Attenuation of coda waves in the Garhwal Himalaya, India

Gupta, Subhash; Singh, Vipul; Kumar, Ashwani

doi:10.1016/0031-9201(94)02968-h

Cited by 104 publications

(51 citation statements)

References 9 publications

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“…It would be worthwhile to mention that the earlier estimation of coda Q c for the region suggested quite a high value of Q o (126) which can be explained in terms of a constant 2.56 s RMS window for all the central frequencies (F m ) (where a time window of the order of 5=f Ã SPS Vol. 158, 2001 Aftershock Activity and Low Coda Q c should be used) and only seven earthquakes considered for the study (GUPTA et al, 1995b). In addition the study of KUMAR et al (1999), based on earlier Q c relation Q 126f 0:95 , revealed inconsistencies between observed and synthetic peak values for the ground acceleration which can be attributed to the Q c relation considered by them.…”

Section: Decay Of Acceleration With Distancementioning

confidence: 95%

“…The utilities of these kinds of studies are quite signi®cant in estimating the seismic hazard of a region. The decay of amplitude with distance for dierent Q o values (i.e., 30 from this study and 126 from GUPTA et al, 1995b) is estimated (Fig. 9).…”

Section: Decay Of Acceleration With Distancementioning

confidence: 99%

“…GUPTA et al (1995b) suggested a frequency-dependent coda-Q c relation for the Garhwal Himalaya i.e., Q c 126f 0.95 indicating less pronounced attenuation at higher frequencies. The dierent Q o estimations can be attributed to the dierent techniques used by them.…”

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confidence: 99%

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Aftershock Activity and Frequency-dependent Low Coda Qc in the Epicentral Region of the 1999 Chamoli Earthquake of Mw 6.4

Mandal¹,

Padhy²,

Rastogi³

et al. 2001

Pure appl. geophys.

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Ð On 28 March, 1999 (19:05:10.09, UT) a signi®cant earthquake of M w 6.4 occurred in the Garhwal Himalaya (30.555°N, 79.424°E). One hundred and ten well-recorded aftershocks show a WNW-ESE trending northeasterly dipping seismic zone extending from a depth of 2 to 20 km. As the main shock hypocenter occurred at the northern end of this seismic zone and aftershocks extended updip, it is inferred that the main-shock rupture nucleated on the detachment plane at a depth of 15 km and then propagated updip along a NE-dipping thrust plane. Further, the epicentral distribution of aftershocks de®nes a marked concentration near a zone where main central thrust (MCT) takes a signi®cant turn towards the north, which might be acting as an asperity in response to the NNE compression due to the underthrusting of Himalayan orogenic process prevalent in the entire region. Presence of high seismicity including ®ve earthquakes of magnitude exceeding 6 and twelve earthquakes of magnitude exceeding 5 in the 20th century is presumed to have caused a higher level of shallow crustal heterogeneity in the Garhwal Himalaya, a site lying in the central gap zone of the Himalayan frontal arc. Attenuation property of the medium around the epicentral area of the 1999 Chamoli earthquake, covering a circular area of 61,500 km 2 with a radius of 140 km, is studied by estimating the coda Q c from 48 local earthquakes of magnitudes varying from 2.5±4.8. These earthquakes were recorded at nine 24-bit REFTEK digital stations; two of which were equipped with three-component CMG40T broadband seismometers and others with three-component L4-3D short-period seismometers. The estimated Q o values at dierent stations suggest on average a low value of the order of (30 0.8), indicating an attenuating crust beneath the entire region. The frequency-dependent relation indicates a relatively low Q c at lower frequencies (1±3 Hz) that can be attributed to the loss of energy due to scattering on heterogeneities and/or the presence of faults and cracks. The large Q c at higher frequencies may be related to the propagation of backscattered body waves through deeper parts of the lithosphere where less heterogeneities are expected. An important observation is that the region north of MCT (more rigid highly metamorphosed crystalline rocks) is less attenuative in comparison to the region south of MCT (less rigid slightly metamorphosed rocks (sedimentary wedge)). The acceleration decays to 50% at 20 km distance and to 7% at 100 km. Hence, even 1g acceleration at the source may not cause signi®cant damage beyond 100 km in this region.

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Section: Decay Of Acceleration With Distancementioning

confidence: 95%

Section: Decay Of Acceleration With Distancementioning

confidence: 99%

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Aftershock Activity and Frequency-dependent Low Coda Qc in the Epicentral Region of the 1999 Chamoli Earthquake of Mw 6.4

Mandal¹,

Padhy²,

Rastogi³

et al. 2001

Pure appl. geophys.

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“…5 and Table 3. It is found that the best-fitted line obtained here generally lies above that of Garhwal Himalaya (Gupta et al 1995), North East India (Gupta and Kumar 2002), Andaman (Parvez et al 2008), Koyna (Mandal and Rastogi 1998), and Kumaun Himalaya (Paul et al 2003). On the other hand, the attenuation value is comparatively less than that of Indian Shield (Singh et al 1999), Jabalpur Region (Singh et al 2004), and Central India (Mandal et al 2013) at low frequencies and gradually increases and exceeds at higher frequency.…”

Section: Resultsmentioning

confidence: 45%

Coda Q in Eastern Indian shield

2015

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. Thus, the attenuation follows the power law relationships (e.g., Q c = Q 0 f n ), and the moderate to higher values of frequency parameters (n) obviously show that the Q c value is a strong function of frequency. The increasing values of Q 0 with increasing lapse time indicating the depth dependency of attenuation, and accounts for decreasing heterogeneity towards deeper level beneath the study area.

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“…In India, attenuation characteristics of a few regions have been investigated using coda waves: These include, Central and Western Himalayas (GUPTA et al, 1995;NARESH et al, 2005 andMUKHOPADHYAY et al, 2006), Koyna region (GUPTA et al, 1998), Kachchh (GUPTA et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

Coda Q Estimates in the Andaman Islands Using Local Earthquakes

Parvez

Sutar

Mridula

et al. 2008

Pure appl. geophys.

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Abstract-The attenuation property of Andaman Island has been investigated analyzing coda waves from 57 local earthquakes in the magnitude range of 2.0-4.9, using the single backscattering model. These earthquakes waveforms, recorded on five broadband seismographs sited over the island from north to south during Nov. , corresponding to lapse time window lengths of 40 and 80 s, respectively. The variation of Q c with frequency, lapse time and also with the location of seismograph reflects the marked structural and compositional inhomogeneity with depth along the Andaman Islands. These observations are well correlated with the seismicity pattern and distinct high angle subduction beneath the island.

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Attenuation of coda waves in the Garhwal Himalaya, India

Cited by 104 publications

References 9 publications

Aftershock Activity and Frequency-dependent Low Coda Qc in the Epicentral Region of the 1999 Chamoli Earthquake of Mw 6.4

Aftershock Activity and Frequency-dependent Low Coda Qc in the Epicentral Region of the 1999 Chamoli Earthquake of Mw 6.4

Coda Q in Eastern Indian shield

Coda Q Estimates in the Andaman Islands Using Local Earthquakes

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