Site Effect and its Relationship to the Intensity and Damage Observed in the June 27, 1998 Adana-Ceyhan Earthquake

Abstract

The site response at 15 stations in the Adana-Ceyhan region (Southern Turkey) is calculated from the recordings of aftershocks of June 27, 1998 Adana-Ceyhan earthquake (M S ¼ 6.2) by using the Standard Spectral Ratio (SSR) and the Horizontal-to-Vertical Spectral Ratio (HVSR) methods. While the two methods are in good harmony at a few stations in determining the site effects, they show differences on the estimated amplifications or on the site resonance frequencies at most stations. It was not clear which one of the two methods underestimates or overestimates the amplification values. We observe that at some stations, where the local site conditions are rather complex, the vertical component records are strongly influenced from the local soil conditions. Thus, the HVSR method fails at these stations. The SSR method underestimates the amplifications at some stations since the rock site, selected as reference site, has its own site response and/or the path correction we applied, considering the geometrical spreading factor only, is insufficient. At the sites where high intensity values were observed, we found high amplifications. The fundamental soil frequencies characterize the damage properties observed in the Adana-Ceyhan earthquake. The fundamental soil frequency is nearly at 1.1 Hz at the Ceyhan site, where severe damage was observed in the 5-6 story buildings, while the fundamental soil frequency is between 3-6 Hz at the Adana site, where damage was in the low-story buildings. Therefore, in addition to inefficient construction practices, it is clear that the resonance effects have also contributed to the observed damage.

Stochastic finite-fault modeling of ground motions from the June 27, 1998 Adana-Ceyhan earthquake

“…For the local response, the mean soil and rock amplification functions is used. Yalcinkaya and Alptekin (2005a) estimated site-specific amplification functions from the weakmotion recordings at 15 stations located in the AdanaCeyhan region. It is considered that the geologic characteristics underlying their stations display similarities with those of our stations, because all stations are located in the same tectonic area, albeit even if their locations are different.…”

“…Even if the discussions about the accuracy of results of the Horizontalto-Vertical Spectral Ratio method continue; that is, it usually underestimates true amplifications (e.g. Yalcinkaya and Alptekin, 2005a), we were forced to use the results of this method for the mean rock amplification function, because it was impossible to define the best rock station for reference. The mean soil and rock amplification functions and their standard deviations derived for this study are presented in Fig.…”

“…The stations at similar epicentral distances recorded very different peak accelerations depending on local site condition and rupture directivity. Site response analyses based on spectral ratios revealed that soil behavior was one of the most significant factors in the damage to buildings caused by the earthquake (Celebi, 2000;Yalcinkaya and Alptekin, 2005a). Simulation of ground motions using a stochastic finite-fault model- G o k s u n F a u l t Z o n e M i s i s -C e y h a n F a u l t K o z a n F a u l t June27, 1998 Adana-Ceyhan Earthquake A m a n o s F a u l t E a s t A n a t o l i a n F a u l t Z o n e Y u m u r t a l k F a u l t ing technique will help to better understand this earthquake and its effects on structures and buildings.…”

Urban Geology, Earthquake and Planning by Means of GIS for Development Needs, A Case Study, Iran

“…Recent destructive earthquakes have shown evidences of the effects of surface and subsurface geology and topography on ground motion characteristics at a given site. Among these effects we have: amplification and attenuation patterns, strong spatial variability of amplification and polarization with in a small area [1, 2,3]. Several earthquakes such as the 1985 Michoacan (Mexico), 1988 Spitak (Armenia), 1990, and 2003 Bam (Iran) earthquakes have clearly demonstrated that local soil and sediment conditions (site effect or site specific condition) can have a significant influence on the ground motion and damage pattern, respectively [1, 2,4].…”

“…Among these effects we have: amplification and attenuation patterns, strong spatial variability of amplification and polarization with in a small area [1, 2,3]. Several earthquakes such as the 1985 Michoacan (Mexico), 1988 Spitak (Armenia), 1990, and 2003 Bam (Iran) earthquakes have clearly demonstrated that local soil and sediment conditions (site effect or site specific condition) can have a significant influence on the ground motion and damage pattern, respectively [1, 2,4]. In the other word, Ground shaking and its associated damage to engineered structures can be strongly influenced, not only by source and path effects, but also by surface and sub-surface geological (depth and type of bedrock, underground sediments) and geomorphologic conditions in the vicinity, known as "local site effects".…”