Seismic Risk Assessment of Architectural Heritages in Gyeongju
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EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Nat. Hazards Earth Syst. Sci., 13, 251–262, 2013 Natural Hazards Natural Hazards www.nat-hazards-earth-syst-sci.net/13/251/2013/ doi:10.5194/nhess-13-251-2013 and Earth System and Earth System © Author(s) 2013. CC Attribution 3.0 License. Sciences Sciences Discussions Open Access Open Access Atmospheric Atmospheric Chemistry Chemistry Seismic risk assessment of architectural and Physics and Physics Discussions Open Access Open Access heritages in Gyeongju considering local site effectsAtmospheric Atmospheric H.-J. Park1, D.-S. Kim1, and D.-M. Kim2 Measurement Measurement 1Department of Civil and Environmental Engineering, Korea Advanced Institute of Science andTechniques Technology (KAIST), Techniques 291 Daehak-ro, Yuseong-gu, Daejeon, Korea Discussions 2 Open Access Research Division of Architectural Heritage, National Research Institute of Cultural Heritage, Korea (NRICH), Open Access 132 Munji-ro, Yuseong-gu, Daejeon, Korea Biogeosciences Biogeosciences Correspondence to: D.-S. Kim ([email protected]) Discussions Received: 3 January 2012 – Published in Nat. Hazards Earth Syst. Sci. Discuss.: – Open Access Revised: 9 October 2012 – Accepted: 1 December 2012 – Published: 8 February 2013 Open Access Climate Climate Abstract. A seismic risk assessment is conducted for cul- Buddhist art. Gyeongju is locatedof the in a relatively Past higher earth- of the Past tural heritage sites in Gyeongju, the capital of Korea’s an- quake prone region nearby the Yangsan fault line and has his- Discussions cient Silla Kingdom. Gyeongju, home to UNESCO World torical records of frequent seismic damage. In particular, the Heritage sites, contains remarkable artifacts of Korean Bud- region’s valuable architectural heritages are exposedOpen Access to seis- Open Access dhist art. An extensive geotechnical survey including a series mic danger. A seismic risk assessment is therefore required Earth System of in situ tests is presented, providing pertinent soil profiles to prevent damage to the area’sEarth architectural System heritages. for site response analyses on thirty cultural heritage sites. It has been well documentedDynamics that local site effects may Dynamics After the shear wave velocity profiles and dynamic material substantially affect amplification of ground motion with the Discussions properties were obtained, site response analyses were car- dominant site period range, because earthquake motions at ried out at each historical site and the amplification charac- the bedrock can be drastically modified in amplitude, fre- Open Access Open Access teristics, site period, and response spectrum of the site were quency content, and durationGeoscientific during the propagation of seis- Geoscientific determined for the earthquake levels of 2400 yr and 1000 yr mic waves within soil (Aki,Instrumentation 1993; Kim et al., 2002; Pitilakis, Instrumentation return periods based on the Korean seismic hazard map. Re- 2004; Sun et al., 2005; Chavez-Garcia,Methods 2007). and In the Korean Methods and sponse spectrum and corresponding site coefficients obtained seismic design code (MOCT, 1997), local site effects are con- from site response analyses considering geologic conditions sidered according to a siteData classification Systems system and corre- Data Systems differ significantly from the current Korean seismic code. sponding site coefficients, which are similar to the 1994 and Discussions Open Access Open Access This study confirms the importance of site-specific ground 1997 NEHRP Provisions (BSSC, 1994, 1997), despite sub- Geoscientific response analyses considering local geological conditions. stantial differences in localGeoscientific geological conditions. Kim and Results are given in the form of the spatial distribution of Yoon (2005) and Lee et al. (2012) showed significant devia- Model Development Model Development bedrock depth, site period, and site amplification coefficients, tions in response spectra between soil response analyses and Discussions which are particularly valuable in the context of a seismic code-defined values. vulnerability study. This study presents the potential ampli- Rock-outcrop motions defined in the Korean seismic de- Open Access Open Access fication of hazard maps and provides primary data on the sign code correspond toHydrology seismic hazard and maps developed for Hydrology and seismic risk assessment of each cultural heritage. various return periods based on historical earthquake events based on the relation ofEarth ground motionsSystem to earthquake in- Earth System tensities. Because most of theSciences historical events were not Sciences experienced at rock outcrops but rather at the ground sur- Discussions 1 Introduction Open Access face of the soil sites and the effects of site amplificationOpen Access were already included in the historical earthquake intensi- Gyeongju, the capital of the ancient Silla Kingdom ties, the rock-outcrop motion in the hazard map is poten- Ocean Science (57 BC ∼ 935 AD), is considered the most important historic Ocean Science tially overestimated. In order to assess the extent of potential Discussions city in Korea and contains remarkable artifacts of Korean Open Access Published by Copernicus Publications on behalf of the European Geosciences Union. Open Access Solid Earth Solid Earth Discussions Open Access Open Access The Cryosphere The Cryosphere Discussions 252 H.-J. Park et al.: Seismic risk assessment of architectural heritages in Gyeongju Fig. 1. The satellite picture of Gyeongju historical areas, the location and foreground of typical cultural heritages. overestimation in the hazard map, it is essential to evaluate and cultural heritages due to the case-dependent nature of the range of site amplification at various historical sites using their seismic performance. a ground response analysis and interpret the spatial geotech- nical information, such as depth to bedrock, site period, and amplification characteristics, using a geographic information 2 Selection of test sites around Gyeongju historic areas system (GIS). In this study, site response analyses were performed at Among the many cultural heritages in Gyeongju, cultural historical sites in Gyeongju to assess seismic risk. Thirty heritage sites with historical earthquake records and other na- historical sites of cultural heritages were selected consider- tional architectural treasure sites were selected for site inves- ing importance and geographical distributions, and the repre- tigation and ground response analysis. The UNESCO World sentative shear wave velocity (Vs) profiles were determined Heritage sites selected for this study include “Seokguram by surface wave tests. One-dimensional site response anal- Grotto and Bulguksa Temple”, “Gyeongju Historic Areas”, yses were carried out at each historical site and the ampli- and “Yangdong Village”. fication characteristics, site period, and response spectrum The Gyeongju Historic Areas host outstanding examples of the site were determined. Amplification coefficients and of Korean Buddhist art including sculptures, reliefs, pagodas, the corresponding response spectra were compared with the and the remains of temples and palaces from the period of coded values and the importance of a site-specific analysis the seventh to the tenth centuries, marking the culmination of for risk assessments was demonstrated. Sixty pre-existing this form of artistic expression. There are five major belts that soil datasets were gathered in the central area around a 7 km make up the Gyeongju Historic Areas: the Mount Namsan by 7 km area encompassing Gyeongju and ground response Belt, the Wolseong Belt, the Tumuli Park Belt, the Hwangny- analyses were additionally performed. Necessary informa- ongsa Belt, and the Fortress Belt, as shown in Fig. 1. tion for seismic risk assessment such as bedrock depth, site The historical data of earthquakes in the Gyeongju area period, peak ground acceleration, and site amplification coef- are tabulated in Table 1 (NRICH, 2009). Notably, the cul- ficients was spatially interpreted for the scenario earthquakes tural heritage sites that experienced damage to structures due and the potential overestimation of rock-outcrop motion in to earthquake events include the “three storied stone pagoda a hazard map based on historical records was assessed. Seis- at Bulguksa Temple (Site No. 2–2),” “Hwangnyongsa Tem- mic microzonation becomes particular valuable in the case of ple site (Site No. 6–1),” and “Mangdeoksa Temple site (Sites assessing the seismic vulnerability of historical monuments No. 7–1 and 7–2)”. Note that mountains and rock outcrops have relatively lower possibilities of local site amplification Nat. Hazards Earth Syst. Sci., 13, 251–262, 2013 www.nat-hazards-earth-syst-sci.net/13/251/2013/ H.-J. Park et al.: Seismic risk assessment of architectural heritages in Gyeongju 253 Table 1. Historical records of seismic damage in Gyeongju. Month, Year Historical Records on the Earthquake for Gyeongju Inscribed Classification Surface Seismic Magnitude Potential Amplification Korean of Memory in Korea Geology Intensity by (in this study) Memory (NRICH, (NRICH, Inference 2009) 2009) (NRICH, 2009) Dec. 27 AD The ground shook and residences collapsed. ∼ 7–8 ∼ 5.0–6.0 ∼ 1.46–1.53 (Mean value of Gyeongju area) Jul. 89 AD The ground shook and cracked. Many people died ∼ 8–9 ∼ 5.5–6.5 ∼ 1.46–1.53 (Mean value of as residential homes