geosciences

Article Surface Level Synthetic Ground Motions for M7.6 2001 Earthquake

Jayaprakash Vemuri 1,*, Subramaniam Kolluru 1 and Sumer Chopra 2

1 Department of Civil Engineering, Indian Institute of Technology Hyderabad, Sangareddy, Telangana 502285, ; [email protected] 2 Institute of Seismological Research, Department of Science and Technology, , Raisan, Gandhinagar, Gujarat 382009, India; [email protected] * Correspondence: [email protected]; Tel.: +91-8886064222

 Received: 29 September 2018; Accepted: 20 November 2018; Published: 22 November 2018 

Abstract: The 2001 Gujarat earthquake was one of the most destructive intraplate earthquakes ever recorded. It had a moment magnitude of Mw 7.6 and had a maximum felt intensity of X on the Modified Mercalli Intensity scale. No strong ground motion records are available for this earthquake, barring PGA values recorded on structural response recorders at thirteen sites. In this paper, synthetic ground motions are generated at surface level using the stochastic finite- method. Available PGA data from thirteen stations are used to validate the synthetic ground motions. The validated methodology is extended to various sites in Gujarat. Response spectra of synthetic ground motions are compared with the prescribed spectra based on the seismic zonation given in the Indian seismic code of practice. Ground motion characteristics such as peak ground acceleration, peak ground velocity, frequency content, significant duration, and energy content of the ground motions are analyzed. Response spectra of ground motions for towns situated in the highest zone, seismic zone 5, exceeded the prescribed spectral acceleration of 0.9 g for the maximum considered earthquake. The response spectra for towns in seismic zone 5 exhibit peaks in the low period ranges, indicating high vulnerability of low rise structures designed as per the provisions of the Indian seismic code of practice. The response spectra for towns situated in seismic zone 3 were considerably lower than the prescribed maximum spectral acceleration of 0.4 g. The substantial damage reported in towns situated in seismic zone 3 is due to poor construction practices and non-compliance with provisions of seismic design standards.

Keywords: synthetic ground motions; stochastic finite-fault method; site effect; response spectra; peak ground acceleration

1. Introduction

The Mw 7.6 earthquake which struck Gujarat on 26 January, 2001 was the largest in India [1]. The maximum felt intensity was X on the Modified Mercalli Intensity (MMI) scale [2]. The earthquake mechanism was shallow oblique reverse faulting [1] with the epicenter about 9 km southwest of the village of Chobari in the Kutch region of Gujarat, India [3]. The earthquake caused widespread damage in the province of Gujarat. In the Kutch region, several towns were completely destroyed. Overall, it is estimated that the earthquake caused 13,819 deaths, damaged over a million structures, and the consequent economic loss was close to US$ 10 billion [4–6]. While the main fault rupture did not reach the surface, extensive secondary features, such as liquefaction in the form of sand blows/boils, craters and ground fissures were observed in the epicentral area [7] to a maximum environmental seismic intensity [8] degree of VIII. Figure1 shows the isoseismal map for the earthquake of January 26, 2001, based on damage surveys [9].

Geosciences 2018, 8, 429; doi:10.3390/geosciences8120429 www.mdpi.com/journal/geosciences Geosciences 2018, 8, x FOR PEER REVIEW 2 of 17 Geosciences 2018, 8, 429 2 of 17

44

45 46 FigureFigure 1. Isoseismal1. Isoseismal Map Map for for 2001 2001 Gujarat Gujarat Earthquake. Earthquake. The The intensity intensity is onis on the the MMI MMI scale. scale. (Inset: (Inset: Map 47 of India – Gujarat is highlighted).Map of India – Gujarat is highlighted).

48 Damage in the epicentral region of the 2001 Gujarat earthquake was not uniform and often 49 inconsistent [10]. [10]. Isoseismals Isoseismals for for the the earthquake earthquake [2] [for2] forseismic seismic zone zone 5 show 5 show that some that sometowns towns (e.g., 50 (e.g.,Bhachau, Bhachau, Rapar, Rapar, Dudhai Dudhai and andAdesar) Adesar) witnessed witnessed complete complete destruction destruction while while other other towns towns (e.g., (e.g., 51 Nakhatrana, Naliya, Khavda, and Mandvi) witnessed relatively less damage. A relationship between 52 the buildingbuilding typology typology and and ground ground motion motion characteristics characteristics can aidcan in aid understanding in understanding the unusual the unusual damage 53 patterndamage in pattern the region. in the However, region. However, ground motion ground data moti fromon this data earthquake from this is earthquake not available is andnot isavailable limited 54 andto PGA is recordingslimited to atPGA thirteen recordings stations at [11 thirteen]. The modified stations stochastic [11]. The finite-fault modified technique stochastic has finite-fault been used 55 techniqueearlier [3] tohas estimate been used ground earlier motions [3] to estimate at these grou thirteennd motions stations at and these the thirteen PGA values stations of theand syntheticthe PGA 56 valuesground of motions the synthetic were validatedground motions with recorded were validated PGAs from with 13recorded stations PGAs (marked from in 13 boxes stations in Figure(marked1). 57 inHowever, boxes in the Fig.1). ground However, motions the were ground generated motions at rock were surface, generated and may at rock not be surface, representative and may of not the 58 representativeactual motions of experienced the actual atmotions the surface experienced level, which at the may surface be obtained level, which only after may accounting be obtained for only soil 59 afteramplification. accounting Only for soil surface amplification. level ground Only motions surface can level help ground to understand motions can the help actual to damageunderstand pattern the 60 actualobserved damage in the pattern earthquake. observed in the earthquake. 61 In this paper, ground motions are estimated using the modified stochastic stochastic finite-fault finite-fault method, method, 62 at surface surface level level for for various various sites sites which which experien experiencedced damage damage in the in the2001 2001 Gujarat Gujarat earthquake. earthquake. The 63 Thevalidation validation study study performed performed at 13 stations at 13 stations where where actual actual PGA values PGA values are available are available constrains constrains the source the 64 andsource dispersion and dispersion parameters parameters used usedin the in method. the method. Essential Essential characteristics characteristics of ofthese these synthetic synthetic ground ground 65 motions are correlated withwith isoseismalsisoseismals andand reconnaissancereconnaissance reports reports of of the the 2001 2001 Gujarat Gujarat earthquake. earthquake. 1.1. Seismotectonics of Gujarat 66 Seismotectonics of Gujarat Physio-graphically, the Gujarat region comprises three distinct zones: Kutch, Saurashtra and 67 Physio-graphically, the Gujarat region comprises three distinct zones: Kutch, Saurashtra and Mainland Gujarat. The Gujarat region is a junction of three tectonic : Kutch, Cambay and Narmada 68 Mainland Gujarat. The Gujarat region is a junction of three tectonic rifts: Kutch, Cambay and with many active faults [12–14]. These rifts were formed by rifting along major Precambrian trends. 69 Narmada with many active faults [12,13,14]. These rifts were formed by rifting along major The rifting occurred at successive stages during the northward movement of the after 70 Precambrian trends. The rifting occurred at successive stages during the northward movement of the the breakup from Gondwanaland in the Late Triassic or Early Jurassic. The rifting developed around 71 Indian plate after the breakup from Gondwanaland in the Late Triassic or Early Jurassic. The rifting the Saurashtra horst. The Kutch rifting took place in the Late Triassic–Early Jurassic, Cambay rifting 72 developed around the Saurashtra horst. The Kutch rifting took place in the Late Triassic–Early 73 Jurassic, Cambay rifting in Early Cretaceous, and Narmada rifting in the Late Cretaceous [12]. The

Geosciences 2018, 8, x FOR PEER REVIEW 3 of 17

shear zone during the post-collision compressive regime of the Indian plate, with strike-slip movements along subparallel faults. The Kutch mainland fault along the rift axis became the active principal fault. The eastern part of this fault, where it overhangs the South Wagad fault, is the most strained region [13]. The epicenter of the 2001 Gujarat earthquake and its aftershocks are located in the Kutch region. The overall earthquake hazard in Gujarat ranges from low to high, and based on the estimated hazard level, the seismic zoning map of India [15] has assigned four seismic zones to Gujarat (Figure 2a), ranging from Zone II (low) to Zone V (high). As the Kutch region has the highest earthquake hazard it lies in the Zone V, with a pseudo-spectral acceleration (PSA) at Maximum Considered Earthquake (MCE) level of 0.9 g and can expect earthquake damage corresponding to Modified Mercalli Intensity (MMI) level of IX or more. A belt of 60 km–70 km width around this zone, which Geosciences 2018, 8, 429 3 of 17 covers areas of northern part of Saurashtra and areas along the eastern borders of Kutch, lies in Zone IV (PSA at MCE level is 0.625 g) of the seismic zoning map. Earthquakes arising in Kutch and local inearthquakes Early Cretaceous, along North and Narmada Kathiawar rifting fault in thenorthern Late Cretaceous Saurashtra [can12]. le Thead to rifting intensity ceased (MMI) in the of Late VIII Cretaceousin this Zone. era Due during to moderate the pre-collision local earthquakes stage of the Indianor strong plate. Kutch The earthquakes, Kutch rift basin Mainland became aGujarat shear zonewhich during lies in theZone post-collision III (PSA at MCE compressive level is 0.4 regime g) can of expect the Indian intensity plate, (MMI) with level strike-slip of VII. movements alongAmong subparallel the three rift faults. zones, The presently Kutch mainlandthe Kutch faultregion along is seismically the rift axis most became active. the The active Kutch principal region fault.of Gujarat The easternis one of part the of most this earthquake fault, where prone it overhangs intra-continental the South regions Wagad in fault, the isworld the mostand the strained mean regionreturn period [13]. The of earthquakes epicenter of in the the 2001Kutch Gujarat region ha earthquakes been estimated and its to aftershocks be 13.34 years are [16]. located This inregion the Kutchhas witnessed region. major intraplate earthquakes in the past [7,17]. Some major earthquakes which have struckThe the overall Kutch earthquake region are hazard the 1668 in Gujarat Indus delta ranges earthquake, from low to 1819 high, Kutch and based earthquake, on the estimatedand 1845 hazardLakhpat level, earthquakes. the seismic Several zoning moderate map of India earthquakes [15] has assigned (5 < M < four6) have seismic also zonesoccurred to Gujarat in the region, (Figure 2e.g.,a), ranging1956 Anjar from earthquake Zone II (low) (M to 6.0). Zone Figure V (high). 2b shows As the some Kutch of region the major has thefaults highest in the earthquake Kutch region, hazard the itKutch lies in Mainland the Zone fault V, with (KMF), a pseudo-spectral Katrol Hill Fault acceleration (KHF), Allah (PSA) Bund at Maximum Fault (ABF), Considered Island Belt Earthquake Fault (IBF), (MCE)Gedi Fault level (GF) of 0.9 and g and the canNorth expect Kathiawar earthquake Fault damage (NKF). correspondingThe epicenter of to the Modified 2001 Gujarat Mercalli earthquake Intensity (MMI)is also levelmarked of IXin orFigure more. 2b. A It beltmay of be 60 observed km–70 km that width the key around faults this in the zone, Kutch which region covers trend areas in the of northerneast-west part direction. of Saurashtra The epicentral and areas region along of the the eastern 2001 earthquake borders of Kutch,lies at a lies distance in Zone of IV400km (PSA from at MCE the levelIndian-Eurasian is 0.625 g) of plate the seismic boundary. zoning It is map. known Earthquakes that both arisingthe India–Eurasian in Kutch and plate local earthquakescollision processes along Northand the Kathiawar dilatational fault perturbations in northern Saurashtra in the ambient can lead strain to intensityfield due (MMI) to past of earthquakes VIII in this Zone.in the Due Kutch to moderateregion have local loaded earthquakes contiguous or strongregions Kutch which earthquakes, contributed to Mainland the 2001 Gujarat earthquake which lies in[18]. Zone These III (PSAobservations at MCE levelindicate is 0.4 the g) high can expectseismic intensity hazard potential (MMI) level for the of VII. Kutch region.

(a) (b)

FigureFigure 2. 2.( a(a)) Seismic Seismic Zones Zones in in Gujarat Gujarat [ 15[15]]—the - the KutchKutch regionregion isis highlighted;highlighted; ((bb)) MapMap showingshowing majormajor faultsfaults in in the the Kutch Kutch region region (Zone (Zone V). V). The The epicenter epicenter of of the the 2001 2001 Gujarat Gujarat earthquake earthquake is is shown shown as as a a star. star.

1.2. MethodologyAmong the threefor Generation zones, presently of Synthetic the Accelerograms Kutch region is seismically most active. The Kutch region of Gujarat is one of the most earthquake prone intra-continental regions in the world and the mean return period of earthquakes in the Kutch region has been estimated to be 13.34 years [16]. This region has witnessed major intraplate earthquakes in the past [7,17]. Some major earthquakes which have struck the Kutch region are the 1668 Indus delta earthquake, 1819 Kutch earthquake, and 1845 Lakhpat earthquakes. Several moderate earthquakes (5 < M < 6) have also occurred in the region, e.g., 1956 Anjar earthquake (Mw 6.0). Figure2b shows some of the major faults in the Kutch region, the Kutch Mainland fault (KMF), Katrol Hill Fault (KHF), Allah Bund Fault (ABF), Island Belt Fault (IBF), Gedi Fault (GF) and the North Kathiawar Fault (NKF). The epicenter of the 2001 Gujarat earthquake is also marked in Figure2b. It may be observed that the key faults in the Kutch region trend in the east-west direction. The epicentral region of the 2001 earthquake lies at a distance of 400km from the Indian-Eurasian plate boundary. It is known that both the India–Eurasian plate collision processes and the dilatational Geosciences 2018, 8, 429 4 of 17 perturbations in the ambient strain field due to past earthquakes in the Kutch region have loaded contiguous regions which contributed to the 2001 Gujarat earthquake [18]. These observations indicate the high seismic hazard potential for the Kutch region.

1.2. Methodology for Generation of Synthetic Accelerograms Strong motion records from major earthquakes in Gujarat are not available. In such regions where a historical database of strong ground motions is unavailable, modified records may be obtained by either generation of synthetic records or by scaling natural records obtained from other regions. In this study, the modified stochastic finite fault method [19] is used to generate synthetic ground motions. Subsequently, the synthetic ground motions are used to derive response spectra. The procedure to obtain synthetic ground motions using the modified stochastic method [19] is now described. In the stochastic point source model [20] acceleration spectrum, A( f ) of shear waves at a distance, R from a seismic source with the moment, Mo may be estimated as

 2 Rθϕ·FS·PR (2π f ) −π f R A( f ) = · Mo · · exp(−πκ f ) · exp( )·GS(R), (1) 4·π·ρ·β3  f 2 Qβ 1 + fc where f is the frequency, Rθϕ is the radiation pattern, FS is amplification due to the free surface, PR is the reduction factor that accounts for the partitioning of energy into two horizontal components, ρ is the density, β is the shear wave velocity, fc is the corner frequency, Q is the quality factor, GS(R) is the geometrical spreading term, and κ is spectral decay parameter called kappa [21]. The stochastic point source model was extended [22] to large seismic sources by dividing entire fault into smaller sub-faults and considering each sub-fault as a point source. The contributions from all sub-faults are summed after accounting for the time delay to obtain the ground motion acceleration, a(t) from the entire fault,

( ) = nl nw +  a t ∑i=1 ∑j=1 aij t ∆tij , (2) where aij (t) are the contribution from each sub-fault, nl and nw (N = nl × nw) are the number of sub-faults along the length and width of the entire fault and ∆tij is the relative delay time for the wave from ijth sub-fault to reach the point under observation. The stochastic finite-fault method was improved [19] to introduce the concept of dynamic corner frequency. The corner frequency is a function of time, and during the fault rupture process, the corner frequency depends on the cumulative ruptured area. The rupture history of the fault controls the frequency content of the simulated time th series of each sub-fault. The dynamic corner frequency of the ij sub-fault, fcij, is defined as [19]:

− 1 6 1 fcij(t) = NR(t) 3 4.9 × 10 β (∆σ/Mo−ave) 3 , (3) where NR(t) is the cumulative number of ruptured sub-faults at time t, ∆σ is the stress drop and Mo−ave is the average seismic moment of sub-faults (= Moe/N). At the time the rupture ends, tend, − 1 − 1 the entire fault is ruptured, i.e. NR(t) 3 = N(t) 3 , and thus, the corner frequency of the complete fault is described as − 1 6 1 fcij(tend) = N 3 4.9 × 10 β (∆σ N/Mo) 3 , (4) To conserve the total radiated energy from sub-faults at high frequencies and to balance the level of the spectrum of the sub-faults, a scaling factor, Hij, was defined as [19]:

 2 21/2 n 2 h 2io n 2 h 2io Hij = N ∑ f / 1 + ( f / fc) / ∑ f / 1 + f / fcij , (5) Geosciences 2018, 8, x FOR PEER REVIEW 5 of 17

Geosciencesthe intensity2018, 8observations, 429 and the structural response recorder observations [3]. The duration model5 of 17 for eastern North America [30] was adopted since the predicted ground motions for the 2001 Gujarat earthquake seem close to ground motions from earthquakes in central or eastern North America To generate ground motions for the 2001 Gujarat earthquake, EXSIM software, which is based on (e.g.[3,31]). Based on inversion of teleseismic waves, the fault dimensions have been estimated [32] stochastic finite-fault method [19] is used. Details of the source characteristics and damage pattern of as 75 km × 35 km. The parameters and the slip distribution data for the ruptured fault of the 2001 the earthquake are available in literature [18,23–28]. The 2001 Gujarat earthquake (Mw 7.6) being an earthquake were obtained from the study [32]. Figure 3 shows the slip distribution as estimated [32]. intraplate earthquake, has been estimated as a high-stress drop event. The aftershock analysis of the Slip is estimated in meters. The geometric spreading parameters and the frequency dependent earthquake implied a high-stress drop of 126–246 bars of the main event [23]. A stress drop of 200 bars attenuation relation developed for the region [31] was used in the model. was suggested [25] on the basis of stochastic finite-fault modelling of the earthquake. A stress drop Table 1 shows the model parameters used in the modified stochastic finite fault method for of 150–200 bars has been suggested [29] using stochastic point source modelling of the earthquake. generation of ground motions at bedrock level. The coordinates of the earthquake are as reported by As stress drop is a calibration factor in EXSIM, in this study, the simulations were tried for stress USGS [33]. The model also includes the pulsing area, to account for the slip behavior of earthquake drops of 100, 125, 150 and 160 bars. PGA values obtained with 125 bars were closest to actual PGA ruptures where the slip may occur only on the part of the fault at any particular time [19]. PGA data values, and the stress drop of 125 bars was used for simulations. The stress drop value satisfies the in the 2001 Gujarat earthquake was recorded at a variety of soil conditions. The PGA data was intensity observations and the structural response recorder observations [3]. The duration model for corrected [11] to a common geological site condition. The National Earthquakes Hazard Reduction eastern North America [30] was adopted since the predicted ground motions for the 2001 Gujarat Program (NEHRP), B/C boundary (Shear Wave Velocity, 𝑉 = 760 m/s) of U.S. national seismic earthquake seem close to ground motions from earthquakes in central or eastern North America hazard maps [34], were chosen to represent the common site condition. The correction factors, to 𝑉 (e.g., [3,31]). Based on inversion of teleseismic waves, the fault dimensions have been estimated [32] = 760 m/s site condition, were determined using factors from reference [35]. The surface geology at as 75 km × 35 km. The parameters and the slip distribution data for the ruptured fault of the 2001 each recording site was determined at a scale of 1: 2,000,000 [36] using the classification scheme of earthquake were obtained from the study [32]. Figure3 shows the slip distribution as estimated [ 32]. Quaternary sediments (Q) as NEHRP C, and rock (R). Slip is estimated in meters. The geometric spreading parameters and the frequency dependent attenuation relation developed for the region [31] was used in the model.

20 Slip 15 (metres) 6-8 10 4-6 5 2-4 0

0-2 -5 Depth (kilometres) -10 -55 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 Strike (kilometres)

Figure 3. The slip distribution on the fault plane used in the present study [32]. The hypocenter of the Figure 3. The slip distribution on the fault plane used in the present study [32]. The hypocenter of the 2001 Gujarat earthquake is shown as a star on the fault plane. 2001 Gujarat earthquake is shown as a star on the fault plane. Table1 shows the model parameters used in the modified stochastic finite fault method for generation of groundTable 1 Model motions Parameters at bedrock for 2001 level. Gujarat The coordinates earthquake used of the in earthquake the present study. are as reported by

USGS [33]. The modelMagnitude, also includes 𝑀 the pulsing area, to account7.6 for the slip behavior of earthquake [33] ruptures where theLatitude, slip may longitude occur only on the part of the23.42 fault atN, any 70.23 particular E time [19].[33] PGA data in the 2001 GujaratHypocente earthquaker depth was recorded at a variety of 16 soil km conditions. The PGA[33] data was corrected [11] to aFault common strike, geological dip site condition. The National78 , 58 Earthquakes Hazard[32] Reduction Fault length, width 75 km, 35 km [32] Program (NEHRP), B/C boundary (Shear Wave Velocity, V = 760 m/s) of U.S. national seismic hazard Slip distribution s [32] maps [34], wereDepth chosen of totop represent of rupture the common site condition. The 10 k correctionm factors, to Vs[28]= 760 m/s site condition,No. were of faults determined along strike, using dip factors from reference [35]. 15, The 7 surface geology at each [32] recording site wasH determinedypocenter location at a scaleon theof fault 1: plane 2,000,000 [36] using the classification 11, 5 scheme of Quaternary [32] sediments (Q) asShear NEHRP wave C, velocit and rocky (R). 3.7 km/s Hard Rock Density 2.8 gm/cm3 Hard Rock Stress drop 100, 125, 150 and 160 bars [3] Inelastic attenuation Q(f) 790𝑓. [29] 1𝑅⁄ (𝑅 40𝑘𝑚) Geometric spreading 1𝑅⁄ . (40𝑘𝑚 𝑅 80𝑘𝑚) [29] 1𝑅⁄ . (𝑅 80𝑘𝑚)

Geosciences 2018, 8, 429 6 of 17

Table 1. Model Parameters for 2001 Gujarat earthquake used in the present study.

Magnitude, Mw 7.6 [33] Latitude, longitude 23.42◦ N, 70.23◦ E[33] Hypocenter depth 16 km [33] Fault strike, dip 78◦, 58◦ [32] Fault length, width 75 km, 35 km [32] Slip distribution [32] Depth of top of rupture 10 km [28] No. of faults along strike, dip 15, 7 [32] Hypocenter location on the fault plane 11, 5 [32] Shear wave velocity 3.7 km/s Hard Rock Density 2.8 gm/cm3 Hard Rock Stress drop 100, 125, 150 and 160 bars [3] Inelastic attenuation Q(f) 790 f 0.35 [29] 1/R (R < 40 km) Geometric spreading 1/R0.5 (40 km < R < 80 km) [29] 1/R0.55 (R > 80 km) rmin = 10 km, rd1 = 40 km, rd2 = 80 km, Duration properties durmin = 1 s, [30] b1 = 0.16, b2 = −0.03, b3 = 0.04 Pulsing percent 50% [19] Crustal amplification Hard Rock [37] Crustal amplification B/C boundary [38]

Table2 shows the PGA values of the synthetic accelerograms and the corrected values [ 11] for B/C boundary condition. The simulations were conducted at hard rock sites with a shear wave velocity of 2900 m/s. The simulations were also carried out at generic rock using crustal amplification factors estimated for eastern North America [38] at the NEHRP B/C boundary (Vs = 760 m/s). The values at Anjar, Naliya, Junagarh, , and Anand are comparable at the NEHRP B/C conditions (Vs 760m/s). The corresponding residuals at these sites are 0.016, 0.007, −0.009, 0 and −0.012, respectively. The values at Khambaliya, Jamjodhpur, and Amreli compare well with PGAs estimated at these sites for hard rock conditions. The corresponding residuals at these sites are −0.032, 0.015, and −0.006, respectively. These sites are hard rock sites situated on Deccan basalt. The values at Kandla, Niruna, Dwarka, Porbandar and Cambay are different than estimated from simulated ground motions, perhaps because correction factors [11] are not suited for quaternary sites in Gujarat. The corresponding residuals at these sites are −0.120, −0.119, −0.138, −0.89 and 0.081, respectively. Figure4 shows the simulated ground motions at some sites at the bedrock level.

Table 2. Comparison of PGA values – Present Study and Recorded [11].

Recorded PGA (g) of PGA (g) of Site Epicentral PGA (g) Simulated Simulated Recorded S. No. Site Class Distance V = 760 m/s GM GM Residuals PGA (g) s (NEHRP) (km) (Corrected to Vs = 760 m/s Vs = 2900 m/s B/C) B/C (NEHRP) (Hard Rock) 1 Anjar C 44 0.65 0.580 0.564 0.315 0.016 2 Kandla C 53 0.35 0.326 0.446 0.241 −0.120 3 Niruna D 97 0.32 0.241 0.360 0.208 −0.119 4 Naliya C 147 0.29 0.215 0.222 0.123 0.007 5 Khambaliya A 150 0.072 0.143 0.192 0.104 −0.032 6 Jamjodhpur A 166 0.088 0.088 0.128 0.073 0.015 7 Dwarka D 188 0.085 0.061 0.199 0.107 −0.138 8 Porbandar D 206 0.076 0.054 0.143 0.076 −0.089 9 Junagarh A 216 0.075 0.075 0.084 0.049 −0.009 10 Amreli A 225 0.039 0.039 0.080 0.045 −0.006 Geosciences 2018, 8, x FOR PEER REVIEW 6 of 17

𝑟 = 10 𝑘𝑚, 𝑟 =40 𝑘𝑚, 𝑟 =80 𝑘𝑚, Duration properties 𝑑𝑢𝑟𝑚𝑖𝑛 =1𝑠, [30] 𝑏 =0.16, 𝑏 = −0.03, 𝑏 =0.04 Pulsing percent 50% [19] Crustal amplification Hard Rock [37] Crustal amplification B/C boundary [38]

Table 2 shows the PGA values of the synthetic accelerograms and the corrected values [11] for B/C boundary condition. The simulations were conducted at hard rock sites with a shear wave velocity of 2900 m/s. The simulations were also carried out at generic rock using crustal amplification

factors estimated for eastern North America [38] at the NEHRP B/C boundary (𝑉 = 760 m/s). The values at Anjar, Naliya, Junagarh, Ahmedabad, and Anand are comparable at the NEHRP B/C conditions (Vs 760m/s). The corresponding residuals at these sites are 0.016, -0.119, -0.009, 0 and -0.012, respectively. The values at Khambaliya, Jamjodhpur, and Amreli compare well with PGAs estimated at these sites for hard rock conditions. The corresponding residuals at these sites are 0.039, 0.015, and -0.006, respectively. These sites are hard rock sites situated on Deccan basalt. The values at Kandla, Niruna, Dwarka, Porbandar and Cambay are lower than estimated from simulated ground motions, perhaps because correction factors [11] are not suited for quaternary sites in Gujarat. The corresponding residuals at these sites are 0.120, 0.033, -0.138, -0.89 and 0.081, respectively. Figure 4 shows the simulated ground motions at some sites at the bedrock level.

Table 2 Comparison of PGA values – Present Study and Recorded [11].

PGA (g) of PGA(g) of Recorded PGA Simulated Simulated Site Epicentral (g) S. Recorded GM GM Site Class Distance Vs 760 m/s Residuals No. PGA (g) Vs 760 m/s Vs 2900m/s (NEHRP) (km) (Corrected to B/C (Hard Geosciences 2018, 8, 429 B/C) 7 of 17 (NEHRP) Rock) 1 Anjar C 44 0.65 0.580 0.564 0.315 0.016 2 Kandla C 53 0.35 0.326 0.446 0.241 0.120 3 Niruna D 97 Table 0.32 2. Cont. 0.241 0.360 0.208 0.033 4 Naliya C 147 0.29 0.215 0.222 0.123 -0.119 5 Khambaliya A 150 0.072 Recorded 0.143 PGA 0.192 (g) of PGA 0.104 (g) of 0.039 Site Epicentral PGA (g) Simulated Simulated 6 Jamjodhpur A 166 Recorded 0.088 0.088 0.128 0.073 0.015 S. No. Site Class Distance V = 760 m/s GM GM Residuals 7 Dwarka D 188 PGA 0.085 (g) s 0.061 0.199 0.107 -0.138 (NEHRP) (km) (Corrected to V = 760 m/s V = 2900 m/s 8 Porbandar D 206 0.076 0.054 s 0.143 s 0.076 -0.089 B/C) B/C (NEHRP) (Hard Rock) 9 Junagarh A 216 0.075 0.075 0.084 0.049 -0.009 1110 AhmedabadAmreli D A 238 225 0.11 0.039 0.080 0.039 0.080 0.080 0.045 0.046 -0.006 0 1211 Ahmedabad Cambay D D 266 238 0.20 0.11 0.143 0.080 0.062 0.080 0.046 0.038 0 0.081 13 Anand D 288 0.058 0.041 0.053 0.032 −0.012 12 Cambay D 266 0.20 0.143 0.062 0.038 0.081 13 Anand D 288 0.058 0.041 0.053 0.032 -0.012 0.4 0.2 Time (s) 0 0 2 4 6 8 101214161820 PGA (g) PGA -0.2 -0.4 Anjar 0.4 0.2 Time(s) 0 0 5 10 15 20 25 30 35 PGA (g) PGA -0.2 Geosciences 2018, 8, x FOR PEER REVIEW Kandla7 of 17 -0.4 0.20

0.10 Time (s) 0.00 0 2 4 6 8 10 12 14 16 18 20 PGA (g) PGA -0.10 -0.20 Niruna 0.20 0.10 Time (s) 0.00 0 2 4 6 8 10 12 14 16 18 20 PGA (g) PGA -0.10 -0.20 Naliya 0.10 0.05 Time (s) 0.00 0 5 10 15 20 25 30 PGA (g) PGA -0.05 -0.10 Khambaliya 0.10 0.05 Time (s) 0.00 0 2 4 6 8 10 12 14 16 18 20 PGA (g) PGA -0.05 -0.10 Dwarka 0.02 0.01 Time (s) 0.00 -0.01 0 5 10 15 20 25 30 35 40 PGA (g) PGA -0.02 Amreli

0.1 0.05 Time (s) 0 0 5 10 15 20 25 30 35 40 45 50 55 PGA (g) PGA -0.05 Ahmedabad -0.1

FigureFigure 4. 4.Synthetic Synthetic Ground Ground Motions at at Rock Rock Level. Level.

Results from Table 2 indicate a reasonable match between recorded PGAs and PGAs of synthetic ground motions. The validated methodology is extended to obtain synthetic ground motions at various sites across Gujarat. After validation of PGAs at rock level, surface level strong ground motions are obtained by incorporating local site effects in the EXSIM code. The site amplification functions have been estimated by reference [39] using the horizontal-to-vertical spectral ratio (HVSR) technique by observing local earthquake data. Figure 5 shows plots of soil amplification functions at some sites in Gujarat. Ground motions are amplified significantly at various frequency levels. Soil amplification functions corresponding to each particular site are used to generate ground motions using EXSIM at bedrock level and amplified to surface level.

Geosciences 2018, 8, 429 8 of 17

Results from Table2 indicate a reasonable match between recorded PGAs and PGAs of synthetic ground motions. The validated methodology is extended to obtain synthetic ground motions at various sites across Gujarat. After validation of PGAs at rock level, surface level strong ground motions are obtained by incorporating local site effects in the EXSIM code. The site amplification functions have been estimated by reference [39] using the horizontal-to-vertical spectral ratio (HVSR) technique by observing local earthquake data. Figure5 shows plots of soil amplification functions at some sites in Gujarat. Ground motions are amplified significantly at various frequency levels. Soil amplification functions corresponding to each particular site are used to generate ground motions using EXSIM at bedrockGeosciences level 2018 and, 8, x FOR amplified PEER REVIEW to surface level. 8 of 17

Adesar Bhachau Dhori Dudhai 7 Khavda Mandvi Nakhtarana Morbi 6

5

4

3 Spectral Ratio 2

1

0 0246810 Frequency (Hz) FigureFigure 5. 5.Site Site amplification amplification plots plots for for various various sites. sites. 2. Results: Surface Level Ground Motions and Response Spectra 2. Results: Surface Level Ground Motions and Response Spectra The modified stochastic finite-fault method is used to derive synthetic ground motions at surface The modified stochastic finite-fault method is used to derive synthetic ground motions at surface level for various towns (where site amplification functions were available) across various seismic zones level for various towns (where site amplification functions were available) across various seismic V, IV and III [15]. Table3 shows the list of towns and characteristics of the synthetic ground motions zones V, IV and III [15]. Table 3 shows the list of towns and characteristics of the synthetic ground generated for these towns. Due to the variations of Gauss white noise (series of random pulses) used motions generated for these towns. Due to the variations of Gauss white noise (series of random in the EXSIM method, the synthetic ground motion is different for each realization, and hence the pulses) used in the EXSIM method, the synthetic ground motion is different for each realization, and presented results are the average of ten realizations. The varied local soil conditions are accounted hence the presented results are the average of ten realizations. The varied local soil conditions are using crustal and soil amplification factors. Parameters for the model were obtained in the previous accounted using crustal and soil amplification factors. Parameters for the model were obtained in the section by validating PGA at 13 sites. From the synthetic accelergrams, ground motion characteristics previous section by validating PGA at 13 sites. From the synthetic accelerograms, ground motion such as, peak ground acceleration, predominant period, Fourier and response spectra are obtained. characteristics such as, peak ground acceleration, predominant period, Fourier and response spectra Table3 includes the name of the recording station, site classification and epicentral distance of are obtained. the station. Site classification for strong motion stations in Gujarat has been performed [40] using the Table 3 includes the name of the recording station, site classification and epicentral distance of fundamental period from average horizontal-to-vertical response spectral ratios. Sites were classified the station. Site classification for strong motion stations in Gujarat has been performed [40] using the into seven classes based on the fundamental period, as per the scheme proposed by [41]. Class I, II, III, fundamental period from average horizontal-to-vertical response spectral ratios. Sites were classified and IV correspond to ground motions having fundamental periods in the range of 0–0.2 s, 0.2–0.4 s, into seven classes based on the fundamental period, as per the scheme proposed by [41]. Class I, II, 0.4–0.6III, and s andIV correspond above 0.6 s, to respectively. ground motions Class having V, VI and fundamental VII correspond periods to sitesin the with range non-unique of 0–0.2 s, peaks0.2–0.4 A V ins, H/V. 0.4–0.6 The s peakand above ground 0.6 acceleration s, respectively. (PGA), Class peak V, ground VI and velocity VII correspond (PGV), and to the sites peak with ground non-unique/ ratiopeaks for in ground H/V. motionsThe peak are ground also tabulated. acceleration The significant (PGA), peak duration ground is the velocity interval (PGV), of time and over the which peak aground proportion 𝐴/𝑉 (percentage) ratio for ground of the motions total Arias are Intensity also tabulated. is accumulated The significant (default duration is the interval is the interval between of thetime 5% over and 95%which thresholds). a proportion The (percentage) frequency content of the to intal the Arias ground Intensity motion is isaccumulated represented (default using single is the T T parameterinterval between estimates the such 5% as, and predominant 95% thresholds). period, Thep and frequency mean period, contentm. Thein the predominant ground motion period is is the period at which the maximum spectral acceleration occurs in an acceleration response spectrum represented using single parameter estimates such as, predominant period, 𝑇 and mean period, calculated at 5% damping. The mean period, Tm represents the average frequency content and is 𝑇. The predominant period is the period at which the maximum spectral acceleration occurs in an acceleration response spectrum calculated at 5% damping. The mean period, 𝑇 represents the average frequency content and is estimated by equation [6] where 𝐶 are the Fourier amplitudes, and 𝑓 represent the discrete Fourier transform frequencies between 0.25 and 20 Hz [42]. 𝑇 =𝛴 𝛴𝐶 , (6)

Table 3 Average Characteristics of Synthetic Ground Motions (Surface Level).

S. Distance PGA PGV AI 𝑻 𝑻 Duration Station Site Class 𝒑 𝒎 No. (km) (g) (m/s) (m/s) (s) (s) (s) 1 Dudhai III 15 0.74 0.87 7.58 0.21 0.55 12.81 2 Bhachau III 19 0.64 0.54 6.14 0.10 0.31 18.08 3 Suvai II 34 0.38 0.32 2.11 0.22 0.35 21.38

Geosciences 2018, 8, 429 9 of 17

estimated by equation [6] where Ci are the Fourier amplitudes, and fi represent the discrete Fourier transform frequencies between 0.25 and 20 Hz [42].

2 ! Ci 2 Tm = Σ /ΣCi , (6) fi

Table 3. Average Characteristics of Synthetic Ground Motions (Surface Level).

Distance PGA PGV AI Duration S. No. Station Site Class T (s) T (s) (km) (g) (m/s) (m/s) p m (s) 1 Dudhai III 15 0.74 0.87 7.58 0.21 0.55 12.81 2 Bhachau III 19 0.64 0.54 6.14 0.10 0.31 18.08 3 Suvai II 34 0.38 0.32 2.11 0.22 0.35 21.38 4 Lakadia V 36 0.42 0.53 3.20 0.18 0.50 21.73 5 Rapar I 46 0.33 0.18 2.29 0.11 0.19 22.80 6 Dhori III 49 0.74 0.63 5.02 0.26 0.40 5.92 7 Khavda II 73 0.35 0.18 1.97 0.15 0.23 12.24 8 Bela II 77 0.12 0.12 0.36 0.19 0.41 21.39 9 Adesar II 78 0.15 0.13 0.47 0.19 0.38 22.88 10 Mandvi VII 111 0.24 0.17 0.76 0.14 0.26 9.26 11 Dayapur I 141 0.13 0.09 0.18 0.16 0.29 7.80 12 Nakhatrana V 155 0.20 0.16 0.38 0.13 0.33 8.31 13 Naliya VI 192 0.14 0.11 0.16 0.13 0.39 8.07 14 Morbi I 93 0.16 0.12 0.57 0.17 0.25 21.13 15 Dwarka VI 183 0.03 0.03 0.01 0.25 0.46 9.95

Overall, from Table3, it is observed that PGA and PGV of generated earthquake ground motions decrease with increasing distance from the epicenter. There are some exceptions to this trend, due to directivity and liquefaction effects. The Dhori village, which is situated close to the western edge of the fault, experienced higher PGA (0.74 g) and PGV level (0.63 m/s) due to the effect of western directivity. Previous research [43] has also reported western directivity of the fault rupture and seismic energy propagation in the 2001 Gujarat earthquake. The significant duration of the seismic motion is only 6 s, and the Arias Intensity is very high (5.02 m/s). These observations indicate a high concentration of seismic energy. Further, from Table3, we also observe that Mandvi, a coastal town situated at 111 km from the epicenter, experienced high PGA, possibly due to soil amplification. The port town of Kandla also observed higher damage due to liquefaction [9], as compared to other towns situated at similar distances. Another general observation from Table3: the estimates of frequency content, such as predominant period, indicate that the frequency level of ground motions is close to fundamental frequency levels of low rise 1–2 story structures. The mean period estimates reveal that the average frequency content in ground motions are closer to fundamental frequency levels of 3–4 story structures. Figures6–9 show plots of the pseudo-spectral acceleration (PSA) at 5% damping for various sites situated in Zone 5. In these figures, the prescribed design response spectra for Zone 5, corresponding to the Maximum Considered Earthquake (MCE) and Design Basis Earthquake (DBE) from the Indian code of design practice [15], which forms the basis of seismic design of structures in India is also shown for comparison, in bold and dashed lines, respectively. The mean of the response spectra derived from ten synthetic ground motions is also shown. The MCE and DBE represent the 2% and the 10% probabilities, respectively of being exceeded in 50 years. Figure6 shows response spectra for two towns, Dudhai and Bhachau located at epicentral distances of 15 km and 19 km, respectively. The two towns lie in Seismic Zone 5 of the Indian code where the code prescribes a maximum spectral acceleration of 0.9 g. At these small epicentral distances, the response spectra exceed both the MCE and DBE level response spectra. The mean response spectra for Dudhai (Figure6a) exceeds the MCE level. The mean response spectra for Bhachau (Figure6b) exceeds the MCE level till a period of 1 s and lie around the MCE level in the period range of 1–4 s. In both towns, even structures designed as per the seismic provisions of the code would not have survived the extreme level of seismic forces imposed on them. The response spectra also exhibit sharp peaks in the low period region indicating destruction of low rise structures. Geosciences 2018, 8, 429 10 of 17

The predominant period for the synthetic ground motions at Dudhai and Bhachau is 0.21 s and 0.1 s, respectively, indicating the presence of high-frequency content, due to the 2001 Gujarat earthquake. For these two towns, the predominant frequencies were reported [39] as 10 Hz and 8.9 Hz, respectively. The predominant form of construction in these towns consisted of low rise unreinforced masonry and reinforced concrete structures, which are susceptible to high-frequency ground motions. In both towns, most (> 75%) buildings constructed with infield-stone, clay and unburnt-brick witnessed total damage [2]. In both towns, many (> 50%) ordinary brick structures, buildings of the large block and prefabricated type, half-timbered structures witnessed total damage. In both towns, many (> 50%) reinforced buildings and well-built wooden structures were destroyed [2]. In the town of Bhachau, even well-built reinforced concrete structures were totally devastated. The observations for both towns are consistent with the response spectra derived from synthetic ground motions. Both towns were assignedGeosciences an2018 MMI, 8, x FOR intensity PEER REVIEW level X [2]. 10 of 17

3 2.5 MCE MCE 2.5 2 DBE DBE 2 Mean Spectra Mean Spectra 1.5

1.5 PSA (g) PSA PSA (g) PSA 1 1

0.5 0.5

0 0 0 1 2 3 4 0 1 2 3 4 Time Period (s) Time Period (s)

(a) (b)

FigureFigure 6.6. ResponseResponse SpectraSpectra forfor ((aa)) DudhaiDudhai (D(D= = 1515 km)km) andand ((bb)) BhachauBhachau (D(D == 1919 km).km).

Next,Next, groundground motionsmotions atat RaparRapar andand Dhori,Dhori, twotwo townstowns locatedlocated atat epicentralepicentral distancesdistances ofof 4646 kmkm andand 4949 kmkm areare analyzed.analyzed. TheThe townstowns areare locatedlocated inin SeismicSeismic ZoneZone 55 ofof thethe IndianIndian codecode withwith aa maximummaximum spectralspectral accelerationacceleration equalequal toto 0.90.9 g.g. FigureFigure7 7 shows shows response response spectra spectra at at these these two two sites. sites. The The response response spectraspectra atat RaparRapar (Figure(Figure7 7a)a) exceeds exceeds the the DBE DBE level level in in the the period period range range of of 0–0.6 0–0.6 s s and and lie lie below below the the DBEDBE levellevel fromfrom 0.5–4 0.5–4 s. s The. The predominant predominant frequency frequency of groundof ground motions motions at Rapar at Rapar is observed is observed to be to 0.11 be s,0.11 respectively, s, respectiv thusely, indicating thus indicating the presence the presence of high-frequency of high-frequency content. The content. predominant The predominant frequency reportedfrequency [39 reported] for Rapar [39 is] 9.6 for Hz. Rapar These is 9.6observations Hz. These indicate observations a hazard indicate to low risea hazard structures. to low While rise thestructures. epicentral While distance the epicentral of Dhori anddistance Rapar of isDhori comparable, and Rapar the is response comparable, spectra the at respo Dhorinse (Figure spectra7b) at areDhori observed (Figure to 7b) be are much observed higher. to It isbe clearlymuch seenhigher. that It theis clearly mean ofseen the that response the mean spectra of the exceeds response the DBEspectra level exceeds across theall time DBE periods, level across indicating all time high period hazards, indicating even to structures high hazard designed even as to per structures seismic codedesigned prescribed as per designseismic procedures.code prescribed Further, desig then procedures. response spectra Further, exceed the response the MCE spectra level till exceed a period the ofMCE 0.8 level s and till lie a around period theof 0.8 MCE s and level lie in around the period the MCE range level of 0.8–4 in the s. period The primary range of reason 0.8–4 for s. The the highprimary response reason spectra for the and high high response observed spectra damage and high in Dhori observed is the damage westward in Dhori directivity is the ofwestward seismic energydirectiv radiatingity of seismic from the energy ruptured radiating fault. fromThe predominant the ruptured frequency fault. The for predominant ground motions frequency at Dhori for is observedground motions to be 0.26 at Dhori s, and is the observed significant to be duration 0.26 s, and is only the significant 6 s, indicating durati a concentrationon is only 6 s, ofindicating seismic energy.a concentration The response of seismic spectra energy. exhibit The sharp response peaks at spectra low time exhibit periods, sharp which peaks indicates at low time that lowperiods, rise structureswhich indicates would that not low survive. rise structures The predominant would not form sur ofvive. construction The predominant in these townsform of consisted construction of low in risethese unreinforced towns consisted masonry of low and rise reinforced unreinforced concrete masonr structures,y and which reinforced are susceptible concrete tostructures, high-frequency which groundare susceptible motions. to high In Rapar-frequency town, ground most (> motions. 75%) buildings In Rapar constructedtown, most (> with 75%) infield-stone, buildings constructed clay and unburnt-brickwith infield-stone, witnessed clay and total unburnt damage,-brick while witnessed many (> total 50%) damage, ordinary while brick structures,many (> 50%) buildings ordinary of brick structures, buildings of the large block and prefabricated type, half-timbered structures witnessed total damage [2]. Also, many (> 50%) reinforced buildings and well-built wooden structures were destroyed. Damage surveys from Dhori town indicated that low rise structures were completely damaged. The observations are consistent with response spectra derived from synthetic ground motions. Overall, both towns were assigned MMI intensity level X [2].

Geosciences 2018, 8, x FOR PEER REVIEW 11 of 17

1.4 3.5

1.2 3

1 2.5 MCE MCE 0.8 2 DBE DBE

0.6 1.5 PSA (g) PSA Geosciences(g) PSA 2018, 8, 429 Mean Spectra Mean Spectra11 of 17 0.4 1

the0.2 large block and prefabricated type, half-timbered0.5 structures witnessed total damage [2]. Also, many0 (> 50%) reinforced buildings and well-built wooden0 structures were destroyed. Damage surveys from Dhori0 town1 indicated2 that low3 rise structures4 were0 completely1 damaged.2 The observations3 4 are consistent with responseTime Period spectra (s) derived from synthetic ground motions.Time Period Overall, (s) both towns were assigned MMI intensity level X [2]. (a) (b) 1.4 3.5

1.2 3

1 2.5 MCE MCE 0.8 2 DBE DBE

0.6 1.5 PSA (g) PSA PSA (g) PSA Mean Spectra Mean Spectra 0.4 1

0.2 0.5

0 0 0 1 2 3 4 0 1 2 3 4 Time Period (s) Time Period (s)

(a) (b)

Figure 7. Response Spectra for (a) Rapar (D = 46 km) and (b) Dhori (D = 49 km).

The twoFig townsure 7. Response of Khavda Spectra and for Adesar (a) Rapar are (D located = 46 km) further and (b away) Dhori at (D epicentral = 49 km). distances equal to 73 km and 78 km. Figure8 shows the response spectra for the two towns. The two towns are locatedThe two in Seismictowns of Zone Khavda 5 of theand Indian Adesar code are withlocated a maximum further away spectral at epicentral acceleration distances equal to equal 0.9 g. to The 73 predominantkm and 78 km. periods Figure for8 shows ground the motionsresponse at spectra Khavda for and the Adesartwo towns. is observed The two totowns be 0.15 are slo andcated 0.19 in s, Seismic respectively. Zone 5 The of thepredominant Indian code frequency with a reportedmaximum for spectral the towns acceleration of Khavda equal and Adesar to 0.9 g. is The6.5 Hz predomiand 3.5nant Hz, per respectivelyiods for ground [39]. Themotions response at Khavda spectra and at A Khavdadesar is (Figure observed8a) to exceeded be 0.15 evens and the0.19 MCE s, respectively.level till a The time pr periodedominant of 0.2 frequency s and lay belowreported the for MCE the leveltowns from of Khavda 0.2–4 s. and The Adesar mean response is 6.5 Hz spectraand 3.5 exceedHz, respectively the DBE level [39]. till The a timeresponse period spectra of 0.6 at s andKhavda lie below (Figure the 8a DBE) exceeded level from even 0.4–4 the s.MCE The level town is till situateda time period towards of 0.2 “west” s and of lay the below fault: the the MCE westward level from directivity 0.2–4 s of. The the mean fault ruptureresponse and spectra propagation exceed in theseismic DBE lev energyel till a is time believed period to of be 0.6 the s and reason lie forbelow high the spectral DBE level acceleration from 0.4– and4 s. The high town observed is situated damage. towardsIn Khavda “west” town, of the many fault: (>the 50%) westward buildings directivity constructed of the fault with rupture infield-stone, and propagation clay and unburnt-brick in seismic energywitnessed is believed heavy to damage be the and reason a few for (~5%) high were spectral completely accelerat destroyedion and high [2]. They observed reported damage. that many In Khavda(> 50%) town, ordinary many brick (> 50%)structures, buildings buildings constructed of the large with block infield and-stone, prefabricated clay and type, unburnt half-timbered-brick witnessedstructures heavy witnessed damage moderate and a few damage. (~5%) were Also, completely many (> destroyed 50%) reinforced [2]. They buildings reported and that well-built many (> 50%)wooden ordinary structures brick witnessedstructures, slightbuildings damage. of the These large block observations and prefabricated are consistent type, with half the-timbered response structuresspectra derived witnessed for themoderate town of damage. Khavda. Also, Damage many corresponding (> 50%) reinforced to intensity buildings level VIII and was well assigned-built to woodenthis town structures [2]. For witnessed the Adesar slight town, damage. although These the derivedobservations response are spectraconsistent (Figure with8 b)the lie response below the specDBEtra derived level, the for town the wastown assigned of Khavda. a high Damage MMI intensity corresponding level of to X intensity [2] on the level basis VIII of observed was assigned damage to thisto prevalent town [2]. structures.For the Adesar In Adesar town, town,although most the (> derived 75%) buildings response constructed spectra (Figure with 8b) infield-stone, lie below the clay DBEand level, unburnt-brick the town was witnessed assigned total a high damage, MMI intensity while many level (> of 50%) X [2] ordinaryon the basis brick of structures,observed damage buildings to prevalentof the large structures. block and In prefabricated Adesar town, type, most half-timbered (> 75%) buildings structures constructed witnessed with total infield damage-stone, [2 ].clay Also, many (> 50%) reinforced buildings and well-built wooden structures were destroyed. The towns of Mandvi and Nakhatrana towns are at more considerable epicentral distances of 111 km and 155 km, respectively. The two towns are in Seismic Zone 5 of the Indian code with a maximum spectral acceleration equal to 0.9 g. Although Mandvi is at a considerable distance from the epicenter, the observed response spectra are high and exhibit “peaky” behavior (Figure9a). The response spectra exceed the DBE level until a time period of 0.4 s, indicating a hazard to low rise structures. The predominant period for ground motions at Mandvi is observed to be 0.14 s indicating Geosciences 2018, 8, 429 12 of 17 the presence of high-frequency content which mainly affects low rise structures, such as unreinforced masonry structures. The predominant frequency is 5.3 Hz [39]. The significant duration is only 9 s, indicating a high concentration of seismic energy. Further, as the spectra exceed the DBE level in the range of 0 s to 0.4 s, it implies that well-designed low-rise masonry and reinforced concrete structures would have experienced immense damage. The coastal town experienced soil amplification as well, and experienced damage corresponding to intensity (MMI) level VII [2]. Figure9b shows that the mean response spectra at Nakhatrana exceeds the DBE level in the low period range of 0–0.2 s and lies below the DBE level at all other periods. The predominant period of ground motions at Nakhatrana is observed to be 0.13 s, indicating the presence of high-frequency waves. Nakhtarana town experienced damage corresponding to intensity (MMI) level VII [2]. Reconnaissance surveys [2] show that in both Mandvi and Nakhtarana towns, many (> 50%) buildings constructed with infield-stone, clay and unburnt-brick witnessed heavy damage and a few (~5%) were completely destroyed. They reported thatGeosciences many 2018 (>, 8 50%), x FOR ordinary PEER REVIEW brick structures, buildings of the large block and prefabricated12 type,of 17 half-timbered structures witnessed moderate damage. Also, many (> 50%) reinforced buildings and well-builtGeosciences 2018 wooden, 8, x FOR structures PEER REVIEW witnessed slight damage. 12 of 17 1.8 1

1.81.6 0.91 0.8 1.61.4 0.9 0.7 1.2 0.8 1.4 MCE MCE 0.70.6 1.21 DBE MCEDBE MCE 0.60.5 0.81 PSA (g) PSA Mean (g) PSA 0.50.4 DBEMean Spectra 0.6 DBE

0.8 Spectra 0.3 PSA (g) PSA PSA (g) PSA 0.4 Mean Spectra 0.60.4 Mean Spectra 0.30.2 0.2 0.4 0.20.1 0.20 0.10 01234 01234 0 0 0 1 Time Period2 (s) 3 4 0 1 Time Period2 (s) 3 4

Time Period (s) Time Period (s) (a) (b) (a) (b) Figure 8. Response Spectra for (a) Khavda (D = 73 km) and (b) Adesar (D = 78 km). Figure 8.8. Response Spectra for (a) Khavda (D(D = 73 km) and ( b) Adesar (D = 78 km) km)..

1.2 1 1.2 1 0.9 1 0.9 1 0.8 0.8 0.7 0.8 0.7 0.8 MCE MCE MCE 0.6 MCE 0.6 0.6 DBE 0.5 DBE 0.6 DBE 0.5 DBE

PSA (g) PSA (g) PSA 0.4 PSA (g) PSA PSA (g) PSA Mean Spectra 0.4 Mean Spectra 0.4 Mean Spectra 0.4 Mean Spectra 0.3 0.3 0.2 0.2 0.2 0.2 0.1 0.1 0 0 0 01234 0 01234 0 1 2 3 4 0 1 2 3 4 Time Period (s) Time Period (s) Time Period (s) Time Period (s)

(a) (b) (a) (b) FigureFigure 9.9. ResponseResponse SpectraSpectra forfor ((aa)) MandviMandvi (D(D == 111111 km)km) andand ((bb)) NakhatranaNakhatrana (D(D == 155155 km).km). Figure 9. Response Spectra for (a) Mandvi (D = 111 km) and (b) Nakhatrana (D = 155 km). The towns of Mandvi and Nakhatrana towns are at more considerable epicentral distances of The towns of Mandvi and Nakhatrana towns are at more considerable epicentral distances of 111 km and 155 km, respectively. The two towns are in Seismic Zone 5 of the Indian code with a 111 km and 155 km, respectively. The two towns are in Seismic Zone 5 of the Indian code with a maximum spectral acceleration equal to 0.9 g. Although Mandvi is at a considerable distance from maximum spectral acceleration equal to 0.9 g. Although Mandvi is at a considerable distance from the epicenter, the observed response spectra are high and exhibit “peaky” behavior (Figure 9a). The the epicenter, the observed response spectra are high and exhibit “peaky” behavior (Figure 9a). The response spectra exceed the DBE level until a time period of 0.4 s, indicating a hazard to low rise response spectra exceed the DBE level until a time period of 0.4 s, indicating a hazard to low rise structures. The predominant period for ground motions at Mandvi is observed to be 0.14 s indicating structures. The predominant period for ground motions at Mandvi is observed to be 0.14 s indicating the presence of high-frequency content which mainly affects low rise structures, such as unreinforced the presence of high-frequency content which mainly affects low rise structures, such as unreinforced masonry structures. The predominant frequency is 5.3 Hz [39]. The significant duration is only 9 s, masonry structures. The predominant frequency is 5.3 Hz [39]. The significant duration is only 9 s, indicating a high concentration of seismic energy. Further, as the spectra exceed the DBE level in the indicating a high concentration of seismic energy. Further, as the spectra exceed the DBE level in the range of 0 s to 0.4 s, it implies that well-designed low-rise masonry and reinforced concrete structures range of 0 s to 0.4 s, it implies that well-designed low-rise masonry and reinforced concrete structures would have experienced immense damage. The coastal town experienced soil amplification as well, would have experienced immense damage. The coastal town experienced soil amplification as well, and experienced damage corresponding to intensity (MMI) level VII [2]. Figure 9(b) shows that the and experienced damage corresponding to intensity (MMI) level VII [2]. Figure 9(b) shows that the mean response spectra at Nakhatrana exceeds the DBE level in the low period range of 0–0.2 s and mean response spectra at Nakhatrana exceeds the DBE level in the low period range of 0–0.2 s and lies below the DBE level at all other periods. The predominant period of ground motions at lies below the DBE level at all other periods. The predominant period of ground motions at Nakhatrana is observed to be 0.13 s, indicating the presence of high-frequency waves. Nakhtarana Nakhatrana is observed to be 0.13 s, indicating the presence of high-frequency waves. Nakhtarana town experienced damage corresponding to intensity (MMI) level VII [2]. Reconnaissance surveys [2] show that in both Mandvi and Nakhtarana towns, many (> 50%) buildings constructed with

Geosciences 2018, 8, x FOR PEER REVIEW 13 of 17

town experienced damage corresponding to intensity (MMI) level VII [2]. Reconnaissance surveys [2] show that in both Mandvi and Nakhtarana towns, many (> 50%) buildings constructed with Geosciences 2018, 8, 429 13 of 17 infield-stone, clay and unburnt-brick witnessed heavy damage and a few (~5%) were completely destroyed. They reported that many (> 50%) ordinary brick structures, buildings of the large block Figureand prefabricated 10 shows thetype, response half-timbered spectra structures for ground witnessed motions moderate generated damage. for MorbiAlso, many town (> situated 50%) in reinforced buildings and well-built wooden structures witnessed slight damage. seismic zone 4 [15] with a maximum spectral acceleration equal to 0.6 g. The response spectra exhibit Figure 10 shows the response spectra for ground motions generated for Morbi town situated in very peaky behavior at short periods, followed by a sharp drop. The mean response spectra exceed seismic zone 4 [15] with a maximum spectral acceleration equal to 0.6 g. The response spectra exhibit the DBEvery levelpeaky in behavior the period at short range periods, of 0.3 followed s, indicating by a sharp the hazarddrop. The to mean low riseresponse structures, spectra particularly,exceed 1–3 storythe DBE structures. level in the The period town range experienced of 0.3 s, indicating damage the corresponding hazard to low to rise intensity structures, (MMI) particularly, level VII [2]. The Morbi1–3 story town structures. has unconsolidated The town experienced soil cover damage [9] whichcorresponding caused to amplification intensity (MMI) of groundlevel VII motions.[2]. SeveralThe three Morbi story town structures has unconsolidated collapsed soil in Morbi cover town.[9] which In Morbi,caused manyamplification (> 50%) of buildings ground motions. constructed withSeveral infield-stone, three story clay structures and unburnt-brick collapsed in witnessed Morbi town. heavy In Morbi, damage many and (> 50%) a few buildings (~5%) wereconstructed completely destroyedwith infield-stone, [2]. Many (> clay 50%) and ordinary unburnt-brick brick witnessed structures, heavy buildings damage of and the a few large (~5% block) were and completely prefabricated type,destroyed half-timbered [2]. Many structures (> 50%) witnessedordinary brick moderate structur damage.es, buildings Also, of the many larg (>e block 50%) and reinforced prefabricated buildings type, half-timbered structures witnessed moderate damage. Also, many (> 50%) reinforced buildings and well-built wooden structures witnessed slight damage. These observations are consistent with and well-built wooden structures witnessed slight damage. These observations are consistent with the derivedthe derived response response spectra spectra for for Morbi Morbi town. town. Figure 11 11 shows shows the the pseudo-spectral pseudo-spectral acceleration acceleration (PSA) (PSA) at 5%at damping 5% damping for for Lalpur Lalpur and and Dwarka, Dwarka, twotwo townstowns located located in in Seismic Seismic Zone Zone 4 [15] 4 [ 15with] with a maximum a maximum spectralspectral acceleration acceleration equal equal to to 0.6 0.6 g. g. The The mean mean responseresponse spectra spectra at atLalpur Lalpur and and Dwarka Dwarka does does not cross not cross the DBEthe DBE and and MCE MCE levels. levels. However, However, damage damage surveyssurveys indicate indicate damage damage in Dwarka in Dwarka port port area areadue to due to amplificationamplification of ground of ground motion, motion, surface surface wave wave generation generation and and their their trapping trapping by theby weatheredthe weathered surficial layersurficial of the island layer of [9 the]. The island response [9]. The spectra response for sp groundectra for motionsground motions generated generated for other for townsother towns in Zone 4 lie belowin Zone the 4 codelie below prescribed the code levels prescribed and hencelevels and are nothence discussed are not discussed in detail. in detail.

1 0.9 0.8 0.7 0.6 0.5 MCE

PSA (g) PSA DBE 0.4 Mean Spectra 0.3 0.2 0.1 0 0 0.5 1 1.5 2 2.5 3 3.5 4 Time Period (s)

Geosciences 2018, 8, x FOR PEER REVIEW 14 of 17 FigureFigure 10. 10.Response Response Spectra for for Morbi Morbi (Zone (Zone 4). 4). 0.7 0.7

0.6 0.6

0.5 0.5 MCE MCE 0.4 0.4 DBE DBE

0.3 0.3 Mean Spectra PSA (g) PSA PSA(g) Mean Spectra 0.2 0.2 0.1 0.1 0 0 0 1 2 3 4 0 1 2 3 4 Time Period (s) Time Period (s)

(a) (b)

Figure 11.11. Response Spectra for (a)) LalpurLalpur andand ((bb)) DwarkaDwarka (Zone(Zone 4).4).

The response spectra for towns in Zone 3 having MCE level of 0.45 g [15] were typically much lower than the DBE levels. These towns were assigned low-intensity(MMI) levels of IV. However, the damage to multistory structures in cities situated far away from the epicenter, e.g., Ahmedabad and , could be attributed to deficient structural designs or poor construction practices. Indeed, the damage surveys [2] report the failure of columns at the ground-story level of these buildings. There were no walls at the ground story level which was intended for parking. As the stiffness of the ground story was much less as compared to the upper stories, the buildings collapsed due to the soft story effect. The damage to buildings in these cities was also partly influenced by the presence of alluvium soil at some locations. In areas having thick layers of alluvium soil, more damage was observed to multistory buildings as compared to similar structures in areas having hard rock [2,9]. The predominant frequency for Ahmedabad was reported as 2 Hz [39] which corresponds to structures with 4–5 stories. Ahmedabad was assigned a damage intensity (MMI) of VII and VI while Surat was assigned a damage intensity (MMI) level of VI. Despite the response spectra being much lower than the code prescribed spectra, other towns in Zone 3 such as , Gandhinagar, Surendranagar, Viramgam experienced structural damage corresponding to intensity (MMI) level of VI indicating deficiencies in design and construction practices.

3. Discussion The response spectra of ground motions for towns situated at small epicentral regions, such as Dudhai and Bhachau, exceed both the MCE and DBE levels, and exhibit sharp peaks in the low frequency region. These observations conform with damage surveys which indicate that in such towns, most low rise structures witnessed total devastation and many reinforced concrete buildings were damaged. The effect of western directivity of the fault rupture is observed in some towns which experienced high PGAs. In towns situated at more considerable epicentral distances, such as Mandvi and Nakhtarana, the response spectra of ground motions exceeded the DBE level mostly in the short period ranges, causing damage to many low rise structures made of infield-stone, clay, brick and reinforced concrete. In Mandvi, the effect of soil amplification caused higher structural damage. Response spectra for towns situated very far away from the epicenter were much lower than the DBE levels: Observed damage in these towns is attributed to poor quality of construction and deficiency in the seismic design of structures. In these towns, several reinforced concrete structures were damaged due to the soft story effect.

4. Conclusions

Geosciences 2018, 8, 429 14 of 17

The response spectra for towns in Zone 3 having MCE level of 0.45 g [15] were typically much lower than the DBE levels. These towns were assigned low-intensity(MMI) levels of IV. However, the damage to multistory structures in cities situated far away from the epicenter, e.g., Ahmedabad and Surat, could be attributed to deficient structural designs or poor construction practices. Indeed, the damage surveys [2] report the failure of columns at the ground-story level of these buildings. There were no walls at the ground story level which was intended for parking. As the stiffness of the ground story was much less as compared to the upper stories, the buildings collapsed due to the soft story effect. The damage to buildings in these cities was also partly influenced by the presence of alluvium soil at some locations. In areas having thick layers of alluvium soil, more damage was observed to multistory buildings as compared to similar structures in areas having hard rock [2,9]. The predominant frequency for Ahmedabad was reported as 2 Hz [39] which corresponds to structures with 4–5 stories. Ahmedabad was assigned a damage intensity (MMI) of VII and VI while Surat was assigned a damage intensity (MMI) level of VI. Despite the response spectra being much lower than the code prescribed spectra, other towns in Zone 3 such as Rajkot, Gandhinagar, Surendranagar, Viramgam experienced structural damage corresponding to intensity (MMI) level of VI indicating deficiencies in design and construction practices.

3. Discussion The response spectra of ground motions for towns situated at small epicentral regions, such as Dudhai and Bhachau, exceed both the MCE and DBE levels, and exhibit sharp peaks in the low frequency region. These observations conform with damage surveys which indicate that in such towns, most low rise structures witnessed total devastation and many reinforced concrete buildings were damaged. The effect of western directivity of the fault rupture is observed in some towns which experienced high PGAs. In towns situated at more considerable epicentral distances, such as Mandvi and Nakhtarana, the response spectra of ground motions exceeded the DBE level mostly in the short period ranges, causing damage to many low rise structures made of infield-stone, clay, brick and reinforced concrete. In Mandvi, the effect of soil amplification caused higher structural damage. Response spectra for towns situated very far away from the epicenter were much lower than the DBE levels: Observed damage in these towns is attributed to poor quality of construction and deficiency in the seismic design of structures. In these towns, several reinforced concrete structures were damaged due to the soft story effect.

4. Conclusions The 2001 Gujarat earthquake was one of the most destructive intraplate earthquakes ever recorded. The maximum felt intensity was X on the Modified Mercalli Intensity (MMI) scale, and a large percentage of buildings in the Kutch region were damaged. However, no strong ground motion records are available for this earthquake. Only PGA values are available from structural response recorders at thirteen sites. In this paper, synthetic ground motions for the 2001 Gujarat scenario earthquake were generated, using the modified stochastic finite-fault method. Available recorded data are used to validate PGA values of the synthetic ground motions. Upon validation, ground motions at other locations were also generated and analyzed. The characteristics of the ground motions such as peak ground acceleration (PGA), peak ground velocity (PGV), frequency content, significant duration, and energy content were also analyzed. Ground motions have low values of Tp, i.e., they contain high frequency content. Such waves could be particularly damaging to low rise structures. Response spectra of ground motions for towns situated in Seismic Zone 5 exceeded even the code prescribed “maximum considered earthquake” spectra levels. The code spectra for Zone 5 thus seem un-conservative. The same was observed [44] while studying the effect of geological settings on response spectra. Their study shows that the acceleration response spectrum in the current Indian code for Gujarat region underestimates the seismic forces at short periods. Further, the response spectra show peaks in low period ranges. Consequently, low rise structures in the Kutch region, designed as Geosciences 2018, 8, 429 15 of 17 per existing seismic codes of India, are highly vulnerable to damage under such scenario earthquakes. Response spectra for towns situated in seismic zone 3 did not exceed the code prescribed levels. Structural damage observed in such towns in seismic zone 3, far away from the epicenter, may not be attributed to the observed low seismic intensity (MMI) levels but rather to poor construction practices and non-adherence of structural designs to seismic code standards.

Author Contributions: Conceptualization, J.V. and K.S.; methodology, J.V, K.S. and S.C.; validation, J.V, K.S. and S.C.; formal analysis, J.V.; investigation, J.V.; resources, K.S.; writing—original draft preparation, J.V.; writing—review and editing, K.S. and S.C.; supervision, K.S.; Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflict of interest.

References

1. Nagamani, D.; Mandal, P. Estimation of earthquake source parameters in the Kachchh seismic zone, Gujarat, India, using three component S-wave spectra. J. Earth Syst. Sci. 2017, 126, 74. [CrossRef] 2. Sinvhal, A.; Bose, P.R.; Prakash, V.; Bose, A.; Saraf, A.K.; Sinvhal, H. Isoseismals for the Kutch earthquake of 26th January 2001. J. Earth Syst. Sci. 2003, 112, 375–383. [CrossRef] 3. Chopra, S.; Kumar, D.; Rastogi, B.K. Estimation of strong ground motions for 2001 Bhuj (Mw 7.6), India Earthquake. Pure Appl. Geophys. 2010, 167, 1317–1330. [CrossRef] 4. Gupta, H.K.; Harinarayana, T.; Kousalya, M.; Mishra, D.C.; Mohan, I.; Purnachandra Rao, N.; Raju, P.S.; Rastogi, B.K.; Reddy, P.R.; Sarkar, D. Bhuj earthquake of 26 January 2001. J. Geol. Soc. India 2001, 72, 245–252. 5. Gupta, H.K.; Purnachandra Rao, N.; Rastogi, B.K.; Sarkar, D. The deadliest intraplate earthquake: Perspectives. Science 2001, 291, 2101–2102. [CrossRef][PubMed] 6. Rastogi, B.K.; Gupta, H.K.; Mandal, P.; Satyanarayana, H.V.S.; Kousalya, M.; Raghavan, R.; Jain, R.; Sarma, A.N.S.; Kumar, N.; Satyamurty, C. The deadliest stable continental region earthquake occurred near Bhuj on 26 January 2001. J. Seismol. 2001, 5, 609–615. [CrossRef] 7. Rajendran, K.; Rajendran, C.P.; Thakkar, M.; Tuttle, M.P. The 2001 Kutch (Bhuj) earthquake: Coseismic surface features and their significance. Curr. Sci. 2001, 80, 1397–1405. 8. Michetti, A.M.; Esposito, E.; Guerrieri, L.; Porfido, S.; Serva, L.; Tatevossian, R.; Vittori, E.; Audemard, F.; Azuma, T.; Clague, J.; Comerci, V. Environmental seismic intensity scale-ESI 2007. Mem. Descr. Della Carta Geol. d’Italia 2007, 74, 41. 9. Narayan, J.P.; Sharma, M.L. Effect of Local Geology on Damage Severity during Bhuj, India earthquake. In Proceedings of the Thirteenth World Conference on Earthquake Engineering, Vancouver, BC, , 1–4 August 2004; Paper No.2042. 10. Chatelain, J.L.; Guillier, B.; Parvez, I.A. False Site Effects: The Anjar Case, following the 2001 Bhuj (India) Earthquake. Seismol. Res. Lett. 2008, 79, 816–819. [CrossRef] 11. Cramer, C.H.; Kumar, A. 2001 Bhuj, India, earthquake engineering seismoscope recordings and Eastern North America ground-motion attenuation relations. Bull. Seismol. Soc. Am. 2003, 93, 1390–1394. [CrossRef] 12. Biswas, S.K. Regional tectonic framework, structure and evolution of the western marginal basins of India. Tectonophysics 1987, 135, 307–327. [CrossRef] 13. Biswas, S.K. A review of structure and tectonics of Kutch basin, western India, with special reference to earthquakes. Curr. Sci. 2005, 88, 1592–1600. 14. Talwani, P.; Gangopadhyay, A. Tectonic Framework of the Kutch Earthquake of 26 January 2001. Seismol. Res. Lett. 2001, 72, 336–345. [CrossRef] 15. Bureau of Indian Standards. IS 1893 Indian Standard Criteria for Earthquake Resistant Design of Structures: Part 1– General Provisions and Buildings; BIS: New Delhi, India, 2002. 16. Yadav, R.B.S.; Tripathi, J.N.; Rastogi, B.K.; Chopra, S. Probabilistic assessment of earthquake hazard in Gujarat and adjoining region of India. Pure and Appl. Geophy. 2008, 165, 1813–1833. [CrossRef] 17. Quittmeyer, R.C.; Jacob, K.H. Historical and modern seismicity of , Afghanistan, northwestern India, and southeastern Iran. Bull. Seismol. Soc. Am. 1979, 69, 773–823. 18. Bendick, R.; Bilham, R.; Fielding, E.; Gaur, V.K.; Hough, S.E.; Kier, G.; Kulkarni, M.N.; Martin, S.; Mukul, M. The 26 January 2001 “Republic Day” Earthquake, India. Seismol. Res. Lett. 2001, 72, 328–335. [CrossRef] Geosciences 2018, 8, 429 16 of 17

19. Motazedian, D.; Atkinson, G.M. Stochastic finite-fault modeling based on dynamic corner frequency. Bull. Seismol. Soc. Am. 2005, 95, 995–1010. [CrossRef] 20. Boore, D. Stochastic simulation of high-frequency ground motions based on seismological models of the radiated spectra. Bull. Seismol. Soc. Am. 1983, 73, 1865–1894. 21. Anderson, J.; Hough, S. A model for the shape of the Fourier amplitude spectrum of acceleration at high frequencies. Bull. Seismol. Soc. Am. 1984, 74, 1969–1993. 22. Beresnev, I.A.; Atkinson, G.M. Modeling finite fault radiation from the ωn spectrum. Bull. Seismol. Soc. Am. 1997, 87, 67–84. 23. Negishi, H.; Mori, J.; Sato, T.; Singh, R.; Kumar, S.; Hirata, N. Size and orientation of the fault plane for the 2001 Gujarat, India earthquake (Mw 7.7) from aftershock observations: A high stress drop event. Geophy. Res. Lett. 2002, 29, 1949. [CrossRef] 24. Schweig, E.; Gomberg, J.; Petersen, M.; Ellis, M.; Bodin, P.; Mayrose, L.; Rastogi, B.K. The Mw 7.7 Bhuj Earthquake: Global lessons for earthquake hazard in intra-plate regions. J. Geol. Soc. India 2003, 61, 277–282. 25. Singh, S.K.; Bansal, B.K.; Bhattacharya, S.N.; Pacheco, J.F.; Dattarayam, R.S.; Ordaz, M.; Suresh, G.; Kamal; Hough, S.E. Estimation of Ground Motion for Bhuj (26 January 2001; Mw 7.6) and for future Earthquakes in India. Bull. Seismol. Soc. Am. 2003, 93, 353–370. [CrossRef] 26. Rastogi, B.K. Damage due to the Mw 7.7 Kutch, India earthquake of 2001. Tectonophysics 2004, 390, 85–103. [CrossRef] 27. Mandal, P.; Rastogi, B.K.; Satyanarayana, H.V.S.; Kousalya, M.; Vijayraghvan, R.; Satyamurthy, C.; Raju, I.P.; Sarma, A.N.S.; Kumar, N. Characterization of causative fault system for the 2001 Bhuj earthquake of Mw 7.7. Tectonophysics 2004, 378, 105–121. [CrossRef] 28. Gahalaut, V.K.; Burgmann, R. Constraints on the Source Parameters of the 26 January 2001 Bhuj, India, Earthquake from Satellite Images. Bull. Seismol. Soc. Am. 2004, 94, 2407–2413. [CrossRef] 29. Bodin, P.; Horton, S. Source parameters and tectonic implications of aftershocks of the Mw 7.6 Bhuj earthquake of January 26, 2001. Bull. Seismol. Soc. Am. 2004, 94, 818–827. [CrossRef] 30. Atkinson, G.M.; Boore, D.M. Ground Motion Relations for Eastern North America. Bull. Seismol. Soc. Am. 1995, 85, 17–30. 31. Bodin, P.; Malagnini, L.; Akinci, A. Ground-Motion Scaling in the Kachchh Basin, India, Deduced from Aftershocks of the 2001 Mw 7.6 Bhuj Earthquake. Bull. Seismol. Soc. Am. 2004, 94, 1658–1669. [CrossRef] 32. Yagi, Y.; Kikuchi, K. Western India Earthquake. Available online: http://equake-rc.info/static/srcmod_ archives/s2001BHUJINyagi.html (accessed on 1 June 2016). 33. USGS. Available online: https://earthquake.usgs.gov/earthquakes/eventpage/usp000a8ds (accessed on 26 January 2001). 34. Frankel, A.; Mueller, C.; Barnhard, T.; Perkins, D.; Leyendecker, E.V.; Dickman, N.; Hanson, S.; Hopper, M. Seismic-Hazard Maps for the Conterminous ; U.S. Geological Survey: Reston, VA, USA, 1997; scale 1: 7,000,000. 35. Joyner, W.B.; Boore, D.M. Recent developments in earthquake ground motion estimation. In Proceedings of the 6th International Conference on Seismic Zonation, Palm Springs, CA, USA, 12–15 November 2000. 36. Geologic Map of India. Sixth Eds, Geological Survey of India; GSI: Kolkata, India, 1962; scale 1: 2,000,000. 37. Boore, D.M.; Joyner, W.B. Site amplifications for generic rock sites. Bull. Seismol. Soc. Am. 1997, 87, 327–341. 38. Atkinson, G.M.; Boore, D.M. Earthquake ground motion prediction equations for Eastern North America. Bull. Seismol. Soc. Am. 2006, 96, 2181–2205. [CrossRef] 39. Chopra, S.; Kumar, D.; Rastogi, B.K.; Choudhury, P.; Yadav, R.B.S. Estimation of site amplification functions in Gujarat region, India. Nat. Hazards 2013, 65, 1135–1155. [CrossRef] 40. Choudhury, P.; Chopra, S.; Roy, K.S. Site Classification for Strong Motion Stations in Gujarat, India using response spectral ratio. Soil Dyn. Earthq. Eng. 2016, 87, 138–150. [CrossRef] 41. Di Alessandro, C.; Bonilla, L.F.; Boore, D.M.; Rovelli, A.; Scotti, O. Predominant-Period Site Classification for Response Spectra Prediction Equations in . Bull. Seismol. Soc. Am. 2012, 102, 680–695. [CrossRef] 42. Rathje, E.M.; Abrahamson, N.A.; Bray, J.D. Simplified Frequency Content Estimates of Earthquake Ground Motions. ASCE J. Geotech. Geoenvironmental Eng. 1998, 124, 150–159. [CrossRef] Geosciences 2018, 8, 429 17 of 17

43. Hough, S.E.; Martin, S.; Bilham, R.; Atkinson, G.M. The 26 January 2001 M. 7.6 Bhuj, India, Earthquake: Observed and Predicted Ground Motions. Bull. Seismol. Soc. Am. 2002, 92, 2061–2079. [CrossRef] 44. Chopra, S.; Choudhury, P. A study of response spectra for different geological conditions in Gujarat, India. Soil Dyn. Earthq. Eng. 2011, 31, 1551–1564.

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).