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Typical example of the SH component of velocity time history of an earthquake recorded at Sikandra station of the Koldam network. The acceleration and displacement spectra along with the fitted source model are shown by the blue line
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The Koldam site falls in the Himachal Lesser Himalaya in the vicinity of the Main Boundary Thrust. The Main Central Thrust is located about 80 km northeast of the dam site. The region around Koldam site is marked by the occurrence of moderate to large-sized earthquakes. In this study, hypocenter parameters and source parameters of 70 local events (...
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Context 1
... has been applied. From the corrected source spectrum, the values of spectral parame- ters, viz., Ω 0 , f c , and f max , were estimated. For this purpose, the software EQK_SRC_PARA ( Kumar et al. 2012) has been adopted. A typical example of the time series of a local earthquake, along with the estimated and modeled source spectra, is shown in Fig. ...
Context 2
... data set of 70 local events recorded on three-component broadband seismometers at SKND station with a sampling rate of 100 samples per second from January 2009 to October 2010 has been used to estimate the source parameters. The digital time series of local events have been corrected for baseline correction and for instrument re- sponse. For path correction, a frequency-dependent attenuation relation, Q c = 110 f 1.02 (Gupta and Kumar 2002), developed for the Garhwal Himalayan region from coda waves of local earthquakes, has been applied. From the corrected source spectrum, the values of spectral parameters, viz., Ω 0 , f c , and f max , were estimated. For this purpose, the software EQK_SRC_PARA (Kumar et al. 2012) has been adopted. A typical example of the time series of a local earthquake, along with the estimated and modeled source spectra, is shown in Fig. 2. Following Kellis-Borok (1959), the seismic moment is estimated from the value of Ω ...
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Citations
... Abercombie and Leary (1993); Zobin and Hasakov (1995) and several others are notable recent contributors in the field of source parameter studies in different parts of the world. In Himalayan region various researchers (e.g., Singh et al., 1979;Wason, 1994, 1995;Kumar et al., 2006;2012;2013a, b, c;2014a, c;Paidi et al., 2013) have calculated source parameters for Himalayan and nearby regions. To the best of authors' knowledge, the source parameter studies using broadband data have not been carried out in Nubra Region, India so far. ...
The digital time histories of local earthquake data recorded during January 2010 to February 2011 by a local network of broad band seismographs in Nubra Valley region has been used to estimate the earthquake source parameters. The source parameters viz., seismic moment, source radius and stress drop of these events have been estimated following Brune’s earthquake source model (1970). The low frequency spectral level and corner frequency has been estimated from the displacement spectra and has been used to estimate the source parameters. The seismic moment ranges between 2.1 x 1020 to 3.34 x 1023 dyne-cm for seismic events with magnitudes ranges between 2.7 to 5.0. The circular source radius (r) calculated using Brune’s formula lies in the range 693.2 m to 1.296 km. The estimated stress drops ranges between 0.1 to 61.7 bars and found in agreement with the other region of Himalaya. The stress drop shows increasing trend with seismic moment for magnitudes less than 3.8 and becomes constant for higher magnitude events, this observation has been reported in various studies,
The present study aims to estimate the frequency-dependent attenuation relations and source parameters of local earthquakes that occurred in the Garhwal Lesser and the Higher Himalaya around Uttarkashi town, India. The local earthquake data of 234 events recorded from a 12-station digital telemetered local seismological network in the region during 2008 to 2017 have been used for this purpose. The first data set of 126 events occurred around Uttarkashi in the Lesser Himalaya, the second data set of 73 events located northwest of Uttarkashi in the Higher Himalaya and the third data set of 35 events located about 35 km east of Uttarkashi in the vicinity of 1991 Uttarkashi earthquake (Ms ~ 6.8) in the Higher Himalaya. The source parameters such as: seismic moment (Mo), source radius (r) and stress drop (∆σ), have been estimated from the displacement spectrum of the SH component of S-wave by applying Brune’s circular source model (Brune in J Geophys Res 75: 4997 5009, 1970). The attenuation characteristics are examined by estimating the quality factor (Qc) from the decay of coda waves of vertical component record using the Single Backscattering model (Aki and Chouet in J Geophys Res 80: 23 3322 3342, 1975). The Qc estimated at different values of frequency (1.5 to 24 Hz) have shown that Qc a function of frequency. Here, we obtain the following frequency-dependent attenuation relationships: Qc = 110 \({f}^{0.99}\) (using first and second data sets) and Qc = 142 \({f}^{0.87}\) (using third data set). The source parameters of 234 events show that more than 96% of events (227 events) have a low stress drop (less than 10 bars), five events have a stress drop between 10 and 100 bars and two events have exceptionally high stress drop of 271 and 532 bars. This shows that the region produces, by and large, low stress drop events. The variation in stress drops with depth demonstrates no clear increase or decrease in stress drop with focal depth. The Mo-fc scaling relations have been obtained for events with magnitudes two and above, Mo = 2.7 × 1016 fc−3.98 (for data set 1), Mo = 1.4 × 1014 fc−2.74 (for data set 2), and Mo = 1.1 × 1015 fc−3.28 (for data set 3).
The Indo-Burma Ranges (IBRs) and its surrounding North-east India is one of the seismotectonically active subduction systems in the world, where the Indian Plate is subducting beneath the Sunda Plate. This has resulted in major earthquakes in the past. In this study, spectral analysis of S-wave has been used to investigate the source parameters for local earthquakes (3.3 ≤ MD ≤ 5.8) exclusively in the
Indo-Burma region fusing a network of six stations by adopting the Brune model. The corner frequencies (fc) of the events are varied from 0.6 to 3.2 Hz. The estimated source parameters lie in the range from 9 � 1013–3.7 � 1017 N m, 0.2–35.1 MPa, 410–1,956.4 m, 0.002–1.196 m, and 2.9–13.5 Hz for seismic moment M0, stress
drop (Δσ), source radius, source dislocation, and maximum cut-off frequency (fmax), respectively. The scaling relation between M0 and fc has been derived as M0 = 1.622 � 1016 fc 5.298. The scaling relations of M0 with fmax and stress drop have also been derived. The high-stress drops (>10 MPa) were at a depth zone of ~40–60 km, while the stress drops were less than 4.0 MPa beyond this depth, indicating the shallow and deeper portion of the lithosphere to be relatively brittle. We postulate that this could occur due to a complex detachment process as a result of slab tearing in the region. The upper boundary of stress drop was found to have an increasing trend with the focal depth of the earthquakes. The empirical relations
between M0 MD and MW MD have also been derived for the IBRs. The estimated source parameters and scaling relations will be useful in estimations of lithospheric strength, simulation of strong ground motion in the IBRs, and calibrating the coefficient of the local earthquakes in the IBR and its surrounding region.
This study reports the estimation of source parameters in and around Izmir, western Anatolia (Turkey), using data recorded by 18 strong motion stations belonging to the local accelerometer array (IzmirNET). The displacement spectra of SH waves are calculated for 55 earthquakes with a moment magnitude range (Mw) of 3.4 to 5.7 recorded by at least ten stations. The corner frequency (f0), spectral level and fmax are acquired from the displacement spectra in order to analyse the source characteristics of the events using Brune’s source model. Seismic moment (M0) values are computed between 12.74 and 17.93 Nm, spectral level (Ω0) values are detected between 3.17 and 6.44 nm s, source radius (r) values are calculated from 0.45 to 2.28 km, and seismic energy values are estimated between 2.07 × 1013 and 6.45 × 1020 erg. Computed stress drop (Δσ) values vary from 0.72 to 346.9 bar, and this result is significantly lower than the values of 0.017 and 647.6 bar reported for the Marmara region, northwestern Anatolia (Turkey), and slightly lower than the source sizes of the events of between 0.0862 and 5.1042 km. However, similar results were found for seismic moments (Koseoglu et al., in J Seismol 18:651–669, https://doi.org/10.1007/s10950-014-9435-2, 2014). From the results of the present study, it is concluded that scattering in seismic moment, stress drop and hypocentral distance during large earthquakes is observed by an increase in f0 and fmax , which is related to the complex tectonism of the study area.
In the literature, assuming independence of random variables X and Y, statistical estimation of the stress-strength parameter R = P(X > Y) is intensively investigated. However, in some real applications, the strength variable X could be highly dependent on the stress Y. In this paper, unlike the common practice in the literature, we discuss on estimation of the parameter R where more realistically, X and Y are dependent random variables distributed as bivariate Rayleigh model. We derive the Bayes estimates and highest posterior density credible intervals of the parameters using suitable priors on the parameters. Because there are not closed forms for the Bayes estimates, we will use an approximation based on Laplace method, and a Markov Chain Monte Carlo technique to obtain the Bayes estimate of R and unknown parameters. Finally, simulation studies are conducted in order to evaluate the performances of the proposed estimators and analysis of two data sets are provided.
Source parameters of 41 local events
(0.5 B ML B 2.9) occurred around Bilaspur region of the Himachal
Lesser Himalaya from May 2013 to March 2014 have been
estimated adopting Brune model. The estimated source parameters
include seismic moments (Mo), source radii (r), and stress drops
(Dr), and found to vary from 4.9 9 1019 to 7 9 1021 dyne-cm,
about 187–518 m and less than 1 bar to 51 bars, respectively. The
decay of high frequency acceleration spectra at frequencies above
fmax has been modelled using two functions: a high-cut filter and j
factor. Stress drops of 11 events, with M0 between 1 9 1021 and
7 9 1021 dyne-cm, vary from 11 bars to 51 bars with an average of
22 bars. From the variation of the maximum stress drop with focal
depth it appears that the strength of the upper crust decreases below
20 km. A scaling law M0 = 2 9 1022 fc
-3.03 between M0, and
corner frequency (fc), has been developed for the region. This law
almost agrees with that for the Kameng region of the Arunachal
Lesser Himalaya. fc is found to be source dependent whereas fmax is
source independent and seems to indicate that the size of the
cohesive zone is not sensitive to the earthquake size. At four sites
fmax is found to vary from 14 to 23, 11 to 19, 9 to 23 and 4 to
11 Hz, respectively. The j is found to vary from 0.01 to 0.035 s
with an average of 0.02 s. This range of variation is a large compared
to the j variation between 0.023 and 0.07 s for the Garhwal
and Kumaon Himalaya. For various regions of the world, the j
varies over a broad range from 0.003 to 0.08 s, and for the Bilaspur
region the j estimates are found to be consistent with other regions
of the world.
The Department of Earthquake Engineering, Indian Institute of Technology Roorkee has been
monitoring the local seismicity in Tehri region employing a radio-linked local seismological
network on behalf of the Tehri Hydro Development Corporation (THDC), India Ltd. from the
last more than fourteen years. This network has been deployed for the purpose of collecting data
of local earthquakes around Tehri region to study the attributes of the local seismicity in the
environs of 260.5 m high Tehri dam. The network, commissioned in the region in September
1993, comprised of six remote seismological stations telemetered to the central recording station
(CRS) located at New Tehri Town (NTT). In November-December, 2007, this network has been
expanded and upgraded from six remote stations to twelve remote stations. All the equipment of
the earlier VHF telemetry network has been replaced by the new equipment comprises of stateof-
the-art 24-bits digital telemetry. The present paper presents the details of equipment deployed
along with the discussions about the salient features of the results obtained in this study.
The characteristics of earthquake source can be well explained by the estimation of source parameters of that area. A moderate earthquake of magnitude 4.7 occurred on November 6, 1975 around Roorkee region of India. An attempt has been made to understand the seismic pattern and behavior of the earthquakes around Roorkee and its adjacent areas. The source parameters of 65 events have been estimated using the spectral analysis of SH-component of shear waves from the three component digital seismogram applying Brune model which falls in the study area encompassing Garhwal Lesser Himalaya and Indo-Gangetic plains. The values of Seismic moment (M0), Moment magnitude (Mw), Source radii (r) and Stress drops (σ) of sixty five events vary from 1.58 x 1011 (Nm) to 1.99 x 1014 (Nm), 1.4 to 3.3, from 139 m to 397.4 meters and between 0.199 bars to 25.8 bars. The values of stress drop increase significantly towards Indo-Gangetic plain indicating stress buildup. Two different data have been taken for computation of M0 vs. f0 scaling law, as generally breakdowns of self similarity have reported for events with moment magnitude less than 2.5. Another empirical relation Log M0 (N m) = 2.610 ML + 10.301 has been estimated between the seismic moment, M0 and local magnitude ML. This relation can be adopted to estimate Mw from ML in the magnitude range from 0.5 to 4.5. The near surface attenuation factor (κ) is found to be large, of the order of 0.02 suggesting thick low velocity sediment beneath the region.
