Probabilistic seismic hazard assessment of the …...G. C¸ . Ince: Probabilistic seismic hazard...

Nat. Hazards Earth Syst. Sci., 12, 3483–3493, 2012www.nat-hazards-earth-syst-sci.net/12/3483/2012/doi:10.5194/nhess-12-3483-2012© Author(s) 2012. CC Attribution 3.0 License.

Natural Hazardsand Earth

System Sciences

Probabilistic seismic hazard assessment of the historical peninsulaof Istanbul

G. C. Ince

Division of Civil Engineering, Department of Geotechnical Engineering, Faculty of Engineering, Aksaray University,68100 Aksaray, Turkey

Correspondence to:G. C. Ince ([email protected])

Received: 16 April 2012 – Revised: 18 October 2012 – Accepted: 20 October 2012 – Published: 22 November 2012

Abstract. In order to design buildings that are resistant toearthquakes, first it is necessary to determine the parametersof ground motion. In this study, the earthquake seismic haz-ard analysis of the Old City Districts of Istanbul (Fatih andEminonu) was probabilistically defined. For the analysis, thestudy zone was divided into 307 cells of 250× 250 m us-ing geographical information systems, and these cells wereused in the mapping of all the data obtained. Then, fora building lifetime of 50 yr, the acceleration parameters ofearthquake ground motions, peak ground acceleration, peakground velocity, and spectral acceleration values of 0.2 s and1 s were obtained at the bedrock level according to 10 % and40 % exceedances. Additionally, in order to produce the ar-tificial acceleration-time records of the ground movementin accordance with the NEHRP acceleration spectrum, theTARSCHTS computer simulation program was utilized. Theresults of the analysis showed that for the 10 % probabilityof exceedance, the peak bedrock acceleration values rangedfrom 0.30 g to 0.40 g, and for the 40 % exceedance probabil-ity the acceleration values ranged from 0.22 g to 0.17 g. TheSs 10 % exceedance probability, calculated according to thespectral acceleration parameter, ranged from 0.67 g to 0.85 gand the spectral acceleration parameterS1 varied between0.22 g–0.28 g. TheSs 40 % exceedance probability, calcu-lated according to the spectral acceleration parameter, rangedfrom 0.46 g to 0.38 g and the spectral acceleration parameterS1 varied from 0.12 g to 0.14 g.

1 Introduction

Due to their destructive and damaging effects on buildings,the impact of earthquakes should be taken into serious con-sideration while designing buildings. The purpose of design-ing earthquake resistant structures is to construct them in away that overcomes a certain level of vibration without thestructure incurring excessive damage. The level of groundshaking is defined by the design ground motion which canbe characterized by certain ground motion parameters. Thedetermination of the design ground motion constitutes oneof the most difficult and important problems in geotechnicalearthquake engineering.

When undertaking studies related to earthquakes, the pri-mary requirement is to carry out the assessment by takinginto consideration all the tectonic elements which could havean impact on the studied area and create an earthquake. Forthe accuracy and reliability of such a study, it is necessary forthe disciplines related to geology to work together in orderto determine the design ground motion. First it is necessaryto compile all the instrumental and historical information onpast seismic activity; second, to determine the presence ofearthquake-generating sources by investigating the area geo-logically and morphologically; and third, to state the futureearthquake hazard mathematically by expressing the charac-teristics of the source.

There are two methods commonly used in the determina-tion of the seismic hazard. One is probabilistic seismic haz-ard analysis, which takes into account all earthquake scenar-ios able to affect the area under investigation. The hazardresulting from this analysis is expressed with ground motionparameters such as the largest ground acceleration and spec-tral acceleration under reference ground conditions. Another

Published by Copernicus Publications on behalf of the European Geosciences Union.

3484 G. C. Ince: Probabilistic seismic hazard assessment of the historical peninsula of Istanbul

method is deterministic seismic hazard analysis, which isusually undertaken after the probabilistic analysis. This isbecause the deterministic earthquake scenarios used to cal-culate the separation of the composite probabilistic hazard(deaggregation), which provides the greatest contribution toassessing earthquake risk in a specific region, can be obtainedfrom the determination of earthquake sources. As a resultof the deterministic analysis, ground motion parameters orartificially-forced ground motion accelerograms can be ob-tained (Erdik et al., 2003).

2 Probabilistic seismic hazard analysis

2.1 Properties of probabilistic hazard assessment

Probabilistic seismic hazard analysis takes into considerationall the earthquake sources that may affect the study area. Thisanalysis can perform calculations according to the desiredexceedance probability, considering the annual exceedanceprobabilities for each scenario earthquake. Given an aver-age 50 yr lifetime for a building, adequate security can beprovided for buildings with a 10 % exceedance probability.However, it is necessary to make assessments for strategi-cally important structures, such as hospitals and schools, formajor earthquakes with a lower probability of exceedance.The earthquake hazard for recurrence times (shorter than theaverage recurrence periods of large earthquakes on earth-quake source) increases according to the exceedance prob-ability. The main reason for this increase is that the prob-ability of large earthquakes increases with the large ex-ceedance probabilities. The seismic hazard for a longer re-currence duration than the average recurrence period of alarge earthquake increases depending on the probabilities ofexceedance. In this case, the statistical errors (standard devi-ation) in attenuation relations are the main cause of the in-crease. Statistically, the more large earthquakes occur in thesource above the average value, the greater the possibility ofearthquake ground motions. In other words, the probabilis-tic seismic hazard in the regions with high seismic activityis larger than in the regions with low seismic activity, eventhough the magnitude of the largest earthquake they can pro-duce is the same size. This situation creates a conflict with thedeterministic seismic hazard estimations (Erdik et al., 1999).

In order to determine earthquake recurrence relations inthe source zone, the recurrence frequency of different mag-nitude groups are organized in the time interval where thecomplete data for all magnitude groups are gathered. Theempirical recurrence relationship for earthquakes was devel-oped by Gutenberg and Richter (1944) using the data fromearthquakes in Southern California. After arranging the datagathered according to the number of earthquakes in excessof different magnitudes, they definedM magnitude of earth-quakes asλm by dividing the exceedance numbers of eachmagnitude by time. Predictably, the annual exceedance rates

of small earthquakes are greater than major earthquakes. Thereverse of the average exceeding rate of earthquakes at acertain magnitude is usually defined as the return period ofearthquakes over that size. The logarithm of the annual ex-ceedance rates of the earthquakes in Southern California,then its graph was drawn according to earthquake magnitude.The Gutenberg-Richter (1944) law for earthquake recurrenceis expressed as follows:

Logλm = a − bm. (1)

This is the average annual exceedance rate of the earth-quake; 10a is the average number of annual occurrences ofearthquakes with magnitudes equal to or greater than zero;andb is the coefficient representing the relative likelihoodof occurrences for minor and major earthquakes. Based onglobal data, Tsapanos (1990) suggested that b-values areclosely related with the tectonic regime of an area.

One of the important steps in probabilistic seismic hazardanalysis is the determination of earthquake ground motionin the studied area using ground motion attenuation models.Source, progress line and area features are utilized in atten-uation models in which finite element and finite differencemethods are used.

The most widely used ground movement predictor in seis-mic hazard studies is the horizontal component of the max-imum ground acceleration. This is because the horizontalcomponent is the best parameter to define the state of groundmotion and it controls the structure behaviour. In many ofthe attenuation relations, the maximum ground accelerationis expressed with magnitude (M), distance (R) and localground conditions. Magnitude is a limited measure of dis-placement. The description used for the magnitude shouldbe consistent within itself to determine the attenuation re-lationships, the collection of frequency-magnitude data, andthe maximum magnitude. Maximum ground acceleration at-tenuation relationships are usually based on the concept ofa local magnitude. The distance parameter (R) used in theattenuation relations can be the distance to the focal point,the epicentre, the energy discharge centre, the fault surface,and fault epicentre. The definition of the distance parame-ter (R) plays an important role, especially in regions closeto the fault, and this definition must be in compliance withlocal features. The earthquakes that occur in Turkey are of-ten shallow, focused and demonstrate superficial ruptures. Insuch regions, it is more appropriate to use the distance fromthe local area to the fault line. In the majority of the atten-uation relations, which give the evaluation of the maximumground acceleration according toM and R, the maximumground acceleration shows a log-normal distribution, and theaverage value is stated as:

PGA= b1exp(b2M)(R + b4)b3. (2)

The standard deviation andσlogPGA, b1, b2, b3, b4 coeffi-cients in this equation are the regression constants. Many at-tenuation correlations have been developed for earthquakes

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G. C. Ince: Probabilistic seismic hazard assessment of the historical peninsula of Istanbul 3485

Fig. 1.Tectonic Features (from McKenzie, 1972).

with a medium distance (20–30 km) from the fault. Theseinclude correlations developed by McGuire (1978), Dono-van (1973), Ambraseys (1975), Esteva and Villaverde (1973)and Cornell et al. (1979).

In probabilistic earthquake hazard calculations, it is ac-cepted that earthquakes occur totally probabilistically andmemoryless (time independent) and at a certain periodicity(time dependent). In time-dependent models, the possibilityof a new major earthquake occurrence increases as the timesince the last major earthquake increases (defined as whenall of the fault segment is broken). The distinctive featureof the time-dependent model compared to other models isthe probability density function of the recurrence interval ofcharacteristic earthquakes. Time-independent methods suchas the homogeneous Poisson model can be used for largeregional seismic sources or tectonic units where the neces-sary information for time-dependent modelling is not avail-able. In the Poisson model, the possibility of the next earth-quake occurrence does not depend on the time of the pre-vious earthquake. The intensive paleoseismic and historicalearthquake research conducted on many tectonic elements,including the North Anatolian fault line, show that the majorcharacteristic earthquakes on these faults occur almost pe-riodically (Schwartz and Coppersmith, 1984), and thereforeit is more appropriate to use the time-dependent modellingmethod (Recurrence Method).

2.2 Seismic source zones for the region

The information from the earthquake hazard study in Turkeyand neighbouring regions for the Global Seismic Hazard As-sessment Program (GSHAP) (Erdik et al., 1999) was usedas source zoning in the probabilistic assessment of the studyarea. In this project, the seismicity in the region was basedon 307 cells that were evaluated for the first time. Turkey islocated in the Mediterranean-Himalayan seismic belt in a re-gion where there are many small plates between larger plates.According to historical earthquake records, Turkey has been

Fig. 2. Historical Seismicity with the Major Tectonic Features(Erdik et al., 1999).

Fig. 3. Instrumental Seismicity with the Major Tectonic Features(Erdik et al., 1999).

consistently been affected by earthquakes since 2000 BC.Figure 1 shows the location of Turkey in relation to the threelarge Eurasian, African and Arabian plates. It can be seenthat a large part of Anatolia is situated on a small portion ofthe Eurasian plate.

The historical and instrumental seismicity records of theregion were compiled again under the GSHAP project, andare shown in Figs. 2 and 3. Within the scope of the project,seismic hazard zones were created by evaluating both theseismicity and tectonic state of the region (Fig. 4), and therecurrence relations for these zones were defined using theGutenberg-Richter relation (Table 1). The earthquake sourcezones 18, 19, 20, 23, 26 and 27, which were thought to affectthe study area, were taken into account in the analyses.

3 The seismic hazard assessment of the study areaaccording to the probabilistic method

3.1 Zone under investigation

The study was undertaken in the districts of Fatih and Emi-nonu, Istanbul, Turkey as shown in Fig. 5. Istanbul has

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Figure 3. Instrumental Seismicity with the Major Tectonic Features (Erdik et al., 1999)

Figure 4. Seismic Source Zones together with the Major Tectonic Features (Erdik et al., 1999)

Fig. 4.Seismic Source Zones together with the Major Tectonic Fea-tures (Erdik et al., 1999).

Table 1.The recurrence relations obtained from the GSHAP project(GSHAP, 1999).

Zone Name a b

Zone 18 3.318 −0.684Zone 19 3.9734 −0.8138Zone 20 2.3912 −0.5755Zone 23 0.9396 −0.4326Zone 26 5.0540 −0.8457Zone 27 2.1720 −0.5740

experienced many strong earthquakes in its history and suf-fered extensive damage. The area covering the districts ofFatih and Eminonu is known as the historical peninsula andcontains many significant historial buildings. The districtscomprise a commercial centre and together they are one ofthe most densely populated locations of Istanbul city. Thestudy zone was divided into cells of 250× 250 m, then num-bered to determine the seismic hazard for each cell and tocreate bedrock acceleration parameters (Fig. 6).

3.2 Recurrence relationships for the region

Earthquake occurrence parameters for the area, consistingof the Fatih and Eminonu districts (i.e. annual occurrencerelations depending on magnitude), are shown using theGutenberg–Richter relations (1944) in Eq. (1).λm was takenas 7.5, thea andb regression coefficients were taken fromTable 1 and entered into the appropriate places in SeisriskIIIapplication.

3.3 Selected attenuation relationships for the region

For the PGA

The earthquake sources in the study area are generally near-focus (shallow) earthquakes with the depth usually varyingfrom around 0 to 30 km. These shallow earthquakes affect anarrow area in which they can cause great damage. They usu-

3

Figure 5. Location of the study area

Figure 6. Dividing cells in the study area (250*250m) (İnce, 2005)

Fig. 5.Location of the study area.

3

Figure 5. Location of the study area

Figure 6. Dividing cells in the study area (250*250m) (İnce, 2005)

Fig. 6.Dividing cells in the study area (250× 250 m) (Ince, 2005).

ally occur on mid-ocean ridges and along transform faults,whereas mid- and deep-focus earthquakes occur along dissi-pation zones. For these shallow earthquakes, the accelerationvalues were acquired using the attenuation relations deter-mined by Boore et al. (1997), Campbell (1997), and Sadighet al. (1997), to calculate the horizontal peak acceleration,and then the average of these three values was used.

3.3.1 Attenuation relationships developed by Boore etal. (1997)

Since first publishing their attenuation relationships in 1981,Boore et al. (1997), have revised their relationships manytimes. In 1997 they proposed attenuation relationships forrandom horizontal peak ground acceleration and pseudo-acceleration response spectra for shallow earthquakes inwestern North America (Boore et al., 1997). The equationsgive ground motion in terms of moment magnitude, distance,



Fig. 7.The acceleration-distance relationship which is given variousmagnitude values according to Boore et al. (1997).

and site conditions for strike-slip, reverse-slip, or unspecifiedfaulting mechanisms. Site conditions are represented by theshear velocity averaged over the upper 30 m.

The ground motion estimation equation is:

ln(Y ) = b1 + b2(M − 6) + b3(M − 6)2

+ b5 lnr + bv ln(Vs/VA) (3)

where:

r = (r2jb + h2)1/2 (4)

In this equationY = peak horizontal accelerations in g;M = moment magnitudeM ≥ 5.00; r = closest distancefrom rupture to the station in kmr ≥ 20 km; rjb = closesthorizontal distance from the station to a point in km;Vs = average shear wave velocity to a depth of 30 m (m s−1)(Table 1);b1 = b1ssfor strike-slip earthquakes,= b1RS forreverse-slip earthquakes,= b1ALL if mechanism is not spec-ified.

The coefficients are presented in Table 2. The smoothedcoefficients in the equations for predicting ground motionwere determined using a weighted, two-stage regression pro-cedure. In the first stage, the distance and site condition de-pendence were determined together with a set of amplitudefactors, one for each earthquake. In the second stage, theamplitude factors were regressed against magnitude to de-termine the magnitude dependence.

The standard deviation of the natural logarithm of theground motion is represented byσlny . The correspondingvalues ofσlny for discrete periods are given in Table 3.

3.3.2 Attenuation relationships developed byCampbell (1997)

A consistent set of empirical attenuation relationships is pre-sented to predict the free-field horizontal and vertical com-ponents of the peak ground acceleration (PGA), peak groundvelocity (PGV), and 5 % damped pseudo-absolute acceler-

Fig. 8. The acceleration–distance relationship which is given vari-ous magnitude values according to Campbell (1997).

Table 2.Recommended values for the average shear wave velocity.

NEHRP Site Class B 1070 m s−1

NEHRP Site Class C 520 m s−1

NEHRP Site Class D 250 m s−1

Rock 620 m s−1

Soil 310 m s−1

ation response spectra (PSA). The relationships were de-rived from attenuation relationships previously developed byCampbell from 1990 to 1994. The relationships were com-bined in such a way as to emphasize the strengths and min-imize the weaknesses of each. The new attenuation relation-ships are considered to be appropriate to predict the free-fieldamplitudes of horizontal and vertical components of strongground motion from worldwide earthquakes of moment mag-nitude (M) greater than or equal to 5 and sites with distancesto seismogenic rupture (Rseis) less than or equal to 60 kmin active tectonic regions. For the estimation of PGA valuesCampbell (1997) uses the following expression:

Equations:

In(AH ) = −3.512+ 0.904M

− 1.328ln[sqrt{R2SEIS+ [0.149exp(0.647M)]2}]

+ [1.125− 0.112ln(RSEIS) − 0.0957M]F

+ [0.44− 0.171ln(RSEISj ]SSR

+ [0.405− 0.222ln(RSEIS)JSSR+ ε, (5)

whereAH is the mean horizontal component of peak groundacceleration in g;ε is the random error term with mean ofzero and a standard deviation equal to the standard error ofthe estimate of ln(AH). The standard error of estimate ofln(AH) is calculated as follows:



Table 3.Smoothed coefficients for Boore et al. (1997) PGA and SA attenuation relationship.

Period b1SS b1RS b1ALL b2 b3 b5 bv Va h σlny

PGA −0.313 −0.117 −0.242 0.527 0.000 −0.778 −0.371 1396 5.57 0.5200.10 1.006 1.087 1.059 0.753−0.226 −0.934 −0.212 1112 6.27 0.4790.11 1.072 1.164 1.130 0.732−0.230 −0.937 −0.211 1291 6.65 0.4810.12 1.109 1.215 1.174 0.721−0.233 −0.939 −0.215 1452 6.91 0.4850.13 1.128 1.246 1.200 0.711−0.233 −0.939 −0.221 1596 7.08 0.4860.14 1.135 1.261 1.208 0.707−0.230 −0.938 −0.228 1718 7.18 0.4890.15 1.128 1.264 1.204 0.702−0.228 −0.937 −0.238 1820 7.23 0.4920.16 1.112 1.257 1.192 0.702−0.226 −0.935 −0.248 1910 7.24 0.4950.17 1.090 1.242 1.173 0.702−0.210 −0.933 −0.258 1977 7.21 0.4970.18 1.063 1.222 1.151 0.705−0.216 −0.930 −0.270 2037 7.16 0.4990.19 1.032 1.198 1.122 0.709−0.212 −0.927 −0.281 2080 7.10 0.5010.20 0.999 1.170 1.089 0.711−0.207 −0.924 −0.292 2118 7.02 0.5020.22 0.925 1.104 1.019 0.702−0.198 −0.918 −0.315 2158 6.83 0.5080.24 0.847 1.033 0.941 0.732−0.189 −0.912 −0.338 2178 6.62 0.5110.26 0.764 0.958 0.861 0.744−0.180 −0.906 −0.360 2173 6.39 0.5140.28 0.681 0.881 0.780 0.758−0.168 −0.899 −0.381 2158 6.17 0.5180.30 0.598 0.803 0.700. 0.769−0.161 −0.893 −0.401 2133 5.94 0.5220.32 0.518 0.725 0.619 0.783−0.152 −0.888 −0.420 2104 5.72 0.5250.34 0.439 0.648 0.540 0.794−0.143 −0.882 −0.438 2070 5.50 0.5300.36 0.361 0.570 0.462 0.806−0.136 −0.877 −0.456 2032 5.30 0.5320.38 0.286 0.495 0.385 0.820−0.127 −0.872 −0.472 1995 5.10 0.5360.40 0.212 0.423 0.311 0.831−0.120 −0.867 −0.487 1954 4.91 0.5380.42 0.140 0.352 0.239 0.840−0.113 −0.862 −0.502 1919 4.74 0.5420.44 0.073 0.282 0.169 0.852−0.108 −0.858 −0.516 1884 4.57 0.5450.46 0.005 0.217 0.102 0.863−0.101 −0.854 −0.529 1849 4.41 0.5490.48 −0.058 0.151 0.036 0.873 −0.097 −0.850 −0.541 1816 4.26 0.5510.50 −0.122 0.087 −0.025 0.884 −0.090 −0.846 −0.553 1782 4.13 0.5560.55 −0.268 −0.063 −0.176 0.907 −0.078 −0.837 −0.579 1710 3.82 0.5620.60 −0.401 −0.203 −0.314 0.928 −0.069 −0.830 −0.602 1644 3.57 0.5690.65 −0.523 −0.331 −0.440 0.946 −0.060 −0.823 −0.622 1592 3.36 0.5750.70 −0.634 −0.452 −0.555 0.962 −0.053 −0.818 −0.639 1545 3.20 0.5820.75 −0.737 −0.562 −0.661 0.979 −0.046 −0.813 −0.653 1507 3.07 0.5870.80 −0.829 −0.666 −0.760 0.992 −0.041 −0.809 −0.666 1476 2.98 0.5930.85 −0.915 −0.761 −0.851 1.006 −0.037 −0.805 −0.676 1452 2.92 0.5980.90 −0.993 −0.848 −0.933 1.018 −0.035 −0.802 −0.685 1432 2.89 0.6040.95 −1.066 −0.932 −1.010 1.027 −0.032 −0.800 −0.692 1416 2.88 0.6091.00 −1.133 −1.009 −1.080 1.036 −0.032 −0.798 −0.698 1406 2.90 0.6131.10 −1.249 −1.145 −1.208 1.052 −0.030 −0.795 −0.706 1396 2.99 0.6221.20 −1.345 −1.265 −1.315 1.064 −0.032 −0.794 −0.710 1400 3.14 0.6291.30 −1.428 −1.370 −1.407 1.073 −0.035 −0.793 −0.711 1416 3.36 0.6371.40 −1.495 −1.460 −1.483 1.080 −0.039 −0.794 −0.709 1442 3.62 0.6431.50 −1.552 −1.538 −1.550 1.085 −0.044 −0.796 −0.704 1479 3.92 0.6491.60 −1.598 −1.608 −1.605 1.087 −0.051 −0.798 −0.697 1524 4.26 0.6541.70 −1.634 −1.668 −1.652 1.089 −0.058 −0.801 −0.689 1581 4.62 0.6601.80 −1.663 −1.718 −1.689 1.087 −0.067 −0.804 −0.679 1644 5.01 0.6641.90 −1.685 −1.763 −1.720 1.087 −0.074 −0.808 −0.667 1714 5.42 0.6692.00 −1.699 −1.801 −1.743 1.085 −0.085 −0.812 −0.655 1795 5.85 0.672

WhenAH < 0.068 g, thenσ = 0.55; when 0.068≤ AH ≤

0.21 g, thenσ = 0.173− 0.140 ln (AH); whenAH > 0.21 g,thenσ = 0.39.

The relationship ofσ to M is given by the expression:WhenM < 7.4, thenσ = 0.889− 0.069M; whenM ≥ 7.4,thenσ = 0.38.

M is the moment magnitude;RSEIS is the closest distanceto the seismogenic rupture surface;F is the style of faultingfactor (0 for strike-slip, 1 otherwise);SSR is the soft rock sitefactor (1 for soft rock, 0 otherwise);SHR is the hard rocksite factor (1 for hard rock, 0 otherwise);SSR = SHR = 0 foralluvial sites.

ln(SAH) = In(AH) + c1

+ c2 tanh[C3(M − 4.7)] + (c4 + c5M)RSEIS

+ 0.5c6SSR+ c6SHR

+ c7 tanh(c8D)(1− SHR) + fSA(D) + ε (6)

SAH, is the horizontal component of the 5 % dampedpseudo-absolute acceleration response spectra, in g;σ =

0.46615448.D is the depth to the basement rock;fSA(D) =

0D >= 1 km; = c6(l − SHR(1− D) + 0.5c6(l − D)SSRD <

1 km.



Fig. 9. The acceleration–distance relationship which is given vari-ous magnitude values according to Sadigh et al. (1997).

3.3.3 Attenuation relationships developed by Sadigh etal. (1997)

These relationships are based on the strong motion data pri-marily obtained from earthquakes in California. Relation-ships are presented for strike-slip and reverse faulting earth-quakes, rock and deep soil deposits, earthquakes of momentmagnitudeM = 4 to 8+, and distances up to 100 km. Thesite conditions representative of the rock attenuation modelsgiven here should be accepted as soft rock. The deep soil dataare from sites with greater than 20 m of soil over bedrock. At-tenuation relationships of horizontal Response Spectral Ac-celeration (5 % damping) are given in two separate equationsaccording to the soil conditions. The general form of equa-tion for rock sites is as follows:

ln(y) = C1 + C2M

+ C3(8.5− M)2.5+ C4 ln(rrup

+ exp(C5 + C6M)) + C7 ln(rrup+ 2), (7)

wherey is PGA or SA (in g), represented by the geometricmean of the two horizontal components;M is the momentmagnitude;r is the minimum distance to the rupture surfacein km; rup C2 = 1.0 for M <= 6.5; C2 = 1.1 for M < 6.5;C5 = 1.29649 forM <= 6.5; C5 = −0.48451 forM > 6.5;C6 = 0.25 forM <= 6.5;C6 = 0.524 forM > 6.5.

Note that relationships for reverse/thrust faulting are ob-tained by multiplying these strike-slip amplitudes by 1.2.

For deep soil sites (greater than 20 m of soil over bedrock):

ln(y) = C1 + C2M − C3 ln(rrup+ C4exp(C5M))

+ C6 + C7(8.5− M)2.5 (8)

C1 = −2.17 for strike-slip;−1.92 for reverse and thrustearthquakesC2 = 1.0; C3 = 1.70; C4 = 2.1863, C5 =0.32for M <= 6.5;C4 = 0.3825,C5 = 0.5882 forM > 6.5.

Fig. 10.PGA contour map for a 10 % probability of exceedance in50 yr for the Historical Penninsula of Istanbul (Poissonian model)(Ince, 2005).

Fig. 11.The PGA contour map for a 40 % probability of exceedancein 50 yr for the historical.

For spectral acceleration

The attention relations from Boore et al. (1997) and Sadighet al. (1997) were used to calculate theSs andS1 spectralacceleration parameters, and the average of these two valueswas taken as the spectral acceleration parameter.

3.4 The software

Today, the current methodology accumulation and computersoftware packages for example: NEQRISK (Lee and Tri-funac, 1985); FRISK (McGuire, 2001); SEISRISK III (Ben-der and Perkins, 1987); STASHA (Kiremidjian et al., 1992),CRISIS2001 (Ordaz, 2001); and USGS applications (Frankelet al., 1996) are used in the analysis of seismic hazard. TheSEISRISK III application was used to calculate the proba-bilistic seismic hazard of the area consisting of the districtsof Fatih and Eminonu. This software is designed to calcu-late the largest ground motion account in each node in a



Table 4.Coefficients of the horizontal response spectral accelerations (5 % damping) for rock sites.

period c1 c2 c3 c4 c5 c6 c7 c8

0 −3.15 0 0 0 0.015 −0.0009950.05 0.05 0 0 −0.0011 0.000055 0.2 0 0

0.075 0.27 0 0 −0.0024 0.000095 0.22 0 00.1 0.48 0 0 −0.0024 0.000007 0.14 0 0

0.12 0.576 0 0 −0.00184 −0.0001038 0.076 0 00.15 0.72 0 0 −0.001 −0.00027 −0.02 0 00.17 0.748 0 0 −0.00016 −0.000374 −0.084 0 00.2 0.79 0 0 0.0011 −0.00053 −0.18 0 0

0.24 0.774 0 0 0.00302 −0.000682 −0.356 0 00.3 0.77 0 0 0.0035 −0.00072 −0.4 0 00.5 −0.28 0.74 0.66 0.0068 −0.001 −0.42 0.25 0.62

0.75 −1.08 1.23 0.66 0.0077 −0.001 −0.44 0.37 0.621 −1.79 1.59 0.66 0.0085 −0.001 −0.38 0.57 0.62

1.5 −2.65 1.98 0.66 0.0094 −0.001 −0.32 0.72 0.622 −3.28 2.23 0.66 0.01 −0.001 −0.36 0.83 0.623 −4.07 2.39 0.66 0.0108 −0.001 −0.22 0.86 0.624 −4.26 2.03 0.66 0.0112 −0.001 −0.3 1.05 0.62

Table 5. Coefficients of the horizontal response spectral accelera-tions (5 % damping) for rock sites.

Pd (s) c1 c3 c4 c7

0 −1.274 0 −2.1 00.05 −0.74 0.006 −2.128 −0.082

0.075 −0.5145 0.006 −2.131 −0.07450.1 −0.375 0.006 −2.148 −0.041

0.12 −0.302 0.005 −2.162 −0.0140.15 −0.365 0.002 −2.13 00.17 −0.411 0 −2.11 00.2 −0.497 −0.004 −2.08 0

0.24 −0.59 −0.011 −2.053 00.3 −0.707 −0.017 −2.028 00.4 −0.948 −0.028 −1.99 00.5 −1.238 −0.04 −1.945 0

0.75 −1.858 −0.05 −1.865 01 −2.355 −0.055 −1.8 0

1.5 −3.057 −0.065 −1.725 02 −3.595 −0.07 −1.67 03 −4.35 −0.08 −1.61 04 −4.88 −0.1 −1.57 05 −5.364 −0.1 −1.54 0

7.5 −6.18 −0.11 −1.51 0

two-dimensional point of the grid system for a specific non-exceedance probability and time period. The seismic zonesand the coordinates of the area defined in the program andthe earthquake parameters for each zone are created. Thenthe magnitude–frequency interrelation is obtained using theGutenberg–Richter recurrence relationship (1944). In orderto determine the seismic hazards in each zone in the area,suitable attenuation relationships are used and according to

Fig. 12. SA (T = 0.2 s) contour for a 10 % probability of ex-ceedance in 50 yr for the Historical Penninsula of Istanbul (Pois-sonian model) (Ince, 2005).

the time independent Poisson model, the ground motion in-tensity can be determined with the desired probability of ex-ceedance with the probabilistic assessment. The ground mo-tion can be defined with peak acceleration and spectral ac-celeration.

3.5 Seismic hazard maps

The earthquakes with the highest risk that may occur dur-ing the average lifetime of a structure must be taken intoaccount in determining the effects of earthquakes on build-ings. It is generally accepted that an earthquake with a 10 %exceedance probability during the 50 yr lifetime of a build-ing might occur within a period of 475 yr. This is regardedas a sufficient criterion for the design of normal structures.



Fig. 13. SA (T = 1.0 s) contour map for a 10 % probability of ex-ceedance in 50 yr for the historical penninsula of Istanbul (Poisso-nian model) (Ince, 2005).

Fig. 14. SA (T = 0.2 s) contour for a 40 % probability of ex-ceedance in 50 yr for for the historical penninsula of Istanbul (Pois-sonian model) (Ince, 2005).

Depending on the sensitivity of the study area in terms ofseismic hazard, it is thought that an earthquake with a 40 %exceedance probability in a period of 98 yr should be consid-ered as an area with a higher risk. In this study, calculationswith a 10 % and 40 % exceedance probability were made fora 50-yr lifetime of a structure.

Spectral acceleration (Ss) in short periods and spectralacceleration parameters in periods of one second are de-fined in order to take into account the expected severity ofground shaking and the effects of ground layers on non-linearbehaviour related to the earthquake. The peak accelerationvalue, which is the highest value in the acceleration-timerecord, is taken into account as another parameter. The peakacceleration and spectral acceleration parameters belongingto the bedrock were obtained from the earthquake hazardanalysis. The bedrock peak acceleration values calculated ac-cording to a 10 % exceedance probability in 50 yr are given

Fig. 15. SA (T = 1.0 s) contour for a 40 % probability of ex-ceedance in 50 yr for for the historical penninsula of Istanbul (Pois-sonian model) (Ince, 2005).

Fig. 10. The bedrock peak acceleration values calculated ac-cording to a 40 % exceedance probability in 50 yr are givenFig. 11. The spectral acceleration parametersSs andS1 calcu-lated according to a 10 % exceedance probability in 50 yr areshown in Figs. 12 and 13. The spectral acceleration param-etersSs andS1 calculated according to a 40 % exceedanceprobability in 50 yr are shown in Figs. 14 and 15.

3.6 Earthquake motion simulation

Artificial earthquake records compatible with design be-haviour spectrum must be produced after determining theacceleration parameters of earthquake ground motion. Toachieve this, analytical approaches, Green’s analytical func-tions, stochastic simulation, or hybrid methods can be used.The filter parameters to be applied are determined eitherto make the calculated ground motion features compatiblewith Fourier amplitude spectrums determined with empiri-cal methods or to be compatible with some theoretical spec-trums. The filter parameters to be applied are also determinedaccording to the regional earthquake source, features of wavepropagation medium, and local ground conditions if they ex-ist. FINSIM (Beresnev and Atkinson, 1997) and TARSCHTS(Deodatis, 1996; Papageorgiou et al., 2000) are stochasticmethods produced to simulate the earthquake motion. In theFINSIM stochastic method, the fault plane is considered tooccur from the low fault plane. Each part of a fault is con-sidered as a point source, and the propagation from each iscalculated with Boore’s (1983) method. In this method, therupture is considered to start from the centre and spread alongthe fault plane at a constant speed. The lower fault particleswhich the rupture reaches join the wave propagation one af-ter another. The ground movement at the observation point iscalculated by adding the waves from each sub-fault.

TARSCHTS was developed by Deodatis (1996) to ac-quire the ground motion at the time medium compatible



Fig. 16. Synthetic earthquake record obtained by TARSCHTS forthe A18 cell (Ince, 2005).

with behaviour spectrum. Papageorgiou et al. (2000) cre-ated a computer simulation program that creates artificialacceleration-time records for ground movement compatiblewith the desired acceleration spectrum. The simulation at thetime medium are unstable and random phased.

The TARSCHTS application was used to produce groundmotion simulations in this study, and artificial records wereproduced on the basis of a total of 307 cells measuring250× 250 m in the study area. The compatibility of the be-haviour spectrum of the acceleration-time record acquiredby the TARSCHTS application with the NEHRP behaviourspectrum and the acquired acceleration-time record for asample cell are shown in Figs. 16 and 17.

4 Conclusions

The bedrock of the region of a 10 % exceedance probabilitycalculated according to the peak acceleration values rangedfrom 0.30 g to 0.40 g; the 40 % exceedance probability calcu-lated according to the acceleration values ranged from 0.17 gto 0.22 g. TheSs 10 % exceedance probability calculated ac-cording to the spectral acceleration parameter ranged from0.67 g–0.85 g;S1 is a spectral acceleration parameter variedbetween 0.22 g–0.28 g. TheSs 40 % exceedance probabilitycalculated according to the spectral range was from 0.46 gto 0.38 g acceleration parameter;S1 is a spectral accelerationparameter varied from 0.12 g to 0.14 g.

According to the Turkish seismic design code the designacceleration value for first-degree earthquake zone of Turkeyis defined as 0.40 g. In this study, the bedrock peak accelera-tion value reaches 0.40 g according to a 10 % probability ofexceedance. In cases where there are thick soil layers overbedrock, the earthquake wave will undergo ground amplifi-cation until it reaches the ground surface especially in softclay layers and fill, which results in a surface peak groundacceleration value much higher than 0.40 g. Therefore, it isrecommended that a more realistic acceleration value be de-

Fig. 17. Comparison of the syntetic response spectrum obtainedfrom TARSCHTS and NEHRP response spectrum for the A18 cell(Ince, 2005).

fined for the seismic design code in Turkey, taking into ac-count the different ground conditions.

Acknowledgements.The author would like to thank I. KutayOzaydın, Mustafa Yıldırım and Pelin TohumcuOzener.

Edited by: M. E. ContadakisReviewed by: D. Papanastassiou and one anonymous referee

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