
 The spectral ratio between horizontal and vertical components (H/V ratio) of microtremors measured at the ground surface has been used to estimate fundamental periods and amplification factors of a site, although this technique lacks theoretical background. The aim of this article is to formulate the H/V technique in terms of the characteristics of Rayleigh and Love waves, and to contribute to improve the technique. The improvement includes use of not only peaks but also troughs in the H/V ratio for reliable estimation of the period and use of a newly proposed smoothing function for better estimation of the amplification factor. The formulation leads to a simple formula for the amplification factor expressed with the H/V ratio. With microtremor data measured at 546 junior high schools in 23 wards of Tokyo, the improved technique is applied to mapping site periods and amplification factors in the area.

Ground Motion Characteristics Estimated from Spectral Ratio between Horizontal and Verticcl Components of Mietremors.

The purpose of this investigation was to identify and quantify the effect of numerous variables on the performance of fiber-stabilized sand specimens. Laboratory unconfined compression tests were conducted on sand specimens reinforced with randomly oriented discrete fibers to isolate the effect of each variable on the performance of the fiber-reinforced material. Five primary conclusions were obtained from this investigation. First, the inclusion of randomly oriented discrete fibers significantly improved the unconfined compressive strength of sands. Second, an optimum fiber length of 51 mm (2 in.) was identified for the reinforcement of sand specimens. Third, a maximum performance was achieved at a fiber dosage rate between 0.6 and 1.0% dry weight. Fourth, specimen performance was enhanced in both wet and dry of optimum conditions. Finally, the inclusion of up to 8% of silt does not affect the performance of the fiber reinforcement.

Closure of "Engineering Properties of Sand-Fiber Mixtures for Road Construction"

A procedure for estimating ground motions using recorded accelerograms is described. The premise of the study is the assumption that future ground motions will be similar to those observed for similar site and tectonic situations in the past. Direct techniques for scaling existing accelerograms have been developed, based on relative estimates of local magnitude,M

 L
 . Design events are described deterministically in terms of fault dimension, tectonic setting (stress drop), fault distance, and site conditions. A combination of empirical and theoretical arguments is used to develop relationships betweenM

 L
 and other earthquake magnitude scales. In order to minimize scaling errors due to lack of understanding of the physics of strong ground motion, the procedure employs as few intermediate scaling laws as possible. The procedure conserves a meaningful measure of the uncertainty inherent when predicting ground motions from simple parameterizations of earthquake sources and site conditions.

Estimating ground motions using recorded accelerograms

In Southern California the conventional method for evaluating surficial stability has a bias towards cohesion. It suggests that surficial failures are more likely in slopes made of sandy and gravelly soils, than those composed of clays and silts. This contradicts actual observations. A study of the equations governing seepage and rainfall data in Southern California suggests that permeability plays an important role in the surficial stability of slopes. In homogeneous slopes this study finds that soils with a low permeability are more prone to develop the conditions leading to a surficial failure mechanism. Hence, clayey and silty soils slopes are more prone to develop surficial instability than slopes made of sandy or gravelly soils. This study also finds that soils with a permeability greater than a certain limiting value, klim, will not become saturated. It is found that the Unified Soil Classification System is useful in evaluating the likelihood that a surficial failure mechanism with seepage paralle...

Effect of permeability on surficial stability of homogeneous slopes. closure

우리나라의 流行性耳下腺炎에 關한 血淸學的 調査硏究 (1970)

Earthquakes are known to have occurred in Indian subcontinent from ancient times. This paper presents the results of seismic hazard analysis of India (6 degrees-38 degrees N and 68 degrees-98 degrees E) based on the deterministic approach using latest seismicity data (up to 2010). The hazard analysis was done using two different source models (linear sources and point sources) and 12 well recognized attenuation relations considering varied tectonic provinces in the region. The earthquake data obtained from different sources were homogenized and declustered and a total of 27,146 earthquakes of moment magnitude 4 and above were listed in the study area. The sesismotectonic map of the study area was prepared by considering the faults, lineaments and the shear zones which are associated with earthquakes of magnitude 4 and above. A new program was developed in MATLAB for smoothing of the point sources. For assessing the seismic hazard, the study area was divided into small grids of size 0.1 degrees x 0.1 degrees (approximately 10 x 10 km), and the hazard parameters were calculated at the center of each of these grid cells by considering all the seismic sources within a radius of 300 to 400 km. Rock level peak horizontal acceleration (PHA) and spectral accelerations for periods 0.1 and 1 s have been calculated for all the grid points with a deterministic approach using a code written in MATLAB. Epistemic uncertainty in hazard definition has been tackled within a logic-tree framework considering two types of sources and three attenuation models for each grid point. The hazard evaluation without logic tree approach also has been done for comparison of the results. The contour maps showing the spatial variation of hazard values are presented in the paper.

/pdf/deterministic-seismic-hazard-macrozonation-of-india-1kwhrnjdo4.pdf

Deterministic seismic hazard macrozonation of India

This paper presents spatial variation of seismic hazard at the surface level for India, covering 6–38° N and 68–98° E. The most recent knowledge on seismic activity in the region has been used to evaluate the hazard incorporating uncertainties associated with the seismicity parameters using different modeling methodologies. Three types of seismic source models, viz. linear sources, gridded seismicity model and areal sources, were considered to model the seismic sources and different sets of ground motion prediction equations were used for different tectonic provinces to characterize the attenuation properties. The hazard estimation at bedrock level has been carried out using probabilistic approach and the results obtained from various methodologies were combined in a logic tree framework. The seismic site characterization of India was done using topographic slope map derived from Digital Elevation Model data. This paper presents estimation of the hazard at surface level, using appropriate site amplification factors corresponding to various site classes based on V S30 values derived from the topographic gradient. Spatial variation of surface level peak horizontal acceleration (PHA) for return periods of 475 years and 2475 years are presented as contour maps.

Probabilistic assessment of surface level seismic hazard in India using topographic gradient as a proxy for site condition

Online material : Earthquake catalog; coordinates of source zones; list of events in each zone; frequency magnitude distribution plots.

Identification and characterization of seismic sources are essential input for seismic hazard analysis. A complete and consistent catalog of earthquakes in a region can offer good data for studying the distribution of earthquakes with respect to space, time, and magnitude. Earthquakes are known to have occurred in the region of the Indian subcontinent from historic times. Most of the activities, including many great earthquakes, have occurred in the northern subcontinent and in the Andaman and Nicobar regions. In the southern peninsula, damaging earthquakes have occurred, but their frequency was less and magnitudes were lower than the plate boundary earthquakes. The tectonic framework of the Indian subcontinent—an area of about 3.2 million square kilometers—is complex and varied spatially. This necessitates identifying different regions of similar seismicity. In this study we attempt to identify and characterize regional seismic source zones based on a homogeneous catalog of earthquakes in and around India from 250 BC until 2010. We identified different regional seismic source zones and created separate catalogs for each respective zone.

Most earthquake catalogs do not report earthquake magnitudes consistently over time, which may hinder defining seismicity patterns or assessing seismic hazards. The magnitude scales used for earthquake catalogs in India are not homogeneous. Compiling a complete catalog of earthquakes with uniform magnitudes is essential for defining seismicity patterns and assessing seismic hazards for a region (Chen and Tsai 2008). Hence the original magnitudes of earthquakes have to be converted to a common and reliable magnitude scale using appropriate magnitude correlations. In the raw catalog, many events can be dependent events that occurred in association with a mainshock in a cluster. These aftershocks and foreshocks have to be removed from the catalog using …

Characterization of Regional Seismic Source Zones in and around India

Seismic hazard analysis of India using areal sources

An attempt has been made to quantify the variability in the seismic activity rate
across the whole of India and adjoining areas (0–45°N and 60–105°E) using earthquake
database compiled from various sources. Both historical and instrumental data were
compiled and the complete catalog of Indian earthquakes till 2010 has been prepared.
Region-specific earthquake magnitude scaling relations correlating different magnitude
scales were achieved to develop a homogenous earthquake catalog for the region in unified
moment magnitude scale. The dependent events (75.3%) in the raw catalog have been
removed and the effect of aftershocks on the variation of b value has been quantified. The
study area was divided into 2,025 grid points (1°91°) and the spatial variation of the
seismicity across the region have been analyzed considering all the events within 300 km
radius from each grid point. A significant decrease in seismic b value was seen when
declustered catalog was used which illustrates that a larger proportion of dependent events
in the earthquake catalog are related to lower magnitude events. A list of 203,448 earth-
quakes (including aftershocks and foreshocks) occurred in the region covering the period
from 250 B.C. to 2010 A.D. with all available details is uploaded in the website
http://www.civil.iisc.ernet.in/*sreevals/resource.htm.

Sreevalsa Kolathayar

Papers

Deterministic seismic hazard macrozonation of India

Probabilistic assessment of surface level seismic hazard in India using topographic gradient as a proxy for site condition

Characterization of Regional Seismic Source Zones in and around India

Seismic hazard analysis of India using areal sources

Spatial variation of seismicity parameters across India and adjoining areas