Use of remote sensing and seismotectonic parameters for seismic hazard analysis of Bangalore

Deterministic Seismic Hazard Analysis (DSHA) for the Bangalore, India has been carried out by considering the past earthquakes, assumed subsurface fault rupture lengths and point source synthetic ground motion model. The sources have been identified using satellite remote sensing images and seismotectonic atlas map of India and relevant field studies. Maximum Credible Earthquake (MCE) has been determined by considering the regional seismotectonic activity in about 350 km radius around Bangalore. The seismotectonic map has been prepared by considering the faults, lineaments, shear zones in the area and past moderate earthquakes of more than 470 events having the moment magnitude of 3.5 and above. In addition, 1300 number of earthquake tremors having moment magnitude of less than 3.5 has been considered for the study. Shortest distance from the Bangalore to the different sources is measured and then Peak Horizontal Acceleration (PHA) is calculated for the different sources and moment magnitude of events using regional attenuation relation for peninsular India. Based on Wells and Coppersmith (1994) relationship, subsurface fault rupture length of about 3.8% of total length of the fault shown to be matching with past earthquake events in the area. To simulate synthetic ground motions, Boore (1983, 2003) SMSIM programs have been used and the PHA for the different locations is evaluated. From the above approaches, the PHA of 0.15 g was established. This value was obtained for a maximum credible earthquake having a moment magnitude of 5.1 for a source Mandya-Channapatna-Bangalore lineament. This particular source has been identified as a vulnerable source for Bangalore. From this study, it is very clear that Bangalore area can be described as seismically moderately active region. It is also recommended that southern part of Karnataka in particular Bangalore, Mandya and Kolar, need to be upgraded from current Indian Seismic Zone II to Seismic Zone III. Acceleration time history (ground motion) has been generated using synthetic earthquake model by considering the revised regional seismotectonic parameters. The rock level PHA map for Bangalore has been prepared and these maps are useful for the purpose of seismic microzonation, ground response analysis and design of important structures.

Magnitude Recurrence Relations for Colorado Earthquakes

Colorado has a significant potential for damaging earthquakes. The Colorado Geological Survey has identified 92 potentially active faults. Two faults have documented slip-rates approaching 1 mm per year. Four hundred and seventy-seven Colorado earthquakes have been felt and/or equaled or exceeded magnitude of 2.0 between 1870 and 1996. Eighty-two earthquakes have equaled or exceeded an MMI Scale of V. Colorado's largest historical earthquake, which occurred on 7 November 1882 (8 November UCT), had an estimated magnitude of 6.5 and maximum MMI of VII to VIII. Colorado's maximum credible earthquake has been estimated at 7.5 ML. In this paper we analyze independent earthquakes (foreshocks, aftershocks, and fluid-injection induced earthquakes removed) to develop magnitude-recurrence relations. Analysis of instrumentally measured earthquakes predicts that a 6.5 ML or larger earthquake occurring somewhere in Colorado has a mean recurrence interval of about 420 years. A magnitude 6.6 ML earthquake has a 10 percent Poisson's probability of exceedance in 50 years. A 7.5 ML earthquake has a 2 percent Poisson's probability of exceedance in 50 years. Colorado's magnitude-recurrence (Gutenberg-Richter) relation is log N=2.58−0.80 ML.

A More Rational Approach to Capacity Design of Seismic Moment Frame Columns

Inelastic time history analyses typically indicate that the traditional sub-assembly “capacity” approach used in the design of ductile moment frames grossly underestimates the maximum moments experienced by the columns during a maximum credible earthquake. In addition, these analyses predict that the maximum column demand moments often occur near the mid-height of concrete structures, whereas a conventional elastic analysis predicts maxima at the lowest levels of these structures. Incremental displacement analyses using modal properties and displacements predicted by a maximum credible response spectrum should be used to more accurately predict the maximum anticipated column demand moments in the analysis of existing structures or the design of new structures.