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Estimation of Seismic Kappa Parameter and Near-Surface Attenuation in Morocco

Boulanouar Abderrahim, Mittal Himanshu, Rahmouni Abdelaali, Zian Ahmed, Chourak Mimoun, Géraud Yves, Harnafi Mimoun, Sebbani Jamal

Ecological Engineering & Environmental Technology

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2022

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Vol. 23, iss. 6

128--139

EN

The goal of this study is to estimate the kappa (κ) parameter for a group of 12 broadband stations, located in different geological structures in Morocco, a country with moderate seismic activity. In this study, the kappa, κ has been obtained from the spectral analysis of the shear waves of 42 earthquakes, recorded in Morocco. Using 321 seismograms recorded in the period between 2009 and 2012 by the Picasso Project, the average κ-values have been computed from the horizontal components. For each station, the relationship between κ values and the hypocentral distance was determined. We separately investigated and studied the distance dependence of the stations located on soft soil and hard rock sites. The estimated average factor of the κ value ranges from 0.0682 for the hard sites to 0.0763 for the soft sites, with 0.072 as an average value. The lack of a significant correlation found between κ and magnitude at all stations considered in this study suggests that kappa is mainly dependent on local site characteristics. To the best of our knowledge, no studies related to kappa parameter estimation have been published for this region. The results generated in this study can be used for the seismic hazard evaluation of Morocco.

2

Spatial distribution of high frequency spectral decay factor kappa (κ) for Delhi, India

Mittal Himanshu, Sharma Babita, Sandhu Manisha, Kumar Dinesh

Acta Geophysica

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2021

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Vol. 69, no. 6

2113--2127

EN

The recorded strong motion data in the Delhi region provide an excellent opportunity to study high-frequency decay parameter, kappa (κ) for the National Capital (Delhi) region and to further understand its implications to study the site effects characterized by different stations within the vicinity of the study region. The kappa values are estimated at 30 locations from 99 accelerograms of 19 earthquakes recorded in the Delhi region and are found to vary from place to place depending upon the controlling parameters, primarily the site characterization. The estimated average values of ‘κ’ lie in the range 0.0118–0.0537 s for the various locations of the region depending upon the source, path, and site characteristics of earthquakes considered in the present study. The distance dependence is found insignificant, while there is a scatter in the variation of κ values with that of magnitude which indicates that κ is more related to the site characteristic for the entire Delhi region which in turn reveals the fact of the basic criterion of the κ parameter. To affirm the total attenuation on the instruments, the site effects demonstrate the behavior of amplification to the geological exposure. It has been found that the various sites under consideration for the study area amplify between 0.6 and 7.0 Hz predominant frequency ( fpeak) and agree with the geological arrangements of the region. Based on the present study, the most vulnerable areas are the northeastern region of Delhi which lies in proximity to the food plains of Yamuna river and alluvial deposits of younger origins of the foreland basin along with the southwestern part of Delhi capital which is comprised of the water-saturated alluvial deposits. The estimated ‘κ’ values are found to be correlated with those of the estimated site amplification and are useful in strong ground motions simulation for the proper evaluation of seismic hazard to build a seismic risk resilient society.

3

Time dependent shake map for Uttarakhand Himalayas, India, using recorded earthquakes

Mittal Himanshu, Wu Yih-Min, Lin Ting-Li, Legendre Cédric P., Gupta Sushil, Yang Benjamin M.

Acta Geophysica

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2019

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Vol. 67, no. 3

753--763

EN

Uttarakhand Himalayas are highly sensitive to seismic hazard with possible occurrence of high-magnitude earthquakes. Fewer waveforms are available from previously recorded earthquakes, which are insufficient for carrying out seismic hazard studies. The recently installed strong motion instrumentation network (SMIN) in India, particularly, in Indian Himalayas is providing useful data. Using recorded data from SMIN, time-dependent peak ground acceleration and observed peak ground velocity shake maps are drawn for two earthquakes widely recorded by SMIN in Uttarakhand region of Indian Himalayan belt. Open-source Earthworm software with new algorithms is used for drawing these shake maps. The source mechanism is computed for April 4, 2011 earthquake using waveform inversion technique to relate it to the trend of shake maps. The computed focal mechanism shows one of the nodal planes in NW–SE, which are consistent with shake maps for the same earthquake. These time-dependent plotted shake maps provide useful information on the initial rupture, as well as the potential directivity of the rupture.

4

Testing the performance of earthquake early warning system in northern India

Mittal Himanshu, Wu Yih‑Min, Sharma Mukat Lal, Ming Yang Benjamin, Gupta Sushil

Acta Geophysica

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2019

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Vol. 67, no. 1

59--75

EN

The main goal of present study is to test the functionality of an earthquake early warning (EEW) system (a life-saving tool), in India using synthesized data and recorded earthquake data from Taiwan. In recent time, India set up an EEW system in the central seismic gap along the Himalayan Belt, consisting of about 100 low-cost P-Alert instruments. The area, where these instruments are installed, is highly sensitive to the seismic risk with the potential of strong, major and great earthquakes. In the absence of recorded data from the Himalayas required for analysis of such system, we take advantage of recorded waveforms from Taiwan, to test the EEW system. We selected Taiwanese stations in good accordance with the Indian sensor network, to have a best fit in terms of inter station spacing. Finally, the recorded waveforms are passed through Earthworm software using tankplayer module. The system performs very well in terms of earthquake detection, P-wave picking, earthquake magnitude and location (using previously estimated regressions). Pd algorithm has been tested where the peak amplitude of vertical displacement is used for estimating magnitudes using previously regressed empirical relationship data. For the earthquakes located between Main Boundary Thrust and Main Central Thrust along with a matching instrumentation window, a good estimate of location, as well as magnitude is observed. The approach based on Pd for estimating magnitude works perfectly as compared to _ c approach, which is more sensitive to signal-to-noise ratio. To make it more region specific, we generated synthetic seismograms from the epicenters of historical Chamoli (1999) and Uttarkashi (1991) earthquakes at EEW stations in India and checked the functionality of EEW. While placing these earthquakes within the instrumentation window, a good approximation of earthquake location and magnitude is obtained by passing these generated waveforms. The parameters used to judge the performance of EEW system included the time taken by the system in issuing warning after the confirmation of the occurrence of damaging earthquake and the lead time (time interval between the issuing of warning and arrival of damaging earthquake ground motion at a particular location). High lead times have been obtained for the plainer regions including thickly populated regions of Gangetic plains, such as Delhi National Capital Region according to the distance from the epicenter, which are the main target of EEW system.