ABSTRACT Determining and verifying the limitations of commercially available programs for analyzing ground response are important, because inaccurate results will affect the inputs to the design response spectra of structures and thus... more
ABSTRACT Determining and verifying the limitations of commercially available programs for analyzing ground response are important, because inaccurate results will affect the inputs to the design response spectra of structures and thus inputs to building codes and the disaster mitigation process. Shake2000 is a Windows based computer program that is a variant of SHAKE which is one of the earliest and most successful computer codes that calculates the ground response. Although Shake2000 has been widely used for many years, there are not enough studies that reveal the usage limitations of SHAKE Shake2000 was used for the ground response analysis of Lalitpur, Nepal. A synthetic strong motion was used in the analysis for the worst case scenario; M=8, D=48km (hypocentral), amax=0.48g and resulted in maximum values of PGA=1.54g, and SA=2.799g for 3Hz frequency. For M=6.7, D=6.4km (epicentral), amax =0.5g record, maximum values were PGA=3.44g and SA=8.64g for 2Hz frequency. Although the reason for such high SA values could have been the use of stiff, thick soils and very severe earthquakes, further research revealed that when large magnitude earthquakes with high accelerations and stiff soils were simulated, SA values obtained were not reliability, such as 8.64g. In this study, it is demonstrated that the certainty of Shake2000 decreases when used with stiff soils and records with amax of 0.48 g and above.
The understanding of geotechnical characteristics of near-surface material is of fundamental interest in seismic microzonation. Shear wave velocity (Vs), one of the most important soil properties for soil response modeling, has been... more
The understanding of geotechnical characteristics of near-surface material is of fundamental interest in seismic microzonation. Shear wave velocity (Vs), one of the most important soil properties for soil response modeling, has been evaluated through seismic profiling using the multichannel analysis of surface waves in the city of Dehradun situated along the foothills of northwest Himalaya. Fifty sites in the city have been investigated with survey lines between 72 and 96 m in length. Multiple 1-D and interpolated 2-D profiles have been generated up to a depth of 30–40 m. The Vs were used in the SHAKE2000 software in combination with seismic input motion of the recent Chamoli earthquake to obtain site response and amplification spectra. The estimated Vs are higher in the northern part of the study area (i.e., 200–700 m/s from the surface to a depth of about 30 m) as compared to the south and southwestern parts of the city (i.e., 180–400 m/s for the same depth range). The response spectra suggest that spectral acceleration values for two-story structures are three to eight times higher than peak ground acceleration at bedrock. 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. The spatial distributions of Vs and spectral accelerations provide valuable information for the seismic microzonation in different parts of the urban area of Dehradun.
3D terrestrial laser scanning is a relatively new, but already revolutionary, surveying technique. The survey yield a digital data set, which is essentially a dense “point cloud”, where each point is represented by a coordinate in 3D... more
3D terrestrial laser scanning is a relatively new, but already revolutionary, surveying technique. The survey yield a digital data set, which is essentially a dense “point cloud”, where each point is represented by a coordinate in 3D space. The most important advantage of the method is that a very high point density can be achieved, in the order of 5 to 10 mm resolution. In order to analyse the character and shape of the scanned surfaces it is necessary to convert the irregularly distributed point data into 3D surface information using surface reconstruction. The reconstructed surface can subsequently be visualized using a variety of 3D visualization techniques. From the reconstructed 3D surfaces, it is also possible to generate 2D profiles or elevation contour lines for use in regular GIS or CAD packages. A number of applications are described in this paper, which may illustrate the possible benefits of using laser scanning as a technique in engineering geological practice and research: volume analysis and monitoring, detailed and large-scale topographic mapping, tunnelling, rock face surveying, and digital outcrop mapping.
3D terrestrial laser scanning is a relatively new, but already revolutionary, surveying technique. The survey yield a digital data set, which is essentially a dense point cloud, where each point is represented by a coordinate in 3D space.... more
3D terrestrial laser scanning is a relatively new, but already revolutionary, surveying technique. The survey yield a digital data set, which is essentially a dense point cloud, where each point is represented by a coordinate in 3D space. The most important advantage of the method is that a very high point density can be achieved, in the order of 5 to 10 mm resolution. In order to analyse the character and shape of the scanned surfaces it is necessary to convert the irregularly distributed point data into 3D surface information using surface reconstruction. The reconstructed surface can subsequently be visualized using a variety of 3D visualization techniques. From the reconstructed 3D surfaces, it is also possible to generate 2D profiles or elevation contour lines for use in regular GIS or CAD packages. A number of applications are described in this paper, which may illustrate the possible benefits of using laser scanning as a technique in engineering geological practice and research: volume analysis and monitoring, detailed and large-scale topographic mapping, tunnelling, rock face surveying, and digital outcrop mapping.
The research investigates the possibility of using point cloud data from 3-D terrestrial laser scanning as a basis to characterise discontinuities in exposed rock massed in an automated way. Examples of discontinuities in rock are bedding... more
The research investigates the possibility of using point cloud data from 3-D terrestrial laser scanning as a basis to characterise discontinuities in exposed rock massed in an automated way. Examples of discontinuities in rock are bedding planes, joints, fractures and schistocity. The characterisation of discontinuities is of importance, since they determine to a large extend the geotechnical behaviour of the entire rock mass. The conventional way of characterising discontinuities is by manual geological survey using geological compass and measuring tape. A logical alternative to the conventional methods for surveying rock faces is the use of 3-D terrestrial laser scanning. A 3-D terrestrial laser scanning survey yield a 3-D point cloud but this data does not yet provide the information on the character of the discontinuities that can be seen in the rock exposure. In this research two different approaches are followed: the first approach uses surface reconstruction through interpolation of the point cloud and the second approach makes use of direct segmentation of the original point cloud. The main conclusion of this research is that it is possible to automate the derivation of discontinuity orientation and spacing information with both methods. Point cloud segmentation is however, the most preferred approach, since it does not require prior surface reconstruction, is therefore faster, and is not strongly influenced by vegetation and other noise in the data. Point cloud segmentation uses the original point cloud, so there is no data loss, which is unavoidable with a surface reconstruction approach.
Until recently, the Aswa lineament shear zone in Uganda and Sudan was considered to be tectonically at rest but the 1990- 1991 seismic events triggered a renewal of interest in this area. Using ERS1 - ERS2 tandem covering the area where... more
Until recently, the Aswa lineament shear zone in Uganda and Sudan was considered to be tectonically at rest but the 1990- 1991 seismic events triggered a renewal of interest in this area. Using ERS1 - ERS2 tandem covering the area where earthquakes were observed, we have generated a high resolution Digital Elevation Model (DEM) which provides a good quality reference to analyze the geomorphology and the drainage patterns, in order to extract valuable tectonic information. Then, the combination of spaceborne radar interferometry and Landsat TM imagery contributes to a better understanding of the geological and tectonic phenomena of the studied area.
One of the 22 active volcanoes in the Philippines is Mt. Bulusan. The volcano erupted more than 15 times recent history, but the majority of these eruptions were mild phreatic eruptions. Field evidence shows however that Bulusan is... more
One of the 22 active volcanoes in the Philippines is Mt. Bulusan. The volcano erupted more than 15 times recent history, but the majority of these eruptions were mild phreatic eruptions. Field evidence shows however that Bulusan is capable of producing lava flows, domes, pyroclastic currents and lahars. Bulusan therefore poses a potentially major risk to the dense population at the footslopes of the volcano. Hence the volcano is constantly monitored with seismic equipment. To mitigate the potential hazards posed by this volcano, a volcanic hazard mapping program has been undertaken. Because of lacking existing geological and geographical data, it was decided to use optical and radar remote sensing techniques to acquire additional data. A GIS database was created at a medium scale, which was used as a reference for the development of preliminary hazard maps for each of the volcanic hazards that have been identified. An elementary approach, making use of the 'Energy cone' concept, was followed to outline the areas subject to potential pyroclastic flows and surges. Lava- and lahar flow path predictions were made based on the Digital Terrain Model (DTM).
In this study, 3D terrestrial laser scan data have been used to quantify the surface roughness of rock mass discontinuities, to determine the roughness scale effect and to determine the influence of the range of precision. The... more
In this study, 3D terrestrial laser scan data have been used to quantify the surface roughness of rock mass discontinuities, to determine the roughness scale effect and to determine the influence of the range of precision. The Roughness-length method was applied to calculate fractal parameters (fractal dimension and roughness amplitude). The study showed that it is possible to calculate the fractal parameters from laser scan data of discontinuity surfaces. It has been found that the fractal dimension and roughness amplitude are very high for raw laser scan data, due to range measurement error of the used scanner. The discontinuity surface has been reconstructed from the raw point data using a scattered data interpolation technique. The range measurement error can be removed using this data interpolation technique. The reconstructed surface visually resembles the actual discontinuity surface. The fractal parameters of the reconstructed surface have subsequently been calculated. By subtracting the fractal parameters of the raw data from the fractal parameters of the reconstructed surface, the range error of the laser scan data can be estimated. The fractal parameters have also been calculated using different sample sizes. The fractal parameters show an increase with increasing sample size. This means that the roughness complexity of the discontinuity surface is also increasing with increasing sample size. From this observation it can be concluded that the roughness of discontinuity surfaces has a significant scale effect. The maximum resolution of the laser scan data used in this study is 5 mm (1 point per 5 mm). The laser scan data with 5 mm resolution can only acquire roughness information from roughness features larger than 5 mm. Consequently, small-scale roughness (roughness features smaller than 5 mm) can not be obtained from the data. Therefore the resolution of the laser scan data (point density) needs to be increased to quantify discontinuity surface roughness accurately as a smaller scale.
For the induced seismicity in the province of Groningen in the Netherlands, Ground Motion Prediction Equations (GMPE) are integrated with seismic hazard models into Ground Motion Models (GMM). These models are used as earthquake intensity... more
For the induced seismicity in the province of Groningen in the Netherlands, Ground Motion Prediction Equations (GMPE) are integrated with seismic hazard models into Ground Motion Models (GMM). These models are used as earthquake intensity measure predictors for building damage assessments and structural upgrading or design. The GMM and GMPE relations can account for deep and shallow geology, but do not account explicitly for local geometrical or topographic effects and anthropogenic soils. Canals and artificial dwelling hills are local conditions that could possibly influence ground motion intensity and/or increase building damage potential. In this study the effect of both artificial dwelling hills and canals on dynamic ground response is evaluated by a set of linear elastic dynamic numerical analyses with the finite element code PLAXIS 2D. Different typical scenarios regarding geometrical features and soil conditions are defined and five past recorded earthquake signals from the a...
