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ATTENUATION OF Lg WAVES IN THE CANADIAN SHIELD.
Abstract
An empirical model that relates Fourier amplitude density of ground acceleration (FA) of Lg waves of Canadian Shield earthquakes to magnitude and distance has been calibrated at discrete frequencies. Magnitude (m//b//L//g) ranges from 2. 8 to 5. 2, epicentral distance (R) from 70 to 900 km, and frequency (f) from 0. 6 to 20 Hz. The data base consists of the vertical component of Lg waves as recorded in digital format by the Eastern Canada Telemetered Network. A linear regression is applied to the logarithm of the following model: FA equals ke**b**m**b**L**ge** minus ** gamma **RR** minus **0**. **5, where k equals (2 pi f)**2c and c is a constant coefficient (related to the prototype Fourier amplitude density of ground displacement), b reflects the magnitude dependence, gamma is the anelastic attenuation coefficient, and 0. 5 is the geometric spreading factor of surface waves. The magnitude coefficient, b, varies from a maximum of 3. 0 at 1 Hz to 1. 8 at 20 Hz, a trend indicative of the decrease in corner frequency with increasing magnitude.
... Some other Coda-Q studies are for Central India by Mandal et al. (2013), N-W Himalayas by Kumar et al. (2005) and Indian Shield by Singh et al. (2004). A number of similar Q c studies have also been carried out for numerous regions around the world such as for Canada by Hasegawa (1985), for Eastern USA by Gupta and McLaughin (1987), for Dead Sea region by Van Eck (1988) and many more. This study aims to develop a κ model and carry out Coda-Q estimation at different lapse time windows for the ECNP region. ...
... Based on the above statement, it has been found from previous studies that active regions tend to have Q o < 200 and n > 0.9 which can be inferred from (Rovelli 1982). While the stable regions generally have Q o > 600 and n < 0.4 which include regions such as Indian Shield (Singh et al. 2004), Canadian Shield (Hasegawa 1985), Eastern Canada (Chun et al. 1987) and Eastern US (Gupta and McLaughin 1987). For moderate regions, Q o value lies between 200 and 600 (Kumar et al. 2005). ...
The Chotanagpur Plateau (CNP) forms an important part of the Indian Shield, has experienced moderate seismicity in the past. There are records of significant historical earthquakes that occurred in 1868 Hazaribagh (maximum observed intensity VI), 1811 Kolkata (M 5.0), 1963 Singhbhum (M 5.2) and 1969 Bankura (M 5.7). Hence, in order to carry out seismic hazard studies, it is important to study the seismicity of this region. Kappa (κ) and Coda-Q are important attenuation parameters that can aid in the stochastic simulation of ground motion and development of region-specific Ground Motion Prediction Equations (GMPEs). In this study, κ model is developed using the classical method by Anderson and Hough (Bull Seism Soc Am 74:1969–1993, 1984) and Coda-Q is estimated using Single backscattering model by Aki and Chouet (J Geophys Res 80:3322–3342, 1975). Seismic data used include 139 accelerograms obtained from six broadband stations, i.e., IIT(ISM), Sahibganj (SBG), Khunti (KNTI), Nirsa (NRS), Bokaro (BOK) and Peterwar (PTWR). The average value of κ is found to be 0.0364 which is found to be dependent on epicentral distance. The Qc values are calculated for three Coda windows, i.e., 40, 50 and 60 s and are found to be strongly dependent on frequency as they increase with it. Extinction distance results show that the upper mantle is relatively homogeneous and the attenuation below 86–119 km depth is less. The Qc and ‘n’ values on comparison with the regional as well as the global studies are found to lie in intermediate range indicating moderate seismicity and presence of heat zones in the Eastern Chotanagpur Plateau (ECNP) region.
... S waves within the crust exhibit a near total reflection at the surface and the crust-mantle boundary. The Lg wave propagates efficiently over continental paths and has been observed at distances up to 30° in the Canadian Shield (Hasegawa 1985). However, Lg does not propagate efficiently in very thin crust (< 10 km) due to its inability to maintain the crustal reverberations needed to generate Lg (e.g. ...
... China and can be modelled as the sum of higher mode surface waves Knopoff et al. 1973;Herrmann & Kijko 1983) or as many supercritically reflected crustal S waves (e.g. . This wave only propagates efficiently over continental paths and can be seen at distances up to 30 • in the Canadian Shield (Hasegawa 1985). The study of Lg wave attenuation has often been used for characterizing crustal structure since the sensitivity of the Lg wave to crustal properties makes it an important tool in better understanding the underlying causes of seismic anomalies in the crust Ni & Barazangi 1983;McNamara et al. 1996;. ...
The Northeast (NE) China is a geologically complex as well as a geopolitically sensitive region. The region is currently undergoing an extension and it is also experiencing an active intraplate continental magmatism. Prior to the deployment of the NorthEast China Extended Seismic (NECESS) Array only a few studies on regional seismic attenuation have been conducted in the region. Regional seismic wave attenuation is an important indirect indicator of lithospheric temperature and rheology. Regional wave attenuation wave models are extensively utilized to discriminate between the nuclear explosions and earthquakes and also to calculate the yields in nuclear explosions.
In this study, regional seismic wave forms recorded primarily by NECESSArray is used to study Pg and Lg attenuation in NE China, implementing Two Station Method (TSM) and Reverse Two Station Method (RTSM). In both the TSM and RTSM, the source and site terms are assumed to be effectively divided out and thus do not need to be known a priori.
Lg attenuation at 1 Hz was initially studied implementing reverse two station/two event method and only using data derived from 78 crustal earthquakes that were recorded by NECESSArray from 2011 to 2013. The 2-D tomographic image obtained shows a high degree of lateral variation in Lg attenuation throughout NE China. High Q 0 values were observed in the Great Xing’an Rage, Lesser Xing’an Range and Songen-Zhangguangcai Ranges. Low Q 0 values were observed in Songliao, Sanjiang and Erlian Basins and the lowest Q 0 values were observed in Holocene volcanic fields such as Wudalianchi. Most of the low Q 0 values in NE China correlates well with the low crustal Rayleigh wave phase velocity anomalies, sediments and Holocene volcanism.
Geometric spreading coefficients calculated in the frequency domain for both Pg and Lg using TSM raypaths were found to be different from the values used in previous studies. Geometric spreading coefficients of 0.9 and 0.35 were obtained for Pg and Lg, respectively. Pg attenuation map produced using 2909 two station raypaths at a central frequency of 1 Hz shows an average Q 0 value of 299 in NE China. The map shows low Q 0 (< 400) values in the northern and southern Great Xing’an Range, Lesser Xing’an Range, and eastern part of the Songliao Basin. The central part of the Great Xing’an Range and central part of the Songliao Basin show medium to high Q 0 (> 400) values. The low Pg Q 0 values observed could be attributed to continuous leakage of Pg energy in the mountainous regions and the high Q 0 values observed over the basin could be due to the shallow low velocity zone or due to the seismic amplification.
Lg attenuation images with 2°× 2° resolution were produced implementing both TSM and RTSM at several narrow bandwidths with central frequencies of 0.5, 1, 2 and 3 Hz. Lg attenuation images produced at low frequencies (≤ 1 Hz) utilizing both TSM and RTSM, show low Q values in basins and high Q values in the mountain ranges. However, at higher frequencies (≥ 2 Hz) both basins and mountain ranges show high Q values. RTSM consistently show higher Q values than the TSM while both methods show similar frequency dependent factors (η). We obtained η values of 0.49 and 0.46
for TSM and RTSM, respectively.
The site responses for both Pg and Lg were calculated using RTSM. Pg site responses calculated at 1 Hz show amplification in Erlian, Hailar and Songliao Basins and deamplification in Sanjiang Basin, Lesser Xing’an Range and Songen- Zhangguangcai Ranges. Lg site responses calculated at central frequencies of 0.5, 1, 2 and 3 Hz show high degree of lateral variation as well as frequency dependence. At low frequencies (≤ 1 Hz) almost all the seismic stations in the sedimentary basins show amplification and at higher frequencies (≥ 2 Hz) seismic stations in Lesser Xing’an Range and Songen-Zhangguangcai Ranges show deamplification. Maximum site amplification frequency (resonant frequency) of all the stations in the Songliao Basin was plotted against the interpolated sediment thickness underneath each station in the Songliao Basin. Parolai et al., (2002) observed a power law relationship between the sediment thickness and the resonant frequency in a sedimentary basin in Cologne, Germany. However, we did not observe similar relationship between the resonant frequency and the sediment thickness in NE China.
... As expected, the Q C (f) obtained for the Baikal rift is similar to the ones found in areas with high tectonic activity. At the same time, the frequency parameter obtained for the Siberian Platform (n = 0.48) matches n values found for stable or weakly deforming areas (Fig. 11a) such as North Iberia (n = 0.45) (Pujades et al., 1991), the Canadian Shield (n = 0.35) (Hasegawa, 1985) and New England (n = 0.40) (Pulli, 1984). ...
... Similar behavior of δ and n with depth was noted in the south Kenya rift and the Basin and Range Province (Dobrynina, 2013;Dobrynina et al., 2012). Thus, the change in attenuation parameters with depth is clearly related to the velocity (Dutta et al., 2004), New England (Q C (f) = 460f 0.4 ) (Pulli, 1984), North Iberia (Q C (f) = 600f 0.45 ) (Pujades et al., 1991), Canadian Shield (Q C (f) = 900f 0.35 ) (Hasegawa, 1985), North American Platform (Central USA)(Q C (f) = 1000f 0.2 ) (Singh and Herrmann, 1983), Siberian Platform (Q C (f) = 134f 0.48 ) (the present work); (b) zones with active tectonics: North Eastern India (Q C (f) = 52f 1.32 ) (Hazarika et al., 2009), Delhi, India (Q C (f) = 142f 1.04 ) (Mohanty et al., 2009), Himalaus (Q C (f) = 110f 1.02 ) (Gupta and Kumar, 2002), Central Iran (Q C (f) = 101f 0.94 ) (Ma'hood and Hamzehloo, 2009), Japan (Q C (f) = 47f 1.06 ) (Matsumoto and Hasegawa, 1989), Parkfield, California (Q C (f) = 79f 0.74 ) (Hellweg et al., 1995), the Baikal rift system (Q C (f) = 124f 0.92 ) (present work) for the same lapse time windows W = 30 s for all regions according to Gusev (1995). 83 60 174 135 150 15 134 77 92 65 178 140 155 20 138 84 99 70 183 146 161 25 143 91 106 75 187 152 167 30 147 98 113 80 192 157 172 35 152 105 120 85 196 162 177 40 156 111 126 90 201 168 183 45 161 117 132 95 205 173 188 50 165 123 138 100 209 178 193 55 170 129 144 Comment: 1lapse time window (in sec), 2the largest axis, 3the smallest axis, and 4the depth of ellipsoid's lower border. ...
... As expected, the Q C (f) obtained for the Baikal rift is similar to the ones found in areas with high tectonic activity. At the same time, the frequency parameter obtained for the Siberian Platform (n = 0.48) matches n values found for stable or weakly deforming areas (Fig. 11a) such as North Iberia (n = 0.45) (Pujades et al., 1991), the Canadian Shield (n = 0.35) (Hasegawa, 1985) and New England (n = 0.40) (Pulli, 1984). ...
... Similar behavior of δ and n with depth was noted in the south Kenya rift and the Basin and Range Province (Dobrynina, 2013;Dobrynina et al., 2012). Thus, the change in attenuation parameters with depth is clearly related to the velocity (Dutta et al., 2004), New England (Q C (f) = 460f 0.4 ) (Pulli, 1984), North Iberia (Q C (f) = 600f 0.45 ) (Pujades et al., 1991), Canadian Shield (Q C (f) = 900f 0.35 ) (Hasegawa, 1985), North American Platform (Central USA)(Q C (f) = 1000f 0.2 ) (Singh and Herrmann, 1983), Siberian Platform (Q C (f) = 134f 0.48 ) (the present work); (b) zones with active tectonics: North Eastern India (Q C (f) = 52f 1.32 ) (Hazarika et al., 2009), Delhi, India (Q C (f) = 142f 1.04 ) (Mohanty et al., 2009), Himalaus (Q C (f) = 110f 1.02 ) (Gupta and Kumar, 2002), Central Iran (Q C (f) = 101f 0.94 ) (Ma'hood and Hamzehloo, 2009), Japan (Q C (f) = 47f 1.06 ) (Matsumoto and Hasegawa, 1989), Parkfield, California (Q C (f) = 79f 0.74 ) (Hellweg et al., 1995), the Baikal rift system (Q C (f) = 124f 0.92 ) (present work) for the same lapse time windows W = 30 s for all regions according to Gusev (1995). 83 60 174 135 150 15 134 77 92 65 178 140 155 20 138 84 99 70 183 146 161 25 143 91 106 75 187 152 167 30 147 98 113 80 192 157 172 35 152 105 120 85 196 162 177 40 156 111 126 90 201 168 183 45 161 117 132 95 205 173 188 50 165 123 138 100 209 178 193 55 170 129 144 Comment: 1lapse time window (in sec), 2the largest axis, 3the smallest axis, and 4the depth of ellipsoid's lower border. ...
... It has been shown (Wu and Aki, 1988) that a simultaneous calculation of the values of Q i and Q s from coda waves can lead to unacceptably large errors in both quantities, and, therefore, the single backscattering model is most appropriate for calculating the Q factor from coda waves. The attenuation of seismic waves has been the subject of numerous theoretical and experimental studies of domestic and foreign authors (Aki, 1969;Aki and Chouet, 1975;Aptikaeva, 1991;Emanov et al., 1999;Gao et al., 1983;Gupta and Kumar, 2002;Gusev and Lemzikov, 1985;Hasegawa, 1985;Havskov and Ottemoller, 2003;Hazarika et al., 2009;Johnston et al., 1981;Kopnichev, 1991;Kopnichev and Sokolova, 2003;Mak et al., 2004;Mitchell, 1981;Pulli, 1984;Rautian and Khalturin, 1978;Sato, 1977;Zhadin and Dergachev, 1973;and others). ...
... For example, the unactive Siberian Platform, whose basement is dated to the Archean-lower Proterozoic, is characterized by attenuation parameters δ = 0.007 km -1 and n = 0.48. According to (Mak et al., 2004), this value of the frequency parameter is characteristic of regions with moderate and stable tectonics, such as Northern Iberia (n = 0.45) (Pujades et al., 1991), the Canadian Shield (n = 0.35) (Hasegawa, 1985), and New England (n = 0.40) (Pulli, 1984). At the same time, the younger (Vendian) East Sayan block is characterized by high attenuation parameters: δ = 0.009 km -1 and n = 0.89. ...
... It may be stated from the entire discussion that the study region accounts for moderate to higher attenuation of seismic shear wave. During worldwide comparison (Fig. 5), lesser attenuation relative to Eastern Canada (Chun et al. 1987;Shin and Herrmann 1987), Canadian Shield (Hasegawa 1985), Eastern United States (Gupta and McLaughin 1987), Central Appalachia (Shi et al. 1996), Gupta and Kumar (2002) 2. Sourashtra 170f 0.97 Sharma et al. (2012) 3. Kachchh 148f 1.01 Sharma et al. (2008) 4. Andaman 119f 0.8 Parvez et al. (2008) 5. Koyna 169f 0.77 Mandal and Rastogi (1998) 6. Garhwal Himalaya 110f 1.02 Gupta et al. (1995) 7. Indian Shield 508f 0.48 Singh et al. (1999) 8. Kumaun Himalaya 92f 1.07 Paul et al. (2003) 9. ...
... Jabalpur Region 339f 0.63 Singh et al. (2004) 11. NW Himalaya 158f 1.05 Kumar et al. (2005) 12. Central India 332f 0.59 Mandal et al. (2013) Shin and Herrmann (1987) 2. Canadian Shield 900f 0.2 Hasegawa (1985) 3. Eastern Canada 1100f 0.19 Chun et al. (1987) 4. Eastern United States 800f 0.32 Gupta and McLaughin (1987) 5. Central Appalachia 570f 0.46 Shi et al. (1996) 6. Adirondack Mountains 905f 0.4 Shi et al. (1996) 7. New England 460f 0.4 Pulli (1984) 8. Baltic Shield 125f 1.08 Kvamme and Havskov (1989) 9. Southern Italy 62.5f 0.7 Tuve et al. (2006) 10. Central Iran 53f 1.02 Ma'hood et al. (2009) 11. ...
The study area is located between latitudes 22.5° and 26° N and longitudes 85° and 88.3° E, and consists of composite batholithic complex of eastern Indian Shield. Several hot springs, shear zones, lineaments, faults, and numerous small hills have characterised the strange tectonic setting of the area. During 2007-08,160-local-earthquake events recorded by broadband instrument at Indian School of Mines, Dhanbad, India were analysed for studying the seismicity of the region. The region mainly documents small magnitude (Mw) earthquakes predominantly confined between 1.0 and 2.0. Earthquakes with Mw>2.0 are not rare, and even few with Mw>4.0 also occur occasionally. Coda Q was analysed based on single back-scattering model using seismograms filtered at frequency bands 1-5, 5-10, and 10-15 Hz for 20 events with less than 250-km epicentral distance and magnitude 1.7-4.2 first time for the eastern Indian Shield region. Very low coda Q estimated at all frequencies probably indicates higher heterogeneity or concentrated deformation in the eastern Indian Shield. Comparatively lower coda Q at higher frequency is apparently associated with higher heat-source zones. Several hot springs lying in the region presumably account for higher thermal regime and invariably support the ductile strain localisation along shear zones that allows reactivation of fractures and possibly triggers small magnitude earthquakes through brittle failure of rocks.
... It may be stated from the entire discussion that the study region accounts for moderate to higher attenuation of seismic shear wave. During worldwide comparison (Fig. 5), lesser attenuation relative to Eastern Canada (Chun et al. 1987;Shin and Herrmann 1987), Canadian Shield (Hasegawa 1985), Eastern United States (Gupta and McLaughin 1987), Central Appalachia (Shi et al. 1996), Gupta and Kumar (2002) 2. Sourashtra 170f 0.97 Sharma et al. (2012) 3. Kachchh 148f 1.01 Sharma et al. (2008) 4. Andaman 119f 0.8 Parvez et al. (2008) 5. Koyna 169f 0.77 Mandal and Rastogi (1998) 6. Garhwal Himalaya 110f 1.02 Gupta et al. (1995) 7. Indian Shield 508f 0.48 Singh et al. (1999) 8. Kumaun Himalaya 92f 1.07 Paul et al. (2003) 9. ...
... Jabalpur Region 339f 0.63 Singh et al. (2004) 11. NW Himalaya 158f 1.05 Kumar et al. (2005) 12. Central India 332f 0.59 Mandal et al. (2013) Shin and Herrmann (1987) 2. Canadian Shield 900f 0.2 Hasegawa (1985) 3. Eastern Canada 1100f 0.19 Chun et al. (1987) 4. Eastern United States 800f 0.32 Gupta and McLaughin (1987) 5. Central Appalachia 570f 0.46 Shi et al. (1996) 6. Adirondack Mountains 905f 0.4 Shi et al. (1996) 7. New England 460f 0.4 Pulli (1984) 8. Baltic Shield 125f 1.08 Kvamme and Havskov (1989) 9. Southern Italy 62.5f 0.7 Tuve et al. (2006) 10. Central Iran 53f 1.02 Ma'hood et al. (2009) 11. ...
We have analyzed 16 earthquake waveform data recorded during the period from 2006 to 2013 at broadband station lying at the premises of Indian School of Mines, Dhanbad in the Eastern Indian Shield region. Coda window lengths of 30, 40 and 50 s were selected after thorough analysis of the waveforms. The Coda Q (Qc) values were computed using single back scattered method. The earthquakes parameters were compiled from catalogue of Indian Meteorological Department (Nodal agency under Govt. of India for record keeping and data sharing), New Delhi. The estimated average Qc values for three coda windows 30, 40 and 50 s are Qc = 259.1f0.808, Qc = 275.9f0.764 and Qc = 397.1f0.651, respectively. The average Qc value estimated from the Qc values for the time windows 30, 40 and 50 s is found to be Qc = 313.2f0.73. Thus, the attenuation follows the power law relationships (e.g., Qc = Q0fn), and the moderate to higher values of frequency parameters (n) obviously show that the Qc value is a strong function of frequency. The increasing values of Q0 with increasing lapse time indicating the depth dependency of attenuation, and accounts for decreasing heterogeneity towards deeper level beneath the study area.
... In spite of the seismic activity and the heterogeneity of the medium, the level of the seismic wave attenuation in the area of the Middle Atlas is low. Usually, similar values of the Q-factor are observed for the tectonically stable areas such as the thick consolidated shields and cratons (the Canadian Shield, the Siberian Craton, the North Iberia, the North American Platform and others (Hasegawa 1985;Singh and Herrmann 1983;Pujades et al. 1990;Dobrynina et al. 2016). The obtained result is unexpected and in contrast with the data obtained in previous studies (Calvert et al. 2000). ...
The following study aims at investigating the 2D distribution of the seismic wave attenuation based on the quality factor of the seismic coda waves in the northern part of Morocco. In this regard, the waveforms of 66 local earthquakes have been analyzed. The waveforms were recorded from 26 broadband seismic stations deployed by the Scientific Institute of Rabat during 2008, through the different structural domains. The coda wave seismic quality factor (QC) has been extracted through the application of the back-scattering model proposed by Aki and Chouet (1975) using four central frequencies (1.5, 3, 6, and 12 Hz) and through four lapse time windows (30, 40, 50, and 60 s). Additionally, spatial distribution maps of the quality factor of the coda waves, for this region, were generated. The study area, based on the 2D maps of the quality factor, has revealed the existence of several stable anomalies of the QC values for all frequencies and for all windows used, Al-Hoceima and Nador regions for instance, and has shown that all territory under study can be divided into five different zones. The comparison of the spatial variations of the seismic wave attenuation, geological, and geophysical characteristics of the Northern Morocco shows that the seismic attenuation correlates with the seismic activity, the position of the fault zones, the heat flow, and the Cenozoic volcanism. Furthermore, the attenuation of the coda waves decreases with the lapse time window increasing (and accordingly with the depth of the seismic wave penetrating). Such behavior in the Q-factor may indicate that the upper part of the lithosphere is more heterogeneous compared to the lower layers. These results can be used not only for scientific research, but also in the practice domain for the calculation of the earthquake source parameters or in the mapping of seismic hazard.
... If it is assumed that waves propagate in uniform media, then the geometrical spreading parameter for body waves is given as R À1 , where R is the hypocentral distance, for distances \100 km (e.g., Aki 1980;Ib añez et al. 1990;Canas et al. 1991). For distances greater than 200 km, this parameter is assumed to be equal to R À0.5 , the theoretical value for surface waves in a half-space medium (e.g., Haswgawa 1985;Shin and Herrmann 1987). However, as propagation media are far from being uniform, especially in the short-distance range (local earthquakes), a rough approximation is to take a value of R À1 for this parameter. ...
In the present study, we have estimated the quality factor Coda-Q (Qc) using the single backscattering model for Mainland Gujarat region of Western Deccan Volcanic Province (DVP) India. The said region comes under seismic zone III as per seismic zonation map of India and is vulnerable for earthquakes of magnitude up to 6.0. Mainland Gujarat comprises of the eastern rocky highlands and western alluvial plains. The broadband waveforms of 80 local earthquakes (Mw 2.5–4.3) having depths in the range (2.0–34.0 km) recorded at eight stations of Mainland Gujarat have been used for the analysis. The average values of Qc for the lapse time windows of 20–90 s with standard error varies respectively from 113 ± 12 to 411 ± 37 at 2 Hz and 1008 ± 150 to 3600 ± 400 at 16 Hz, respectively. This suggests that the region is more attenuative and heterogeneous than the Kachchh and Saurashtra of DVP. The increase in ‘Qc’ values with lapse time displays the depth dependence of ‘Qc’ because of the fact that longer lapse time windows will sample larger area. We have compared the frequency-dependent relations for ‘Qc’ derived here with those of other parts of India and the World. The study is inevitable for the estimation of source parameters, thereby, evaluation of seismic hazard of the region.
... The dynamic ranges are excellent, being 96 and 108 db, respectively, at the stations deploying Mark I and Mark II outstation packages (Munro et al., 1984). The ECTN instrument response plots can be found in several recent articles (Hasegawa, 1985;Chun et al., 1987Chun et al., , 1989a) and hence are not reproduced here. Table 1 lists the 16 selected events, The magnitudes of these events, as determined by the Geophysics Division, Geological Survey of Canada, range from 3.1 to 5.4. ...
Station site effects, uncertainties in seismic source spectrum, and instrument response errors are among the well-known frequency-dependent contaminating factors that limit the reliability of short-period Q measurements of regional phases. For the Pn wave, a regional phase of importance for both magnitude determination and nuclear test ban verification, the problem is made worse by the added uncertainty of its geometric spreading function. For realistic earth models, the Pn geometric spreading function is likely to depart drastically from that expected of canonical head waves. The extent of this departure is sensitively dependent upon the regional crust/mantle structure, making geometric spreading assumption a conspicuous source of disagreement among the published Pn attenuation (QPn) estimates.
We describe a technique, referred to here as the extended reversed two-station method (RTSM), for simultaneous determination of QPn and geometrical spreading function. The formulation, being designed to bring about direct cancellation of the contaminating source, station and instrument effects, is a reliable tool for mapping the Pn propagation characteristics over continental paths, long and short.
The extended RTSM has been tested using Pn spectral amplitude data derived from seismic records of the Eastern Canada Telemetered Network (ECTN). We find the spreading rate coefficient n in the power-law representation of the geometric spreading (d−n, d being epicentral distance) to be frequency dependent, increasing from 1.11 at 1 Hz to 1.77 at 20 Hz. Our QPn model in eastern Canada takes the form of QPn = 189f0.87. The results from eastern Canada suggest that: (a) there exists a significant positive velocity gradient in the uppermost mantle (≧ 0.0037 sec−1); (b) the regionally recorded Pn waves are dominated by the superposition of a series of interfering diving waves bent by the velocity gradient and internally reflected at the underside of the Moho discontinuity; and (c) the very strong frequency-dependence of QPn we found in this study region may not be unique among low-attenuating shield and platform regions.
... Following Hasegawa (1985), we model measured amplitude spectra as ...
We discriminate upper-mantle earthquakes from crustal earthquakes based on the amplitude ratio of seismic waves Sn and Lg (‘Sn/Lg’), a prominent feature of regional seismograms that is visible to the naked eye. Crucially, our new method uses only the waveforms of the candidate earthquake, unlike previous methods to identify upper-mantle earthquakes that introduce potentially large errors by comparing hypocentral depths with independent measures of crustal thickness. Our synthetics show that the Love-wave higher modes that form individual Sn and Lg Airy phases on the transverse component are preferentially excited when the source is respectively below or above the Moho. We use three previously recognized mantle events from southern Tibet to validate our new approach and show that focal mechanism, intrinsic attenuation, geometrical spreading etc., can be ignored to first order. We then identify two new upper-mantle earthquakes in NW Tibet where, previously, only lower-crustal events had been reliably demonstrated, thereby showing this NW-Tibet lithosphere is seismogenic at all depths i.e. that upper-mantle and lower-crustal earthquakes co-exist. Our method has potential for expanding the global catalog of continental earthquakes reliably determined to be close above or close below the Moho.
... The obtained attenuation contours correlate with the crustal model proposed by Lizarralde et al., (2007) and Teske et al., (2014) and support the high attenuation of seismic energy observed along the gulf region. Also, the decrease in seismic velocity and high heat flow beneath the thin crust correlates with the high attenuation observed along the young plate boundary Teske et al., 2014;Vidales-Basurto et al., 2014;Lizarralde et al., 2007;Hasegawa 1985). These results also indicate that the seismic attenuation is decreasing towards the continental crust. ...
Se aplicó un esquema de inversión iterativo, inicialmente desarrollado por Hashida y Shimazaki (1984) y posteriormente modificado por Joshi et al., (2010), para estimar el factor de calidad de onda corta tridimensional, Qs (f), del centro-sur del Golfo de California, México. Es un área de 230 x 288 km que se divide en 108 bloques rectangulares de diferentes Qs (f). Se utilizó 25 terremotos bien ubicados registrados en tres estaciones de banda ancha de la red regional RESBAN operada por CICESE (Centro de Investigación Científica y de Educación Superior de Ensenada, Baja California) y tres Sismógrafos de Fondo Oceánico (OBS, por sus siglas en inglés) de un conjunto del Experimento del Fondo Oceánico del Mar de Cortés (SCOOBA, por sus siglas en inglés). Este conjunto de datos permitió obtener estimaciones de Qs (f) de diferentes bloques, utilizando el algoritmo de inversión modificado. El Qs (f) se obtuvo a varias frecuencias en el rango de 0,16 ~ 8,0 Hz. Se encontró que la estructura Qs estimada se correlaciona con los modelos geológicos y tectónicos de la región propuestos en estudios previos. Se obtuvo una relación regional dependiente de la frecuencia que utiliza todos los valores de 1944 del factor de calidad de la onda de corte a 18 frecuencias diferentes en todos los bloques y se puede aproximar mediante una función de la forma Qs (f) = 20 f 1.2. Esta relación es típica en una región tectónicamente activa con alta atenuación de onda S y es similar a las relaciones de atenuación reportadas por otros autores para la región del Valle Imperial, California.
doi: https://doi.org/10.22201/igeof.00167169p.2021.60.2.2053
... The Q-values generally increase with frequency and are mostly in the range of 4-14. An increasing trend of frequency-dependent Q-values has been widely observed in previous studies (e.g., Aki and Chouet, 1975;Hasegawa, 1985;Mayeda et al., 1992;Erickson et al., 2004). The overall increase of Q-values with distances from the road to receivers is consistent with the proximity of the road to the main fault trace and core damage zone at the SGB site Qin et al., 2018;Share et al., 2020). ...
Correct identification and modeling of anthropogenic sources of ground motion are of considerable importance for many studies, including detection of small earthquakes and imaging seismic properties below the surface. To understand signals generated by common vehicle traffic, we use seismic data recorded by closely spaced geophones normal to roads at two sites on San Jacinto fault zone. To quantify the spatiotemporal and frequency variations of the recorded ground motions, we develop a simple analytical solution accounting for propagation and attenuation of surface waves. The model reproduces well-observed bell-shaped spectrograms of car signals recorded by geophones close to roads, and it can be used to estimate frequency-dependent Q-values of the subsurface materials. The data analysis indicates Q-values of 3–40, for frequencies up to 150 Hz for road-receiver paths at the two examined sites. The derived Q-values are consistent with attenuation factors of surface waves previously obtained with other methods. The analytical results and analysis procedure provide a highly efficient method for deriving Q-values of shallow subsurface materials.
... Further, the regional and teleseismic tomographic study detected a low P-wave velocity extending from upper mantle to 600 km depth underlying the Kachchh rift zone (KRZ), Gujarat (Kennett and Widiyantoro 1999). Recently, a joint inversion study of P-receiver functions and surface wave group velocity dispersion data imaged several patches of low Singh and Hermann (1983) Central USA 1000 0.20 Singh and Hermann (1983) Canadian Shield 900 0.20 Hasegawa (1985) (Mandal 2012). Now, we know that if attenuation is entirely intrinsic, then coda Q c will be very sensitive to temperature perturbation and liquid content within the medium (Gao 1992). ...
Abstract We study the attenuation of seismic wave energy in the aftershock zone of the 2001 Bhuj earthquake using high-quality (S/N ratio C 2.0) data of 181 aftershocks recorded on eleven three-component broadband seismograph stations. The moment magnitudes and focal depths of the selected aftershocks vary from 2.7 to 4.8 and 2 to 50 km, respectively. The three-component broadband data of these selected aftershocks are used to estimate a new frequency-dependent coda-Q (Qc) relation (Qc = Q0 fn) in the frequency range 1.5–15 Hz, for the seismically active Kachchh rift zone, Gujarat. We have used single backscattering model to estimate frequency-dependent values of coda Qc at central frequencies 1.5, 3, 6, 9, 12 and 15 Hz through eight lapse time windows (tL) from 20 to 90 s starting at double the travel time of S-waves. The average frequency-dependent Qc relationship in the range of 1.5–15 Hz for the Kachchh region is estimated to be (82 ± 1) f(1.12±0.01), (121 ± 1) f(1.03±0.01), (154 ± 1) f(0.96±0.01), (181 ± 1) f(0.91±0.01), (207 ± 1) f(0.85±0.01), (239 ± 1) f(0.79±0.01), (271 ± 1) f(0.73±0.01) and (304 ± 1) f(0.68±0.01), for lapse time windows of 20, 30, 40, 50, 60 70, 80 and 90 s, respectively. For tL = 20–50 s, we estimate Qc = 52–163 and n = 0.87–1.18, while for tL = 60–90 s, we find Qo = 128–486 and n = 0.45–1.05. These estimates of Qo and n are found to be in good agreement with the estimates of Qo and n for highly heterogeneous and seismically active regions around the world. We also estimate actual hazard parameters, viz. the extinction distances (Le) and anelastic attenuation coefficients (c), by assuming that attenuation is entirely intrinsic. Le estimates vary from 56 to 99 km, while the corresponding c estimates range from 0.009 to 0.0054 km-1. The estimated Qo values at locations in the Mesozoic Kachchh rift basin are found to be low in comparison with the areas at a distance from it. This could be attributed to the fact that seismic waves being highly scattered for paths through the seismically active and fractured zone, but less scattered outside the aftershock zone. This model also gets support from the presence of 1- to 2-km-thick top low-velocity Quaternary sediments, and a large volume of crustal and upper mantle metamorphic fluids/carbonatite melts underlying the central rift basin. We also propose that the Qc relations developed in this study could be useful for predicting ground motion in the region.
... Further, the regional and teleseismic tomographic study detected a low P-wave velocity extending from upper mantle to 600 km depth underlying the Kachchh rift zone (KRZ), Gujarat (Kennett and Widiyantoro 1999). Recently, a joint inversion study of P-receiver functions and surface wave group velocity dispersion data imaged several patches of low Singh and Hermann (1983) Central USA 1000 0.20 Singh and Hermann (1983) Canadian Shield 900 0.20 Hasegawa (1985) (Mandal 2012). Now, we know that if attenuation is entirely intrinsic, then coda Q c will be very sensitive to temperature perturbation and liquid content within the medium (Gao 1992). ...
... Numerically, the active tectonic regions have Q 0 values that are less than 200 (Q 0 < 200), while the coefficient of the frequency dependency is more than 0.8 (n > 0.8) (Aki and Chouet, 1975;Azguet et al., 2019;Gupta et al., 1995;Havskov et al., 1989;Woodgold, 1994). On the other hand, the Q 0 values for inactive tectonic regions are higher than 600 (Q 0 > 600) and for n is lower than 0.5 (n < 0.5) (Atkinson, 2004;Hasegawa, 1985). For the regions that are regarded as a moderate tectonic areas, Q 0 values are set between 200 and 600 (200 > Q 0 > 600) and n between 0.4 and 0.7 (0.4 < n < 0.7) (Kumar et al., 2007;Pulli, 1984;Roecker et al., 1982;Sedaghati and Pezeshk, 2016). ...
... Coda Q helps to understand the tectonic activities, where stable region is characterized by high-Q value and seismically active region characterized by low-Q value (Pujades et al., 1990;Herrmann, 1980). Diverse tectonic regions of different parts of the world revealed different average attenuation relationship, such as, South India, Q = 460f 0.83 (Rao et al., 1998); New England, Q = 460f 0.40 (Pulli, 1984); Eastern North America, Q = 680f 0.36 (Atkinson and Boore, 1995); North Iberia Q = 600f 0.45 (Pujades et al., 1997); Indian Shield, Q = 800f 0.42 ; NE U.S., Q = 900f 0.35 (Singh and Herrmann, 1983); Central U.S., Q = 1000f 0.20 (Singh and Herrmann, 1983); Canadian Shield, Q = 900f 0.20 (Hasegawa, 1985) and Central Mississippi Valley (CENA), Q = 210f 0.78 (Dwyer et al., 1984); Aleutian Islands, Q = 214f 1.05 (Scherbaum and Kisslinger, 1985); Koyna, India, Q = 96f 1.09 (Gupta et al., 1998); Bhuj, India, Q = 102f 0.98 (Mandal et al., 2004); Western U.S., Q = 150f 0.40 (Singh and Herrmann, 1983); and for NW Himalaya, Q = 126f 1.12 (Vandana et al., submitted for publication). Moreover, the seismic coda wave attenuation provided significant information and a great help in understanding of many geophysical mechanisms related to intrusion and associative processes with rock materials (e.g., Guo et al., 2009). ...
... In other words, there is a correlation between Q values with seismicity of a region. For seismically inactive regions, high Q 0 values and low-frequency-dependent power values (Q 0 > 600, η < 0.4) have been reported (Singh and Herrmann 1983;Hasegawa 1985;Pujades et al. 1990;Atkinson and Mereu 1992;Atkinson 2004). On the other hand, low Q 0 values and high-frequency-dependent power values (Q 0 < 200, η > 0.7) have been observed for tectonically active regions (Aki and Chouet 1975;Havskov et al. 1989;Woodgold 1994;Hellweg et al. 1995;Giampiccolo et al. 2004;Rahimi and Hamzehloo 2008;Padhy et al. 2011;Shengelia et al. 2011;Sertçelik 2012;de Lorenzo et al. 2013;Ma'hood 2014;Farrokhi et al. 2015;Singh et al. 2019). ...
In this study, we evaluate the body and coda wave attenuation characteristics within Kyrgyzstan and Tajikistan as a part of central Asia. The selected database consists of 354 broadband seismograms from 179 local earthquakes recorded by 24 different stations within the period of 2015 through 2018. First, coda Q has been inferred for different coda window lengths of 20, 30, 40, and 50 sec using the single-backscattering interpretation. The coda Q values increase by increasing the coda window length. We show that coda attenuation properties in central Asia are better modeled by multiple-scattering and surface wave regimes for long distance records without invoking any depth dependence of the attenuation properties in the crust. Furthermore, standard errors and convergence of different components’ QCindicate that we can fit envelope records of coda waves much better using a coda window length of 50 sec. Therefore, we evaluate average coda quality factor functions as QC = 261 f 0.601 and QC = 219 f 0.633 assuming multiple-scattering and surface-wave regimes for a coda window length of 50 sec in the frequency range of 1 to 20 Hz for distances up to 200 km. We also show that the source to site distance of records has a significant impact on coda Q estimates. For a shorter distance range up to 100 km, attenuation attributes of central Asia are better captured by a single-scattering model. We reevaluate the average coda quality factor function as QC= 222 f0.692 assuming a single-backscattering model for a coda window length of 50 sec in the frequency range of 1 to 20 Hz for distances up to 100 km. Moreover, we determine QP = 158 f 0.706 and QS = 152 f 0.856with a geometrical spreading function of R-1using the multiple-station coda normalization method.
... Comparison with Previous Studies. In this section, we summarize the many studies that have been conducted to estimate crustal attenuation within this region using different approaches 3,4,11,14,25,34,37,[58][59][60][61][66][67][68][69][70][71] , and compare their attenuation estimates to our results. ...
We perform Q Lg tomography for the northeastern part of North America. Vertical broadband seismograms of 473 crustal earthquakes recorded by 302 stations are processed to extract the Lg amplitude spectra. Tomographic inversions are independently conducted at 58 discrete frequencies distributed evenly in log space between 0.1 and 20.0 Hz. This relatively large dataset with good ray coverage allows us to image lateral variation of the crustal attenuation over the region. Obtained Q Lg maps at broadband and individual frequencies provide new insights into the crustal attenuation of the region and its relationship to geological structures and past tectonic activity in the area. The Q Lg shows more uniform values over the older, colder, and drier Canadian Shield, in contrast to higher variations in the younger margins. Results confirm the correlation of large-scale variations with crustal geological features in the area. Existence of low-velocity anomalies, thick sediments, volcanic rocks, and thin oceanic crust are potential sources of observed anomalies. The mean Q values are inversely correlated with average heat flow/generation for main geological provinces.
... Different studies generally show low values of Q 0 (less than 200) for tectonically and seismically active regions such as, Washington State (Q C =63f 0.97 , Havskov et al. [11]), NW Himalayan region (Q C =158f 1.05 , Kumar et al. [22]), Koyna (Q C =169f 0.77 , Gupta et al. [16]) and East Central Iran (Q C =101f 0.94 , Mahood and hamzehloo [23]). The larger Q 0 values of more than 200, have been observed for moderate and inactive or stable regions such as New England (Q C =460f 0.4 , Pulli [15]), Canadian Sheild (Q C =900f 0.35 , Hasegawa [24]), and Central USA(Q C =1000f 0.20 , Singh and Herrmann [5]). The quality factor, Q 0 and frequency dependent exponent, n, for Hormuzgan region correlate well with the values found in tectonically active regions. ...
The attenuation of Coda waves (Qc) of local earthquakes, has been estimated for Hormuzgan region in south of Iran. In this research, the recordings of 200 local earthquakes on the Bandar-Abbas (BNDS) station of the Iranian National Seismic Network (INSN), have been used. These events were recorded during June 2004 until August 2009 with magnitudes of between 2.5 and 5.1 (ML), epicentral distance of between 15 and 100 km and average focal depth of about 15 km. The Qc values were computed at seven central frequencies of 1.5, 3.0, 4.5, 6.0, 9.0, 12.0 and 18.0 Hz through five lapse time windows from 20 to 60 s starting at double the time of the primary S-wave from the origin time using the time-domain Coda-decay method of a single backscattering model. The variation of the quality factor, Qc, was estimated at different lapse time windows to observe its effect with depth. The estimated frequency dependent relationship of Qc varies from Qc=(61±9)f^(1.09±0.19) at 20 s to Qc=(132±28)f^(0.90±0.10) at 60 s lapse times window. The average Qc values and frequency dependent relationships correlate well with a highly tectonically active region.
... Thus, the Lg wave propagates efficiently over continental paths, having been observed at distances up to 30 • in the Canadian Shield (Hasegawa 1985), which have sufficient crustal thickness. In contrast, very thin oceanic crust (<10 km) is unable to maintain these modes (e.g. ...
Lg attenuation and site responses in Northeast (NE) China are estimated by implementing the Reverse Two Station Method (RTSM) at narrow band central frequencies of 0.5, 1.0, 2.0 and 3.0 Hz using 453 earthquakes recorded by 201 seismic stations deployed in the region from 1995 to 2013. The RTSM has the advantage of removing source and site effects without requiring a priori models. Tomographic images produced at a resolution of 2 • × 2 • at all frequencies exhibit a high degree of lateral variation of Lg attenuation in NE China. The Great Xing'an, Lesser Xing'an and Songen-Zhangguangcai Ranges show Q values above 400 at all frequencies. At central frequencies of 0.5 and 1 Hz, Sanjiang Basin Songliao Basin, Erlian Basin and Hailar Basin consistently show Q values lower than 400. Holocene and Pleistocene volcanoes, including the Wudalianchi and Jingpuhi volcanic fields, also appear as regions of low Q (<400) at 0.5 and 1 Hz and at higher frequencies the effects of volcanoes diminish. At high frequencies (≥2 Hz), the sedimentary basins show Q values higher than 400 and overall Q values increase with frequency in NE China, thus obeying a power-law frequency dependence. A linear regression of frequencies in the range of 0.25-4.5 Hz results in the parameters describing the power-law frequency dependence of the region, with an average Q 0 value of 428 and a frequency-dependent factor (η), describing the strength of dependence, of 0.68. Overall, Lg attenuation in NE China appears to be due to thick late Cretaceous sediments, Holocene and Pleistocene volcanism, moderate to high heat flow, partial melts and variation in the thickness of the crustal wave guide. The site responses calculated at 0.5, 1.0, 2.0 and 3 Hz show a high degree of lateral variation as well as variation with frequency in NE China. At 0.5 and 1.0 Hz, the Great Xing'an and Lesser Xing'an Ranges show deamplification while the Hailar, Erlian and southern Songliao basins and the Songen-Zhangguangcai Range show amplification. At higher frequencies (≥2 Hz), the pattern nearly reverses, with deamplification east of the Songliao Basin and amplification to the west of the Basin. The deamplification observed east of the Songliao Basin could be caused by basaltic lava flows resulting from Cenozoic volcanism in the region.
... Although regional attenuation in eastern North America has been studied using Lg waves and seismic coda waves (e.g. Nuttli, 1973;Singh and Herrmann, 1983;Hasegawa, 1985;Shin and Herrmann, 1987), this type of study yields little information about nearsurface contributions to attenuation (Hough et al., 1988). Studies of Lg and coda waves argue for high Q in eastern North America, with typical values of 800-1000 at 1 Hz (Singh and Heiimann, 1982;Shin and Herrmann, 1987), and for consistently lower attenuation than in western North America. ...
We present analysis of a magnitude 3.5 event which occurred at 9 km epicentral distance from a digital strong motion instrument operated by the National Center for Earthquake Engineering Research: 1) the S-wave spectra can be interpreted in terms of a simple omega-squared source spectrum and frequency-independent attenuation, 2) there is the suggestion of a poorly-resolved resonance in the P-wave spectrum, and perhaps most importantly, 3) the apparently simple S-wave spectra can be fit almost equally well with a surprisingly wide range of seismic corner frequencies, from roughly 5 to 25 Hz. -from Authors
... Shield (Hasegawa ,1985), Iberian Peninsula-Spain (Pujades ,1990), southeastern Canada In this work, coda-Q (Q C ) has been estimated for the Kopili fault zone using a single back-scattering model of S-coda envelopes. Based on the analysis the following inferences can be made. ...
Kopili fault has been experiencing higher seismic and tectonic activity during the recent years. These kind of active tectonics can be inspected by examining coda-wave attenuation and its dependence with frequency. Exploiting single back-scattering model, we have endeavored to measure coda Q and its associated parameters such as frequency dependent factor (n) and attenuation coefficient (γ) covering seven lapse-time windows spanning from 30 to 90 sec and central frequencies 1.5, 3.5, 6, 9 and 12 Hz. The average estimated values of QC increases with frequency and lapse time window from 114 at frequency 1.5Hz to 1563 at frequency 12Hz for 30sec window length, and from 305 at frequency 1.5Hz to 2135 at frequency 12Hz for 90sec window length. The values of Q0 and n are also estimated for the entire Kopili fault zone. For this study region, the Q0 values vary from 62 to 348 and n varies from 0.57 to 1.51 within the frequency range 1.5 to 12 Hz. Furthermore, depth variation of attenuation of this region reveals that there is velocity anomaly at depth 210-220 km as there arises sharp changes in γ and n which are supported by available data, reported by other researcher for this region. Finally, we have tried to separate the intrinsic and scattering attenuation for this area. It is observed that the entire region is dominated by mainly scattering attenuation, but we can see an increase in intrinsic attenuation with depths in two stations namely TZR and BKD. Furthermore, the obtained results are comparable with the available global data.
... As we can see from Figs. 5 and 9a, much of the Australian continent has relatively high Lg Q values, though there are regions with quite low Q. The Q values for most Proterozoic and Paleozoic regions in Australia, such as the Amadeus Basin and Georgetown inlier, are comparable to the Lg Q of the Canadian Shield, which is 900 at 1 Hz (Hasegawa, 1985), the central United States with Q values larger than 1052 above 1.5 Hz (Benz et al., 1997), the stable part of South America whose Q values range between 550 and 1000 (De Souza and Mitchell, 1998) as well as stable portions of Eurasia with values larger than 600. The ...
The dominant high-frequency component of ground motion for most seismic events in Australia comes from the crustal Lg phase that can commonly propagate efficiently to considerable distances across the continent. Using results from recent tomography for the attenuation of Lg, we are able to build the pattern of transmission of ground motion from events within the continent. The effects are readily displayed in terms of a distribution of effective magnitude. The same approach can also be used to look at the cumulative effects across the continent from 1840 to date as a useful complement to other ways of assessing earthquake potential.
... As we can see from Figs. 5 and 9a, much of the Australian continent has relatively high Lg Q values, though there are regions with quite low Q. The Q values for most Proterozoic and Paleozoic regions in Australia, such as the Amadeus Basin and Georgetown inlier, are comparable to the Lg Q of the Canadian Shield, which is 900 at 1 Hz (Hasegawa, 1985), the central United States with Q values larger than 1052 above 1.5 Hz (Benz et al., 1997), the stable part of South America whose Q values range between 550 and 1000 (De Souza and Mitchell, 1998) as well as stable portions of Eurasia with values larger than 600. The ...
We estimate the Lg-wave quality factor (Q) across the Australian continent from vertical-component Lg waveforms.
A tomographic inversion is performed to construct an Lg attenuation model for 58 frequencies between
0.05 and 10.0 Hz. The available spatial resolution is approximately 1.5° × 1.5° for the 0.5–2.0 Hz band. At
1.0 Hz, the Lg-wave Q over the whole island continent varies from 50 to 1250 with an average value of 850.
Significant regional variations in the Lg-wave Q images tie well with many geological features and boundaries in
Australia. The cratons in western, northern and southern parts of Australia usually have higher Q values
(700–1250), while the volcanic regions, sedimentary basins and orogenic areas in eastern Australia are characterized
by increased attenuation (lower Q values, 50–650). We determine the frequency-dependent Q of Lg
waves for different blocks across Australia, and find the frequency dependence of Q is much more complex than
the traditional single power law representation. When combined with the assumed geometrical spreading relation,
the Lg Q maps provide a new way of assessing potential ground motion across the continent for any event
location.
... Coda waves are backscattered body waves and low frequency surface waves that sample a wide range of focal sphere (Frankel, 2015), and Lg waves are reflected several times within the guide path. Thus, the common feature of both Lg and coda waves is that they both sample the entire propagation path (Hasegawa, 1985). ...
Unique properties of coda waves are employed to evaluate the frequency dependent quality factor of Lg waves using the coda normalization method in the New Madrid seismic zone of the central United States. Instrument and site responses are eliminated and source functions are isolated to construct the inversion problem. For this purpose, we used 121 seismograms from 37 events with moment magnitudes, M, ranging from 2.5 to 5.2 and hypocentral distances from 120 to 440 km recorded by 11 broadband stations.
A singular value decomposition (SVD) algorithm is used to extract Q values from the data, while the geometric spreading exponent is assumed to be a constant. Inversion results are then fitted with a power law equation from 3 to 12 Hz to derive the frequency dependent quality factor function. The final results of the analysis are QV Lg ( f ) = (410 ± 38) f 0.49 ± 0.05 for the vertical component and QH Lg ( f ) = (390 ± 26) f 0.56 ± 0.04 for the horizontal component, where the term after ± sign represents one standard error. For stations within the Mississippi embayment with an average sediment depth of 1 km around the Memphis metropolitan area, estimation of quality factor using the coda normalization method is not well-constrained at low frequencies (f < 3 Hz). There may be several reasons contributing to this issue, such as low frequency surface wave contamination, site effects, or even a change in coda wave scattering regime which can exacerbate the scatter of the data.
... Several studies have examined eastern NAM decay of Lg waves, the multiply-reflected phase that dominates the high-frequency ground motions in continental crustal environments at distances of 100-1000 kilometers. Typically, a Q =Q0 f ° is assumed, with a between 0 and 1 (Chun et al., 1988;Shin and Herrmann, 1987;Hasegawa, 1985;Gupta and McLaughlin, 1987;Nuttli, 1973;Street, 1976). Values of Qo for eastern NAM generally range from 800 to 1100 and values of a are in the range 0.2-0.5. ...
A key element in the assessment of seismic hazard is the estimation of how energy propagation from a given earthquake is affected by crustal structure near the receiver and along the more distant propagation path. Data from a variety of sources in eastern North America recorded at epicentral distances of a few to 800 km are presented and systematic features are characterized and interpreted. Site effects have been classically considered in terms of amplification either within a sediment-filled valley or from a single topographic feature. Evidence is presented of high frequency (5-30 Hz) resonances observed in hard-rock recordings of both body waves and Lg waves, and it is suggested that site effect should be expanded regionally to include structural and topographic information over sufficiently large areas to include several wavelengths of any features that may interact with seismic waves in the frequency range of interest. A fundamental difference between eastern and western North America spectra may stem from a combination of differences in the character of topography and near-surface structure. A preliminary analysis of topographic data from the Adirondack Mountains in New York demonstrates the existence of characteristic length scales on the order of up to 1-3 kilometers. Features with these length scales will effectively scatter energy at frequencies in the 1 to 10 Hz range. -from Authors
... Instead of using a specific study, the median was used. [Hasegawa 1985;Shin and Hermann 1987;Woodgold 1990;). These studies partly include an investigation area within the APP region. ...
... For tectonically active areas, low Q 0 values and high values of the frequency-dependent power η (Q 0 < 200, η > 0:7) have been reported (Aki and Chouet, 1975;Havskov et al., 1989;Woodgold, 1994;Hellweg et al., 1995;Giampiccolo et al., 2004;Rahimi and Hamzehloo, 2008;Padhy et al., 2011;Shengelia et al., 2011;Sertçelik, 2012;de Lorenzo et al., 2013;Ma'hood, 2014;Farrokhi et al., 2015). On the other hand, for tectonically inactive areas, high Q 0 values and low values of the frequency-dependent power η (Q 0 > 600, η < 0:4) have been acquired (Singh and Herrmann, 1983;Hasegawa, 1985;Pujades et al., 1990;Atkinson and Mereu, 1992;Atkinson, 2004). Finally, moderate values of Q 0 and η (200 < Q < 600, 0:4 < η < 0:7) have been obtained for regions between active and inactive areas considered as moderately active regions (Roecker et al., 1982;Pulli, 1984;Patanjali Kumar et al., 2007). ...
Using the single backscattering method, coda quality factor functions through coda window lengths of 20, 30, 40, 50, and 60 sec have been estimated for the New Madrid seismic zone (NMSZ). Furthermore, geometrical spreading functions for distances less than 60 km have been determined in this region at different center frequencies exploiting the coda normalization method. 284 triaxial seismograms with good signal to noise ratios (SNR > 5) from broadband stations located in the NMSZ. The database consisted of records from 57 local earthquakes occurring during the period of 2000 to 2009, with moment magnitudes of 2.6 to 4.1, and hypocentral distances less than 200 km.
Q-factor values were evaluated at five frequency bands with central frequencies of 1.5, 3, 6, 12, and 24 Hz. Vertical components were utilized to estimate vertical coda Q-factor values. Horizontal coda Q-factor values were determined using the average amount of the Q-factor values estimated from the both direction of horizontal components. The coda Q-factor increases with increasing of the coda window length implying that with increasing the depth, the coda Q-factor increases. The intermediate values of the Q-factor and intermediate values of the frequency dependency indicate the Earth’s crust beneath the entire NMSZ region is tectonically a moderate region with a moderate to relatively high degree of heterogeneities.
The geometrical spreading factors of S-wave amplitudes are frequency dependent and determined to be -1.271, -1.182, and -1.066 for center frequencies of 6, 12, and 24 Hz, respectively, at hypocentral distances of 10 to 60 km. The geometrical spreading for lower frequencies are not recommended to use due to the greater impact of the radiation pattern and directivity effect on low frequencies as well as the greater sensitivity of bandpass filtered seismograms of small earthquakes to the noise in low frequencies.
... Further, the regional and teleseismic tomographic study detected a low P-wave velocity extending from upper mantle to 600 km depth underlying the Kachchh rift zone (KRZ), Gujarat (Kennett and Widiyantoro 1999). Recently, a joint inversion study of P-receiver functions and surface wave group velocity dispersion data imaged several patches of low Singh and Hermann (1983) Central USA 1000 0.20 Singh and Hermann (1983) Canadian Shield 900 0.20 Hasegawa (1985) Fig . (Mandal 2012). ...
We study the attenuation of seismic wave energy in the aftershock zone of the 2001 Bhuj earthquake using high-quality (S/N ratio ≥ 2.0) data of 181 aftershocks recorded on eleven three-component broadband seismograph stations. The moment magnitudes and focal depths of the selected aftershocks vary from 2.7 to 4.8 and 2 to 50 km, respectively. The three-component broadband data of these selected aftershocks are used to estimate a new frequency-dependent coda-Q (Q
c) relation (Q
c = Q
0f
n
) in the frequency range 1.5–15 Hz, for the seismically active Kachchh rift zone, Gujarat. We have used single backscattering model to estimate frequency-dependent values of coda Q
c at central frequencies 1.5, 3, 6, 9, 12 and 15 Hz through eight lapse time windows (t
L) from 20 to 90 s starting at double the travel time of S-waves. The average frequency-dependent Q
c relationship in the range of 1.5–15 Hz for the Kachchh region is estimated to be (82 ± 1) f
(1.12±0.01), (121 ± 1) f
(1.03±0.01), (154 ± 1) f
(0.96±0.01), (181 ± 1) f
(0.91±0.01), (207 ± 1) f
(0.85±0.01), (239 ± 1) f
(0.79±0.01), (271 ± 1) f
(0.73±0.01) and (304 ± 1) f
(0.68±0.01), for lapse time windows of 20, 30, 40, 50, 60 70, 80 and 90 s, respectively. For t
L = 20–50 s, we estimate Q
c = 52–163 and n = 0.87–1.18, while for t
L = 60–90 s, we find Q
o = 128–486 and n = 0.45–1.05. These estimates of Q
o and n are found to be in good agreement with the estimates of Q
o and n for highly heterogeneous and seismically active regions around the world. We also estimate actual hazard parameters, viz. the extinction distances (L
e) and anelastic attenuation coefficients (γ), by assuming that attenuation is entirely intrinsic. L
e estimates vary from 56 to 99 km, while the corresponding γ estimates range from 0.009 to 0.0054 km−1. The estimated Q
o values at locations in the Mesozoic Kachchh rift basin are found to be low in comparison with the areas at a distance from it. This could be attributed to the fact that seismic waves being highly scattered for paths through the seismically active and fractured zone, but less scattered outside the aftershock zone. This model also gets support from the presence of 1- to 2-km-thick top low-velocity Quaternary sediments, and a large volume of crustal and upper mantle metamorphic fluids/carbonatite melts underlying the central rift basin. We also propose that the Q
c relations developed in this study could be useful for predicting ground motion in the region.
... We also calculate ground motions using the conventional assumption of a single direct ray with 1/R geometric spreading and Q =90140.2 (Hasegawa, 1985). In this case, R is the distance from each subfault to the site. ...
Seismic hazard is calculated for a grid of sites on the Mississippi embayment and adjacent areas. The seismic zonations, seismicity parameters, and maximum magnitudes for these calculations were synthesized from the EPRI (Electric Power Research Institute) and LLNL (Lawrence Livermore National Laboratory) interpretations, augmented by information from recent relevant studies. Attenuation functions developed for this study include the effects of source size and crustal structure. The soil amplification factors include the effects of surficial geology, soil-column thickness, and soil nonlinearity.
Seismic hazard maps, including the effect of site conditions, are presented for spectral accelerations at 1 and 10 Hz and for peak acceleration, for average return periods of 100, 500, and 1000 years.
These maps show significantly lower ground-motion amplitudes than those reported by Algermissen et al. (1991). Because of these large differences, it is suggested that code- development decisions be made after consideration of both studies.
... The method applied, together with the dis- tance range and frequencies used is also indicated. Table 2 shows that tectonically active regions are related to low Lg Q values (e.g., Ford et al., 2008;Ottemöller, 2002;Ottemöller et al., 2002;Ojeda and Ottemöller, 2002;Ferdinand, 1998;Benz et al., 1997;Paul et al., 1996;Akinci et al, 1995;Chávez and Priestley, 1986) whereas more stable tectonic areas are associated with high Lg Q (e.g., Hasegawa, 1985;Chun et al., 1987;Shi et al., 1996;Chung and Lee, 2003;Singh et al., 2004;McNamara et al., 2014;Mousavi et al., 2014). Intermediate values of Lg Q and frequency-dependent exponent η correlate well with areas of moderate seismicity such as Xinjiang and adjacent regions ( Zhou et al., 2011), North Korea ( Chun et al., 2009) and South Africa ( Frankel et al., 1990). ...
... Canadian Shield 900 0.35 Hasegawa (1985) Washington State 63 0.97 Havskov et al. (1989) S ...
Seismic wave attenuation is one of the most important parameters that reflect characteristics of the medium traversed by the seismic waves. This parameter is essential for many studies such as determining earthquake source parameters, predicting earthquake strong ground motion, monitoring nuclear explosions and estimating seismic hazard. Since 1995, several region-specific attenuation relations have been developed for the Indian regions, but no such relation is available for the Bilaspur region of the Himachal Lesser Himalaya for the want of data. A six-station local seismological network, deployed in the environs of Koldam site, provided digital recordings of 41 local events occurred in the region from May 2013 to March 2014. This data set has been used to develop the attenuation relations for the region. Majority of the events occurred in the Himachal Lesser Himalaya between the main boundary thrust and the main central thrust. All events have epicentral distances <100 km and magnitudes between 0.5 and 2.9. Adopting the single backscattering model of Aki and Chouet (J Geophys Res 80:3322–3342, 1975), coda-Q (Q
c) of the region has been estimated in lapse time windows of 20, 30 and 40 s, respectively. For 30-s lapse time window, the attenuation follows the relation Q
c (f) = (70.3 ± 20.27) f
(1.23±0.05) for the region. The observed Q
c relation is compared with similar relations for seismically active Indian regions and some of the globally available relations. It is found that the average variation of Q
c for the Bilaspur region is very close to Amazon Craton (Brazil) due to similar lithologic setup. The variation of ‘Q
0’ and ‘n’ values indicates that the region is highly heterogeneous and seismically active. The region is more heterogeneous near the surface as compared to depth. The estimated Q
c relations can be utilized for computing source parameters of the local earthquakes and for seismic hazard assessment for the Bilaspur region of Himachal Lesser Himalaya.
... Early determinations of Q Lg , after correcting for wave-front spreading, compared observed attenuation with distance with theoretically predicted attenuation for the Lg phase and chose the theoretical curve (predicted by selected values of Q o and η) which agreed best with observations (e.g. Nuttli, 1973;Street, 1976;Bollinger, 1979;Hasegawa, 1985;Campillo et al., 1985;Chavez and Priestley, 1986;Chun et al., 1987). Benz et al. (1997) ...
We present a review of our knowledge of the nature and distribution of attenuation in the Earth, with an emphasis on progress in the last 10 years. We discuss frequency dependence of the quality factor Q in the Earth, 1-D profiles and lateral variations in the crust and mantle, as well as the attenuation structure in the inner core. Much progress has been made recently in characterizing the lateral variations of attenuation in the crust and their relations to tectonics. Characterizing the nature and distribution of attenuation deeper in the Earth is still hampered by the need to separate elastic and anelastic effects on seismic-wave amplitudes. Nevertheless, consistent and robust features are emerging in recent tomographic studies of attenuation in the upper 200-300km of the mantle, which show that, in this depth range, lateral variations in attenuation are correlated with those in seismic velocities and with tectonics. This correlation fades out in the transition zone, where shear attenuation distribution bears more resemblance to velocity structure in the lowermost mantle. An unresolved issue is still a 20% discrepancy between the measurements of fundamental mode Rayleigh waves obtained using a propagating wave versus a normal mode approach. Regional studies of attenuation confirm the relation of Q with tectonics in the upper mantle, and very strong lateral variations in subduction zone areas. In the inner core, recent studies have confirmed the increase of Q with depth, and have found an intriguing hemispherical variation in Qα at the top of the inner core. Much of the attenuation in the inner core appears to be due to scattering.
... Further, the regional and teleseismic tomographic study detected a low P-wave velocity extending from upper mantle to 600 km depth underlying the Kachchh rift zone (KRZ), Gujarat (Kennett and Widiyantoro 1999). Recently, a joint inversion study of P-receiver functions and surface wave group velocity dispersion data imaged several patches of low Singh and Hermann (1983) Central USA 1000 0.20 Singh and Hermann (1983) Canadian Shield 900 0.20 Hasegawa (1985) (Mandal 2012). Now, we know that if attenuation is entirely intrinsic, then coda Q c will be very sensitive to temperature perturbation and liquid content within the medium (Gao 1992). ...
... Attenuation has also been interpreted in terms of Q models which depend both on frequency and on depth for surface waves (Mitchell, 1980(Mitchell, , 1981 and for body waves (Thouvenot, 1983). The method has also been used to study the attenuation of Lg waves, and many studies have reported Q = Qo[ a (Nuttli, 1973(Nuttli, , 1978(Nuttli, , 1980(Nuttli, , 1986Street, 1976;Bollinger, 1979;Dwyer et al., 1983;Hasegawa, 1985;Campillo et al., 1985;Chavez and Priestley, 1986). These studies have not examined the depth dependence of Q, although Herrmann and Kijko (1983) observed that the depth dependence is poorly resolved when Q is weakly dependent on frequency. ...
... This suggests that the ground motions at hard-rock sites in Delhi for earthquakes in the Chamoli region are better explained by the attenuation function derived for the Himalayan arc. This is Singh et al. (1999)] with those of the tectonically similar eastern North America [line 2: eastern Canada, Q(f ) ס 500f 0.65 , Shin and Herrmann (1987); line 3: Canadian shield, Q(f ) ס 900f 0.2 , Hasegawa (1985); line 4: eastern Canada, Q(f ) ס 1100f 0.19 , Chun et al. (1987); line 5: eastern United States, Q(f ) ס 800f 0.32 , Gupta and McLaughlin (1987); line 6: central Appalachia, Q(f ) ס 570f 0.46 , Shi et al. (1996); line 7: Adirondack Mountains, Q(f ) ס 905f 0.40 , Shi et al. (1996)]. Figure 6. ...
We analyze spectral attenuation of Lg waves to determine Q of the Indian shield. The dataset consists of four earthquakes recorded in the distance range of 240-2400 km. The new estimate,
Q(f) = 800f0.42 (0.1 Hz ≤ f ≤ 20 Hz), is based on a larger dataset than a previous estimate, Q(f) = 508f0.48 (1 Hz ≤ f ≤ 20 Hz). The new Q(f) of the Indian shield is comparable to the Q in regions of eastern North America where its value is relatively high, for example, the Adirondack Mountains. It is also
in agreement with previously reported Lg coda Q at f = 1 Hz for the Indian subcontinent. The revised Q(f) has important implications for the estimation of ground motions in the Indian shield region using the stochastic method
since the recorded data, presently, come mostly from large distances.
This study characterizes the impact of attenuation on source spectra for events of the 2019 Ridgecrest, California, sequence, for M ∼4–7 at distances from ∼5 to 400 km. Fourier amplitudes display a steep rate of apparent geometric spreading: R−1.6 within 60 km. Over a transition zone from ∼60 to 140 km, the apparent geometric spreading is strongly frequency dependent. This makes the robust retrieval of information on near-distance ground-motion amplitudes and source spectra intractable via traditional regressions of observations at >60 km and creates challenges for modeling the strong ground motions. Apparent source spectra and near-source observations for the Ridgecrest events are characterized by strong amplitudes despite relatively low corner frequencies. The spectral shapes are consistent on average with a Brune single-corner source model with stress ∼40 bars (4 MPa) and kappa (high-frequency site attenuation) = 0.025 for events of M 4–5.5. The largest two events are consistent in shape with the Boore, Di Alessandro, and Abrahamson (2014) double-corner model, with amplitudes being consistent with a stress of ∼40 bars for the M 6.4 event and ∼10 bars (1 MPa) for the M 7.1 event. The referenced values of stress as obtained from the corner frequency are model dependent. Comparison of the amplitude levels of the source model with observations suggests that either (1) near-distance (<10 km) finite-fault effects are strong or (2) the commonly assumed values of scaling constants in the source models are significantly biased. Fourier models of source, path, and site are difficult to connect to corresponding response spectral models due to nonuniqueness in the mapping of parameters sets between domains. Model calibration is essential in this context; it is not advisable to change single model parameters without verifying that the modified model matches direct observations, even in “plug and play” models that have separated model components.
The Jabalpur earthquake (23.08° N, 80.06° E, H = 36 km) is the first event in the Indian Peninsular shield region to be well recorded by a newly installed, 10-station, broadband seismographic network. Using these data, we estimate Q of Lg wave in the Indian shield region as Q = 508ƒ0.48 (1 ≦ ƒ ≦ 20 Hz). The corrected source spectrum, with M0 = 5.4 × 1024 dyne-cm (reported in the Harvard CMT catalog) and an ω2-source model, requires a stress parameter, Δσp, of ∼420 bar to explain high-frequency spectral level. The computed seismic energy from the records is 7.4 × 1020 erg, which yields an apparent stress and Brune stress drop of 62 and 270 bars, respectively.
The analysis of the Jabalpur earthquake provides some elements for the estimation of ground motions during future earthquakes in the Indian shield region. Based on the results of the Jabalpur earthquake and on studies of tectonically similar region of eastern North America, we assume that (1) the sources follow an ω2 model; (2) S waves dominate at R < 100 km, and Lg waves dominate at R ≧ 100 km; (3) Q(f) = 508ƒ0.48; (4) the ground motion is a bandlimited, finite-duration, Gaussian white noise; and (5) the effective duration of the ground motion equals ƒ−1c + 0.05R, where fc is the corner frequency. We apply random vibration theory (RVT) to compute various measures of ground motion, such as Amax and Vmax. At near-source distances, the source finiteness is approximately taken into account. The attenuation curves for 5.5 ≦ Mw ≦ 7 and for Δσp of 100-400 bar are presented. As expected, the predicted values (with Δσp ∼ 420 bar) agree reasonably well with the limited Jabalpur data. An Amax of ∼150 gal is predicted in the epicentral region of this earthquake. The predicted curves imply Δσp ≦ 100 bar for the Latur earthquake of 1993 (Mw = 6.1; H = 2.5 km) to explain Amax < 1 g and the reported isoseismal intensities in the epicentral region. For Koyna earthquake of 1967 (Mw 6.3), the inferred Amax and Vmax from isoseismal intensities and the recorded strong motions at the Koyna dam site are in agreement with the prediction curves for Δσp ∼ 100 bar. The RVT predictions seem reasonable but need validation from more strong-motion data, which is presently lacking.
We estimate lateral Lg wave attenuation (Q) structure at four center frequencies (0.75, 1, 2 and 2.75 Hz) along the Central California Seismic Experiment array in western US crossing the San Andreas Fault and Central Valley. We take two steps in constructing the site-response-corrected Lg Q model: (a) we compute relative site responses at each station using the reverse two-station method, and (b) we estimate Q values based on the two-station method after removing the site term. Removal of the site response in the Q model allows to probe laterally varying Q properties at mid-to-lower crustal depths. Our model follows a power-law frequency dependence as Q(f) = (81 ± 8)f^(0.62±0.11), reflecting the active tectonic setting and the presence of fluids in the region. A change in lithology from softer sediments near Pacific coast to harder basements near Sierra Nevada correlates well with the increasing trend of the Lg Q values towards east. Our laterally varying estimates at lower frequencies generally follow the variation of shear-wave velocities at deeper crustal depth and Moho temperature, whereas those at higher frequencies mostly follow the shear-wave velocity variation at shallow depth. Positive site responses obtained by reverse two-station method are found at 34 stations out of total 46 stations examined, and their responses are mostly correlated with surficial lithology (i.e., sedimentary rocks) along the profile, rather than the thickness of the sediments. The site responses also exhibit a strong negative correlation to the V_(S30) data.
Classical logarithmic linearization of the single backscattering model to estimate the coda Q (Qc) leads to biased results in the presence of low signal-to-noise ratio. Non-linear regression using the Levenberg–Marquardt (L–M) method has been proposed to estimate the Qc in the frequency range of 3–24 Hz on local earthquakes recorded in northeast region of India. Results of both classical log-linear and non-linear approaches to the single backscattering model are compared. On datasets with good signal-to-noise ratio both the approaches lead to almost the same results. However, for datasets having low signal-to-noise ratio, we found that the log-linear technique estimates are biased. Results demonstrate that the log-linear approach overestimates the Qc in comparison to the non-linear approach. Frequency dependence parameter ‘η’ for the L–M method is slightly higher than the conventional log-linear approach. The Qc variation with lapse-time is also studied with both the approaches. The biased results of log-linear approach were observed at different frequencies at all lapse times. Significantly lower Q0 (1 Hz) estimates of non-linear approach indicated more heterogeneous lithosphere than the log-linear approach. A novel approach to the single scattering model is proposed wherein nonlinear regression is performed to estimate coda Qc.Coda attenuation and its variation with lapse time is analysed (3–24 Hz) from local earthquakes of North East IndiaFor datasets having a low signal-to-noise ratio the estimates of the conventional log-linear regression were biased.Significantly lower Q0 estimates of the non-linear approach indicated a more heterogeneous lithosphere than a log-linear approach. A novel approach to the single scattering model is proposed wherein nonlinear regression is performed to estimate coda Qc. Coda attenuation and its variation with lapse time is analysed (3–24 Hz) from local earthquakes of North East India For datasets having a low signal-to-noise ratio the estimates of the conventional log-linear regression were biased. Significantly lower Q0 estimates of the non-linear approach indicated a more heterogeneous lithosphere than a log-linear approach.
The study area comprises two tectonic blocks namely, the Chotanagpur microplate and the Singhbhum microplate. Waveform data of 112 local earthquakes of magnitude MW ≥ 2.5 were considered for the present analysis. Coda Q (QC) for each event at eight different central frequencies (1–14 Hz) and four different coda windows was estimated using back-projection algorithm. The average Q0 (QC at 1 Hz) and η (exponent) values were regionalized by projecting each value in selected square grid of dimension 0.1° × 0.1°. Back-projection algorithm was used for inversion of QC, and the final values were computed after ten iterations when the residual error was reduced to acceptable level. Inversion was stabilized by a nine-point spatial smoothening Gaussian filter to compute the QC values for each frequency and subsequently, combined values of Q0 and η were also computed. The final power law equation of the coda wave attenuation for the concerned region was found to be QC = (336.38 ± 16.50)f(0.83±0.036). Q0 varies from 180 to 255, 270 to 360, 297 to 386 and 340 to 420, and η vary from 0.9 to 1.02, 0.79 to 0.89, 0.79 to 0.88, and 0.79 to 0.86 for 30, 35, 40 and 45 s coda windows. Increase in Q0 and decrease in η values with increase of coda window length shows the depth dependency of seismic wave attenuation at 1 Hz frequency. The central part, surrounding the receiver, lying at the junction of the Chotanagpur and the Singhbhum tectonic provinces, documents lower Q0 and higher η values, and presumably caused by more heterogeneities present in the area. The higher concentration of lower magnitude earthquakes in this area support this observation. The mapping values of attenuation can be utilized for hazard assessment of the area.
We investigate attenuation scattering and loss properties in Souss basin (SW of High-Atlas) as a transition zone between the High and Anti Atlas ranges. This district consists in a thinned crustal patch with shallow seismicity and loose sedimentary trenches that perform an important contribution to augment seismic attenuation. So far, no coda waves approach in our knowledge have been used to draw satisfying outputs about the attenuation properties in the region. Therefore, this update suggests to correlate the lateral changes of seismic attenuation to different characteristics and asperities i.e. seismic activity, crustal age and thickness, heat flow, and ground deformation rate. To do so, we analysed coda waves derived from waveform data of more than 23 local earthquakes from seven broadband seismometers recorded during 2010–2012 period. As a starter, we utilized the backscattering model which defines the seismic attenuation as inversely proportional to quality factor by the equation (A=1Qc). Qc estimates were deducted at various central frequency bands 1.5, 3.0, 6.0, 9.0, 12.0 and 18.0 Hz according to different lapses times. The estimated average frequency dependence quality factor gives relation Qc=120f1,01, while the average Qc values vary from 149 at 1.5 Hz to 1895 at 18 Hz central frequencies. We observed an intimate dependence between quality factor and frequency ranges, which reflects the complexity of geological/geophysical pattern in the Souss basin and the presence of a variety of heterogeneities within the underlying crust. Keywords: Attenuation, Coda waves, Quality factor, Frequency, Souss basin, Morocco
The attenuation of seismic waves is one of the basic physical parameters used in seismological studies and earthquake engineering, and is closely related to the seismicity and regional tectonic activity of a particular area. Seismic wave attenuation is caused by two major factors: scattering at heterogeneities in the earth and intrinsic absorption by anelasticity of the earth. The inverse of quality factor represents the attenuation. There are different methods for estimating the quality factor of Shear and Coda waves. In this study, the quality factors of Shear waves (Qs) and Coda waves (Qc) have been estimated in the Hormuzgan regionin the south of Iran. This region is located in the southeastern Zagros seismotectonic region. Recordings from the Bandar-Abbas (BNDS) station (located in the Hormuzgan region, 27.40º N_56.17º E) of the Iranian National Seismic Network (INSN) of local earthquakes with signal-to-noise ratios greater than 3 were used for this study. These events were recorded from June 2004 through August 2009 and registered magnitudes of between 2.5 and 5.1 (ML), epicentral distances of less than 100 km and average focal depths of about 15 km. In this study, the Coda Normalization Method (Aki, 1980) and the Single Back-Scattering Method (Aki & Chouet, 1975) are used for the estimation of Qs and Qc at the seven central frequencies of 1.5, 3.0, 4.5, 6.0, 9.0, 12.0 and 18.0 Hz. The Shear waves on 183 North-South (N-S) components and 142 East-West (E-W) components, and the Coda waves on 200 Vertical (U-D) components, have been analyzed to estimate Qs and Qc, respectively. Time windows of the Shear waves were determined by the Kinoshita algorithm and the velocity of the Shear waves was estimated at 3.5 km/s. The estimated frequency-dependent relationships of Qs on N-S and E-W components are Qs=62f^0.66 and Qs=69f^0.60, respectively. The Qc values were computed at five lapse time windows (20, 30, 40, 50 and 60 sec), starting at double the time of the primary Shear wave from the time of origin. The frequency-dependent relationships of Qc vary from Qc=61f^1.09 at 20 sec to Qc=132f^0.90 at 60 sec lapse time window. The results show an increase in Qc value with increasing lapse time windows. The estimated QC at a greater lapse time window indicates attenuation at a greater depth. In the Hormuzgan region, the values of Q at 1.0 Hz are less than 200 for the frequencydependent relationships of Qs and Qc. Therefore, the Hormuzgan region is a highly tectonically and seismically active region; also, the medium is highly heterogeneous. The results reflect sedimentary deposits and salt domes in the Hormuzgan region. The Qs frequency-dependent relationship in the Hormuzgan region is similar to that of the Ardabil and Avaj regions in northwestern Iran, and of the Strait of Messina in the south of Italy. Moreover, the QC frequency-dependent relationship in the Hormuzgan region is similar to that of the Alborz and Zagros regions in Iran and in the northwest of the Himalayan region. These regions are all tectonically and seismically active.
The propagation efficiencies of the regional phases Lg and Pn are indicative of how active and recent tectonics influence crust and uppermost mantle properties, respectively. In this study, regional scale lateral heterogeneity of Lg and Pn attenuation for the region in and around the southern Tibetan Plateau is investigated. The data set is comprised of seismograms recorded at the Chinese Digital Seismogram Network (CDSN) station LSA from regional events with epicentral distances within 11°. Attenuation of Lg and Pn is calculated using spectral methods and assuming constant QLg and QPn models for the frequency bands 0.3 to 3.0 Hz and 0.5 to 4.0 Hz, respectively. Lateral variation in attenuation is estimated by analyzing data on an event-by-event basis. Significant lateral variation is observed with QLg decreasing from about 520 for events south of LSA to about 340 for events north of LSA and QPn ∼ 670 for southern backazimuths, while QPn ∼ 240 for northern events. For Pn, this north-south variation is consistent with other observations, indicating partially melted upper mantle beneath north central Tibet. For Lg, the azimuthal variation in attenuation indicates that Lg propagation as observed at LSA is efficient for paths crossing the southern boundary of the Tibetan Plateau relative to paths within the plateau itself.
This article presents the estimation of stress drops for small to middle-sized intraplate earthquakes in the northeastern United States. The vertical-component Sg and Lg waves of 49 earthquakes were analyzed, and their seismic corner frequencies and seismic moments were determined. For these events, both short-period and broadband records were obtained from stations in the region. There are eight events each of which has an aftershock good enough to be treated as its empirical Green's function, and their corner frequencies were estimated from empirical Green's function methods. For the other events, the corner frequencies were directly estimated by the spectral fitting of the vertical component of the Sg- or Lg-wave displacement spectrum with the ω-square source spectral model, using the available broadband and high-frequency short-period data and a frequency-dependent Q correction. The static stress drops, Δσ, were then calculated from the corner frequency and seismic moment.
From our study, the source corner frequencies estimated by fitting the Lg displacement spectrum with the assumed ω-square source model are more consistent with the corner frequencies measured from empirical Green's function deconvolution method than those estimated from the intersection of horizontal low-frequency spectral asymptote and a line indicating the ω−2 decay above the corner frequency. The source corner frequencies we estimated proved to be most appropriate for the small to middle-sized earthquakes. The static stress drops calculated from these corner-frequency estimates tend to be independent of seismic moment for events above a certain size. For earthquakes with size less than about 2 × 1020 dyne-cm, the stress drop tends to decrease with decreasing moment, suggesting a breakdown in self-similarity below a threshold magnitude. A characteristic rupture size of about 100 m is implied for these smaller earthquakes.
By using the digital multi-channel microseismic monitoring system, the characteristics of blast stress wave propagation in deep complex and mined-out area and upper fractured rock mass are tested. The wave velocity is acquired by the curve fitting method, which uses the P wave triggering time and propagation distance. The results show that the wave velocities in deep complex and mined-out rock mass and upper coagula rock mass are obviously different. Fitted the curve by using the stress wave amplitude and propagation distance, it is found that the stress wave amplitude decreases in the form of power when the propagation distance increases. By using the signal spectrum analysis and filtering, the attenuation coefficient and frequency are in cubic polynomial relations, and the attenuation of the high-frequency wave is more obvious. The average quality factors in deep complex and mined-out area and upper fractured rock mass, are calculated and they are 4.055 and 2.478, far less than those of the original rock mass, indicating that the mined-out area and fracture have great influence on the stress wave propagation.
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