouanaminthe based. The approach was based on the use of a simple geophysical technique and the application of International Building Code criteria to calculate design levels of ground shaking. The Spectral-Analysis-of-Surface-Waves (SASW) method is a geophysical technique that was employed in the four test cities during a five-day test period utilizing three workers and a backpack full of equipment. As a result of this invest...

Journal of …, 2007

Two-dimensional shear wave velocity investigation using the multi-channel analysis of surface waves helps identify lateral and vertical variations of shear wave velocity at shallow depth. This information is required for predicting the ground motion response to earthquakes in areas underlain by thick soil cover. At one such area in Dehradun, at the foothills of the Himalaya, shear wave velocities of the near-surface soil were determined for 50 locations covering almost all representative units with respect to variation in local geology and geomorphology. Based on the average shear wave velocities of the upper 30 m of the soil, sites located in the south-southwestern and central part of the city are predominantly classified as class 'D' (180-360 m/s) except a few locations like Clement Town (site no. 43) and Majra (site no. 48), which can be classified as class 'E' due to very low shear wave velocity, in accordance with the NEHRP 1997 provision. The northern part of Dehradun city shows high velocities, ranging from 300 m/s at the surface to more than 700 m/s at depth of 30 m. These sites located in the northern and eastern parts of the city with average shear wave velocity (V S ) values more than 360 m/s have been classified as class 'C' site (360-760 m/s). The characteristic period estimated for each site of the soil column varies from 1.5 to 3.12 Hz. Based on the shear wave velocity, input motion, static and dynamic properties of different soil layers, siteresponse spectrum and amplification functions have been derived. The response spectrum suggests spectral acceleration value for two-storey structures of 3 to 8 times higher than the peak ground acceleration at the bed rock level, i.e. 0.05 g. The analysis also suggests peak amplification at 3-4, 2-2.5 and 1-1.5 Hz in the northern, central and south-southwestern parts of the city respectively.

eqrisk.info

Dehradun, besides being the capital, is one of the most densely populated cities in the state of Uttaranchal. Any future large earthquake in Himalaya is bound to affect the city's habitat. Site response is one of the basic parameter required by geotechnical engineers for carrying out the seismic microzonation to assess the seismic risk. Present study concentrates on estimating the dynamic response of various sites in Dehradun city so as to enable to predict the ground motion at these sites due to a future large earthquake. The Pear-shaped city was surveyed at a grid interval of approximately 2 km covering a total area of about 250 km2. Microtremor measurements were carried out at chosen locations for estimating the site effects. The reSonance frequencies and the amplification factors were estimated. The variations in soil thickness and soil types are reflected in the results. The results will improve as more data for weak motion is obtained at some representative sites.