BITS Faculty Publications
Permanent URI for this communityhttp://localhost:4000/handle/123456789/1867
Browse
4 results
Search Results
Item Stochastic Modeling of Earthquake Interevent Counts (Natural Times) in Northwest Himalaya and Adjoining Regions(Springer, 2020-04) Pasari, SumantaIn the driven nonlinear complex dynamical earthquake system in which the event occurrences are distributed along a frequency-magnitude spectrum, “natural time” statistics can be utilized to evaluate the contemporary state of earthquake hazards in a region. The natural times, in contrary to the clock/calendar times, are nothing but the interspersed number of small magnitude counts between successive large earthquake events in a fixed area. Natural times are positive and often random in nature. In this paper, our aim is to investigate the best-fit probability distribution in order to develop natural time statistics in the seismogenic northwest Himalayan orogen including some part of north-central India, east-northeast Pakistan and its contiguous regions. We consider eight continuous probability distributions to fit the observed natural time data. We use maximum likelihood strategy for model parameter estimation and several goodness-of-fit measures for model prioritization. Results based on the natural times corresponding to M≥3 events between M≥6 events reveal that the exponential, exponentiated exponential, Weibull and exponentiated Weibull distributions provide the best fit to the observed natural times in the study area. In addition, assuming that the seismicity statistics of larger northwest Himalaya region is indifferent from the “local” regions (e.g., cities) embedded in the larger area, we calculate “nowcast” values for a number of cities, namely Jammu, Ludhiana, Chandigarh, Shimla, Dehradun and New Delhi, to assess the current state of earthquake hazards in these cities. It is found that their earthquake potential scores (%) are 99, 89, 86, 87, 83 and 58, respectively. From these results, we argue that the concept of natural times and thereby nowcasting technique provide a rapid, alternative and effective way to analyze earthquake hazards in a seismic region.Item Impact of directional effect of strong ground motion on scenario-based earthquake hazards: preliminary results(IOP, 2022) Pasari, SumantaScenario-based earthquake hazards are useful for social planning and disaster mitigation. In this study, general attenuation properties of earthquake events are analysed empirically with respect to the direction of seismic rupture from the epicentre. The study is primarily focused on presenting a relationship between fault source characteristics and the most credible direction of any earthquake that occurs at that source. Since such a direction is not only a function of source but also is dependent on site parameters, several ground motion prediction equations are utilised in congregation with methods to evaluate site parameters. The method involves a graphical relationship between scenario spectral ordinates and polar coordinates to estimate the most credible direction for that scenario. An analysis illustrating the method is presented here for the Himalayan megathrust fault, the Main Boundary Thrust.Item Impact of Three-Parameter Weibull Models in Probabilistic Assessment of Earthquake Hazards(Springer, 2013-08) Pasari, SumantaThis paper investigates the suitability of a three-parameter (scale, shape, and location) Weibull distribution in probabilistic assessment of earthquake hazards. The performance is also compared with two other popular models from same Weibull family, namely the two-parameter Weibull model and the inverse Weibull model. A complete and homogeneous earthquake catalog (Yadav et al. in Pure Appl Geophys 167:1331–1342, 2010) of 20 events (M ≥ 7.0), spanning the period 1846 to 1995 from north–east India and its surrounding region (20°–32°N and 87°–100°E), is used to perform this study. The model parameters are initially estimated from graphical plots and later confirmed from statistical estimations such as maximum likelihood estimation (MLE) and method of moments (MoM). The asymptotic variance–covariance matrix for the MLE estimated parameters is further calculated on the basis of the Fisher information matrix (FIM). The model suitability is appraised using different statistical goodness-of-fit tests. For the study area, the estimated conditional probability for an earthquake within a decade comes out to be very high (≥0.90) for an elapsed time of 18 years (i.e., 2013). The study also reveals that the use of location parameter provides more flexibility to the three-parameter Weibull model in comparison to the two-parameter Weibull model. Therefore, it is suggested that three-parameter Weibull model has high importance in empirical modeling of earthquake recurrence and seismic hazard assessment.Item Contemporary Earthquake Hazards in the West‐Northwest Himalaya: A Statistical Perspective through Natural Times(Geoscience, 2020-08) Pasari, SumantaHimalayan earthquakes have deep societal and economic impact. In this article, we implement a surrogate method of nowcasting (Rundle et al., 2016) to determine the current state of seismic hazard from large earthquakes in a dozen populous cities from India and Pakistan that belong to the west‐northwest part of Himalayan orogeny. For this, we (1) perform statistical inference of natural times, intersperse counts of small‐magnitude events between pairs of succeeding large events, based on a set of eight probability distributions; (2) compute earthquake potential score (EPS) of 14 cities from the best‐fit cumulative distribution of natural times; and (3) carry out a sensitivity testing of parameters—threshold magnitude and area of city region. Formulation of natural time (Varostos et al., 2005) based on frequency–magnitude power‐law statistics essentially avoids the daunting need of seismicity declustering in hazard estimation. A retrospective analysis of natural time counts corresponding to M≥6 events for the Indian cities provides an EPS (%) as New Delhi (56), Chandigarh (86), Dehradun (83), Jammu (99), Ludhiana (89), Moradabad (84), and Shimla (87), whereas the cities in Pakistan observe an EPS (%) as Islamabad (99), Faisalabad (88), Gujranwala (99), Lahore (89), Multan (98), Peshawar (38), and Rawalpindi (99). The estimated nowcast values that range from 38% to as high as 99% lead to a rapid yet useful ranking of cities in terms of their present progression to the regional earthquake cycle of magnitude ≥6.0 events. The analysis inevitably encourages scientists and engineers from governments and industry to join hands for better policymaking toward land‐use planning, insurance, and disaster preparation in the west‐northwest part of active Himalayan belt.