Utpal Dutta - Academia.edu (original) (raw)

Papers by Utpal Dutta

The Indian journal of medical research, 1998

Fifty one patients with acute lymphoblastic leukaemia (ALL) and non-Hodgkins lymphoma (NHL) under... more Fifty one patients with acute lymphoblastic leukaemia (ALL) and non-Hodgkins lymphoma (NHL) undergoing chemotherapy were studied prospectively to determine the incidence, aetiology and natural course of hepatitis. Of 51 patients (31 NHL and 20 ALL), 22 developed hepatitis. Hepatitis B (IgM anti HBc positive) was the cause in 11 patients (50%), hepatitis C in 4 patients, and septicaemia and cytotoxic drugs in 3 patients each. Malignant infiltration of the liver was the cause in the remaining 1 patient. Hepatitis was predominantly (75%) anicteric. Mean duration of hepatitis was 21 days. Of 51 patients, 21 acquired hepatitis B and/or C virus infection. They had received 6.4 (+/- 3.4) units of packed red cells and 5.3 (+/- 11) units of platelet concentrate as compared to 3.4 (+/- 4.8) units of red cells and 5.3 (+/- 12.1) units of platelet concentrate received by those who did not acquire virus infection (P < 0.05 for packed red cells). Only transient stoppage of chemotherapy was nec...

14 th World Conference …, 2008

We are generating physically plausible near-field synthetic ground motions for the Great 1964 Pri... more We are generating physically plausible near-field synthetic ground motions for the Great 1964 Prince William Sound, Alaska, earthquake compatible with available seismological data, tectonic information and eyewitness accounts. The objectives of this study are summarized as follows: (a) Simulation of the low-frequency (f < 0.03Hz) strong ground motions on selected locations and on a dense grid of observation points extending over the shallow dipping causative fault of the 1964 Alaska earthquake. In order to accomplish this task, we are utilizing the slip model proposed by Johnson et al. (1996) based on a joint inversion of tsunami waveforms and geodetic data. The calculations are carried out using the discrete wavenumber representation method and the generalized transmission and reflection coefficient technique; (b) Reconstruction of the strong ground motion time histories and response spectra that the city of Anchorage experienced during the 1964 Alaska earthquake. The low-frequency (f < 0.03Hz) ground motions are generated using the methodology described previously. The intermediate-frequency (0.03Hz < f < 0.50Hz) ground motions are simulated by convolving Green's functions generated by the discrete wavenumber representation method with far-field radiation pulses of circular cracks. The high-frequency (0.5Hz < f < 8.0Hz) ground motions are simulated using the stochastic modeling approach. The three independently derived ground motion components are then properly combined to generate synthetic broadband ground motion time histories and response spectra for the city of Anchorage due to the 1964 Prince William Sound earthquake; and (c) Validation of the synthetic strong ground motions for the 1964 Alaska earthquake against observed tectonic deformation, ground motion estimates inferred by descriptions of structural damage, and eyewitness accounts. In summary, the present study provides synthetic time histories and response spectra for engineering applications compatible with all available information pertaining to the 1964 Prince William Sound earthquake. It should be noted however that the generated strong ground motions are not necessarily unique, nor reflect the entire uncertainty that characterizes the problem under investigation.

Pure and Applied Geophysics, 2022

Anchorage, Alaska, is located in one of the most active tectonic settings in the world. The city ... more Anchorage, Alaska, is located in one of the most active tectonic settings in the world. The city and region were significantly impacted by the MW 9.2 Great Alaska Earthquake in 1964, and they were recently shaken by a MW 7.1 event in 2018. The city was developed in an area underlain by complex soil deposits of varied geological origins and stiffnesses, with the deposits’ thicknesses increasing east to west. Situated at the edge of the North American Plate, with the actively subducting Pacific Plate below, Anchorage is susceptible to both intraslab and interface earthquakes, along with crustal earthquakes. Strong-motion stations were installed across the city in an attempt to capture the variability in site response. Several previous studies have been performed to evaluate that variability but have not included larger magnitude events and have not benefited from the current density of instrumentation. The work presented here provides background information on the geology and tectonic...

Soil Dynamics and Earthquake Engineering, 2021

The use of horizontal to vertical spectral ratios (HVSR) of earthquake ground motions has become ... more The use of horizontal to vertical spectral ratios (HVSR) of earthquake ground motions has become a standard technique to characterize sites, especially those lacking subsurface measurements. Several studies have developed relationships between HVSR results and time-averaged shear-wave velocity in the upper 30m (VS30). Other studies have utilized standard spectral ratios calculated from horizontal ground motion Fourier amplitude spectra to estimate VS30. Anchorage, Alaska (USA), has a network of strong-motion recording stations, many of which have no site-specific subsurface characterization. This study compares measured VS30 and HVSR results from 18 strong-motion stations to four regional models developed by others. A relationship between the 1 Hz band-averaged (0.5 to 2.5 Hz) spectral amplification results and VS30 is presented. VS30 estimates for the strong-motion stations are made, and a regional model is developed between HVSR and VS30, both in terms of fpeak (the frequency of the peak HVSR amplitude) and Apeak (the amplitude of the peak). In addition to the regional model, additional VS30 data from other sites in Anchorage, including 19 downhole VS30 measurements and 22 microtremor VS30 estimates from others, are used with the strong-motion station VS30 estimates to develop a VS30 contour map of Anchorage. The contouring represents the spatial distribution of the site classes of the local building code, which are based on VS30. This map may be incorporated into planning documents for future developments in the city.

Conventional soil models with single spring and damping components can not properly simulate the ... more Conventional soil models with single spring and damping components can not properly simulate the frequency-dependent behavior of foundation soils. In this study, the foundation soil is modeled by a two-degrees-of-freedom mechanical model (2DOF) with eight integrated constant parameters. The 2DOF model provides a reasonable basis for the nonlinear dynamic analysis of soil-structure interaction (SSI) system in the time domain. To determine the values of the integrated parameters in the 2DOF model, a system identification technique using the extended Kalman filter (EKF) is developed in this study. To improve the computational accuracy and simplicity, the first order polynomial approximation is applied in the EKF procedure. A realistic identification example is given for two soil sites in Anchorage, Alaska. The recorded seismic data from two relatively long-period earthquakes, the Nanana earthquake (23rd October 2002) and the Denali earthquake (3rd November 2002), are used for the ident...

This document is disseminated under the sponsorship of the U.S. Department of Transportation in t... more This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document. Quality Assurance Statement The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement. Author's Disclaimer Opinions and conclusions expressed or implied in the report are those of the author. They are not necessarily those of the Alaska DOT&PF or funding agencies.

Geophysical Journal International, 2000

High-frequency Rayleigh waves were generated in the frequency range of about 1±100 Hz by an elect... more High-frequency Rayleigh waves were generated in the frequency range of about 1±100 Hz by an electromagnetic vibrator in cooperation with the Vibration Instrument Company, Japan, and the Ensol Corporation, North Carolina, at 36 sites in Anchorage. From phase delay times between two sensors, the phase velocity of the fundamental mode at each site was computed. These data were inverted in terms of shear wave velocity structure by a stochastic inversion scheme. Of the 36 sites, values of shear wave velocity (b) as a function of depth were available at seven sites from downhole measurements. At these sites, the comparison of the results obtained by others between surface and downhole measurements showed reasonable agreement. These results were therefore combined with those of the remaining 29 sites obtained in this study. The b structure of the 36 sites could be subdivided into four groups. On the basis of NEHRP provision and from the time-averaged b structures for the uppermost 30 m corresponding to the four groups, it has been possible to identify the lateral extent of soil classes C and D in the Anchorage area. From statistical analysis of the time-averaged b data, it is shown that the lithology of the area in soil class C is distinct from that in D. The same is true for the subunits, namely, glacio¯uvial deposits in areas of C and D. Moreover, the areas in soil class D along the Knik Arm in west Anchorage with relatively low b-values coincide with the areas of high ground failure susceptibility identi®ed by others from observations following the Prince William Sound earthquake (M w =9.2) of 1964.

Bulletin of the Seismological Society of America, 2009

This study deals with shallow sedimentary structure of the Anchorage basin in Alaska. For this pu... more This study deals with shallow sedimentary structure of the Anchorage basin in Alaska. For this purpose, inversion of site response [SRf] data in the frequency range 0.5-11.0 Hz from various sites of the basin has been performed using the simulated annealing method to compute subsurface layer thickness, shear-wave velocity (β), density, and shear-wave quality factor. The one-dimensional (1D) models for the aforementioned parameters were obtained with preset bounds on the basis of available geological information such that the L-2 norm error between the observed and computed site response attained a global minimum. Next, the spatial distribution of the important parameter β was obtained by interpolating values yielded by the 1D models. The results indicate the presence of three distinct velocity zones as the source of spatial variation of SRf in the Anchorage basin. In the uppermost part of the basin, the β values of fine-grain Quaternary sediments mainly lie in the range of 180-500 m=sec with thickness varying from 15 to 50 m. This formation overlies relatively thick (80-200 m) coarse-grain Quaternary sediments with β values in the range of 600-900 m=sec. These two Quaternary units are, in turn, overlain on Tertiary sediments with β > 1000 m=sec located at depths of 100 and 250 m, respectively, in the central and western side along the Knik Arm parts of the basin. The important implication of the result is that the sources of spatial variation of SRf in the Anchorage basin for the frequency band 0.5-11 Hz, besides in the uppermost 30 m, are found to be deeper than this depth. Thus, use of commonly considered geological formations in the depth intervals from 0 to 30 m for the ground-motion interpretation will likely yield erroneous results in the Anchorage basin.

A novel velocity estimation algorithm that will be developed and applied that incorporates the co... more A novel velocity estimation algorithm that will be developed and applied that incorporates the constraints of three seismic functionals: Receiver functions, waveform modeling, and surface wave dispersion measurements. These functionals have distinct but complementary sensitivities to Earth structure and have all been employed in modeling studies previously, yet each fails to resolve ambiguities between realistic models when used alone. By incorporating constraints from all three functionals we can minimize the part of the model space for which data constraints fail to distinguish between models. While several recent studies attempt to model two of these functionals jointly, none explores or assesses adequately the improvements in model reliability that are gained by incorporating additional constraints. The general search techniques and assessment tools we will employ allow us to describe the size and characteristics of the acceptable model space, proscribe the set of unacceptable models, and identify characteristics that are required by the data, rather than those that are simply consistent with the data. As a result, the method will quantitatively evaluate the strengths of the constraints imposed by each data functional on each model parameter. The Bayesian formulation we propose provides a formal mechanism for incorporating the results of one inversion (as a "prior") into the inversion of a second type, to produce a multi-step "joint" (as opposed to "simultaneous") modeling procedure. The final results will be models that are accompanied by detailed, quantitative assessments of model reliability. In addition, these tools will guide us toward the types and characteristics of additional data that should be sought in order to improve model constraints and, therefore, model reliability. Another benefit of the proposed modeling method is that it will allow seismologists to produce models for relatively aseismic regions of the world, where station density is sparse, and where, for example, one particular data functional is rarely observed. It will therefore result in a method that is more broadly applicable than methods that rely upon one data functional alone. Lastly, numerous areas have been studied with "campaign"-style temporary deployments, which often produce a relatively small dataset compared to permanent stations. Broadening the range of data types employed in modeling will generally produce more reliable models for sparsely sampled regions. We will ultimately apply our modeling to stations in the Middle East. Besides being an area of monitoring interest, the Middle East is tectonically complex. As such, it is a region where fitting multiple datasets can choose among various non-unique models, as well as reconcile seemingly inconsistent data.

Geophysical Journal International, 2004

Bulletin of the Seismological Society of America, 2011

The generalized inversion of S-wave spectral amplitude data from 18 strong-motion sites in the Ka... more The generalized inversion of S-wave spectral amplitude data from 18 strong-motion sites in the Kachchh seismic zone, Gujarat, India, has been carried out to estimate source parameters of 38 aftershocks (M w 2.93-5.32) from the 2001 Bhuj earthquake (M w 7.7). The result shows that the seismic moment M 0 and source radius r of aftershocks are between 3:1 × 10 13 and 2:0 × 10 17 N•m and 226-889 m, respectively, while stress drops (Δσ) vary from 0.11 to 7.44 MPa. The regression analysis between M 0 and r shows a break in linear scaling at M 0 10 15:30 N•m. The estimated stress-drop values scatter significantly with M 0 (Δσ ∝ M 0:5-1 0) for larger aftershocks (M 0 ≥ 10 15:30 N•m) but vary in proportion with M 0 (Δσ ∝ M 3 0) in case of smaller magnitude events. This can be due to the complex rupture process associated with relatively larger aftershocks in comparison to circular rupture for smaller events. The high stress-drop values are observed for events located on the north Wagad fault (at 15-30 km depths) and Gedi fault (at 0-5 km depths). This could be attributed to the large stress develop at the hypocentral depth as a result of high pore-fluid pressure beneath these two fault zones. The regression between M 0 and corner frequency f c shows M 0 is proportional to f 5:84 c , which is consistent for earthquakes with short rupture lengths and high stress-drop values. High stress-drop values commonly associated with the events from Kachchh and adjacent Narmada-Son lineament rift zones indicate strong potential for generating high peak ground accelerations and hence high seismic hazard.

Geophysical Journal International, 2015

Seismic velocity models are found, along with uncertainty estimates, for 11 sites in the Middle E... more Seismic velocity models are found, along with uncertainty estimates, for 11 sites in the Middle East by jointly modelling Ps and Sp receiver functions and surface (Rayleigh) wave group velocity dispersion. The approach performs a search for models that satisfy goodness-of-fit criteria guided by a variant of simulated annealing and uses statistical tools to assess these products of searches. These tools, a parameter correlation matrix and marginal posterior probability density (PPD) function, allow us to evaluate quantitatively the constraints that each data type imposes on model parameters and to identify portions of each model that are well-constrained relative to other portions. This joint modelling technique, which we call 'multi-objective optimization for seismology', does not require a good starting solution, although such a model can be incorporated easily, if available, and can reduce the computation time significantly. Applying the process described above to broadband seismic data reveals that crustal thickness varies from 15 km beneath Djibouti (station ATD) to 45 km beneath Saudi Arabia (station RAYN). A pronounced low velocity zone for both Vp and Vs is present at a depth of ∼12 km beneath station KIV located in northern part of greater Caucasus, which may be due to the presence of a relatively young volcano. Similarly, we also noticed a 6-kmthick low velocity zone for Vp beginning at 20 km depth beneath seismic station AGIN, on the Anatolian plateau, while positive velocity gradients prevail elsewhere in eastern Turkey. Beneath station CSS, located in Cyprus, an anomalously slow layer is found in the uppermost mantle, which may indicate the presence of altered lithospheric material. Crustal P-and S-wave velocities beneath station D2, located in the northeastern portion of central Zagros, range between 5.2-6.2 and 3.2-3.8 km s −1 , respectively. In Oman, we find a Moho depth of 34.0 ± 1.0 km and 25.0 ± 1.0 to 30.0 ± 1.0 km beneath stations S02 and S04, respectively.

The paper presents waveform inversion technique using the local earthquake data to estimate the c... more The paper presents waveform inversion technique using the local earthquake data to estimate the crustal structure of the Anchorage basin, Alaska. Three component recorded data of an earthquake (M L = 4.8) from 26 strong motion station sites in Anchorage area are used for this purpose. The technique uses parallelized reflectivity method to compute synthetic seismograms of SH-, SV-, and P-wave motions and implements global optimization technique based on simulated annealing inversion to fit the observed waveform data with the computed seismograms. The inversion searches for optimal values of four model parameters namely the layer thickness, P-wave velocity, P to Swave velocity ratio and density at each site. The inversion shows that the crustal thickness of the Anchorage basin is around 40 km with P-and S-wave velocity at the bottom of the crust is around 6.4 km/s and 3.8 km/s, respectively. It is noticed that the observed ground motions of the Anchorage basin are strongly affected by the S-wave velocities of the shallow (< 0.1 km) sediments. The P-wave amplification due to the basin sediments is not significant. The presence of low S-wave velocity zones primarily responsible for the observed variations of the ground motions characteristics within the Anchorage basin. The P-to-S-wave velocity ratio varies from 10.0 to 2.0 for the shallower parts of the basin and remains around 1.78 in the deeper parts of the basin.