Eser Durukal

Strong Ground Motion

The availability of empirical strong ground motion data will always be less that what would be needed to meet the needs of a variety of ever demanding engineering problems. A set of strong ground motions, either recorded or theoretically simulated, is the necessary database for the civil engineering design, regarding both new construction and performance assessment of the existing built environment. The future of performance based earthquake resistant design and sophisticated non-linear dynamic analysis will rely on the development of analytical tools that can simulate realistic ground motions in terms of tectonic structure, earthquake physics, local geological and geotechnical conditions. This need is more acute for large magnitude earthquakes in near-field conditions. The state-of-the art and success in strong ground motion simulation is developing at a fast rate and we all hope that it meets the demand in foreseeable future.

Dynamic Response of Two Historical Monuments in Istanbul Deduced from the Recordings of Kocaeli and Düzce Earthquakes

Strong-motion networks installed in the Hagia Sophia Museum and in the Suleymaniye Mosque in Istanbul, Turkey, recorded a series of events during the 17 August 1999, Kocaeli ( M w 7.4) and 12 November 1999, Duzce, Turkey ( M w 7.2) earthquakes and during the following aftershock activity. The time-domain and frequency-domain analysis of data presented in this article yielded the following results: On the basis of the pre-1999 recordings in Hagia Sophia it was observed that the modal frequencies tend to change with amplitude and duration of shaking. This observation is supported by the recent data as well. Local problems were noted in Hagia Sophia in the southwest main pier and possibly in Suleymaniye in the west main arch. Significant vertical vibrations at the crowns of the east and west main arches in Hagia Sophia are probably indicating locations where most of the damage is to be expected during a major earthquake close to Istanbul. A postearthquake, quick ambient vibration survey conducted in Hagia Sophia showed a frequency drop in the first two modal vibrational frequencies on the order of 4%–5%, indicating the need for a comprehensive ambient vibration study. Modal shapes and first-order estimates of modal damping of the two structures have also been assessed.

ML Scale in Northwestern Turkey from 1999 Izmit Aftershocks: Updates

We present an update of the local magnitude scale previously calibrated for northwestern Turkey by Baumbach et al. (2003). The path coverage in the westernmost part of the analyzed area has been increased, as well as the number of amplitudes for distance greater than 110 km. Furthermore, a set of recordings from accelerometric stations operated by the Kandilli Observatory and Earthquake Research Institute (koeri) has been merged with the recordings by the Sapanca-Bolu and German Task Force seismological networks. In all, 4047 recordings from 528 earthquakes recorded by 31 seismometers and 23 accelerometers are considered to calibrate the local magnitude scale over a hypocentral distance range from 10 to 190 km. By analyzing the unit covariance matrix and the resolution matrix, we show how the source-to-station geometries of the seismic and strong-motion networks affect the uncertainties of the computed station corrections, attenuation coefficients, and magnitudes. The assumptions made concerning the reference station correction, and the change in the amplification for the Wood–Anderson torsion seismograph from 2800 to 2080 (Uhrhammer and Collins, 1990) introduced an offset of about 0.34 in the magnitudes with respect to Baumbach et al. (2003), with the updated local magnitude scale ranges from 0.50 to 5.91. The distribution of the residuals with distance confirms that the extension of both the magnitude and distance ranges and the improved path coverage have preserved the high quality that characterized the data set analyzed by Baumbach et al. (2003).

Source Parameters and Seismic Moment–Magnitude Scaling for Northwestern Turkey

The source parameters of 523 aftershocks (0.5 M L ω -square model multiplied by an exponential term of frequency. The latter term is introduced to estimate the high-frequency ( f > 12 Hz) fall-off of the acceleration source spectra by computing the κ parameter. The seismic moments obtained range between 1.05 × 10 14 and 2.41 × 10 17 N m, whereas the Brune stress drops are between 0.002 and 40 MPa. The κ value varies between 0.00 and 0.08 sec, indicating a decay of the acceleration level at the higher frequency part of the spectrum greater than that assumed by the ω −2 model. Both the stress drop and the κ parameter show the tendency of increasing with aftershock magnitude. No evidence of self-similarity breakdown is observed between the source radius and M 0 . Finally, both the seismic moment and the moment magnitude are compared with the local magnitude to derive new moment–magnitude relationships for the area.

Effectiveness of Hybrid Green’s Function Method in the Simulation of Near-Field Strong Motion: An Application to the 2004 Parkfield Earthquake

This study discusses the effectiveness of the hybrid Green’s function method (hgf) in simulating near-field strong ground motions. The hgf method starts with calculating the synthetic Green’s function, which is a combination of deterministically calculated, low-frequency motion and stochastically simulated, high- frequency motion. Summation of Green’s functions using the numerical framework of the empirical Green’s function method gives the large earthquake synthetics. We simulated the M 6.0 2004 Parkfield earthquake producing near-fault ground motion that favorably compares with the empirical data. We carried out simulations for the frequency range 0.1–25 Hz at eight rock and four soil site stations. Frequency- dependent site-amplification values are calculated using empirical data and considered for the soil site simulations. The comparisons of simulated motion in time and frequency domain proved the efficiency of the hgf method in such broadband simulations.

Investigation of the Rail-Induced Vibrations on a Masonry Historical Building

Increasingly historic masonry buildings are subjected to higher levels of traffic and rail vibrations due to urbanization and population growth. Deterioration and destabilisation of these buildings may result, especially if they were previously damaged (e.g. earthquakes or settlement problems). To better understand building response, vibration measurements were conducted on the Little Hagia Sophia Mosque, located adjacent to Istanbul’s Sirkeci-Halkali railway line. Transport-induced vibrations were recorded at several points on the ground and building. Attenuation characteristics in the ground and amplification features on the building were examined. Peak particle velocities often exceeded previously established thresholds for human perception and in some cases for structural damage. These are evaluated with respect to the building’s condition.

Development of Earthquake Lossmap for Europe

For almost real-time estimation of the losses after a major earthquake in the Euro-Mediterranean region, the Joint Research Area-3 (JRA-3) component of the European Union (EU) Project “Network of Research Infrastructures for European Seismology – NERIES” foresees (at several levels of sophistication): 1. Finding the most likely location of the source of the earthquake using regional seismotectonic data base; 2. estimation of the spatial distribution of selected site-specific ground motion parameters; 3. correlation/verifyication/enrichment of the estimated ground shaking information with the available on-line strong motion data; and 4. estimation of physical damage and casualty distributions. These LossMaps will provide the required vital information within minutes after an earthquake to European emergency response agencies, in a manner similar to the United States Geological Survey (USGS)s Prompt Assessment of Global Earthquakes for Response (PAGER) system. A methodology that incorporates the regional dependencies and sources of uncertainty stemming from ground motion predictions, fault finiteness, site modifications, inventory of elements subjected to the hazard, and the vulnerability relationships is under preparation with researchers from Imperial College, NORSAR and ETH-Zurich. A pilot application is established for Turkey that encompasses the gridded earthquake source, Quaternary, Tertiary, Mesozoic (QTM) geological classification and physical and demographic inventory mapping for the whole country. Within the scope of this study, loss estimations were computed for the 1999 Kocaeli earthquake using several approaches and comparisons made with observed values. The LossMap tool will be available for the first estimation of damage immediately after an earthquake in Turkey by the end of 2007 and for the whole Euro-Med region by the end of 2009.

Strong Motion Networks: A Tool For The Assessment of Earthquake Response of Historical Monuments

Strong motion networks installed in two historical monuments in Istanbul, Turkey, namely in Hagia Sophia Museum and in Suleyrnaniye Mosque, yielded valuable information regarding their time-domain and frequency-domain dynamic characteristics. The existing information was enhanced by recordings obtained during the recent August 17, 1999, Kocaeli (Mw=7.4) and November 12, 1999, Duzce, Turkey (Mw=7.2) earthquakes and during the following aftershock activity. Analysis of data yielded following results: The two buildings with similar structural support systems have different vibration characteristics. There is an earthquake specific variation of modal frequencies in the two structures which exists during low amplitude events as well. Local problems in terms of excessive vibrations exist in the southwest main pier of Hagia Sophia and possibly in the west main arch of Suleyrnaniye. Significant vertical vibrations at the crowns of the east and west main arches in Hagia Sophia are probably indicating locations where most of the damage are to be expected during a major earthquake close to Istanbul. The strong motion accelerometer networks are valuable tools for monitoring of historical structures and help to identify potential problems and/or to explain past/present structural problems. It is expected that such networks will become a standard tool for investigations towards the preservation of historical buildings in seismic areas in the future.

Seismic Assessment and Rehabilitation of Historical Unreinforced Masonry (URM) Buildings in Istanbul

The aim of the study is to evaluate the earthquake performance of two historical buildings located in Istanbul exposed to a M+7 earthquake expected to hit the city and, to propose solutions for their structural rehabilitation and/or strengthening. Both of the buildings are unreinforced clay brick masonry (URM) structures built in 1869 and 1885, respectively. The first building is a rectangular-shaped structure rising on four normal floors and the second one has an L shape with one basement floor and three normal stories. They survived the 1894, Ms7.0 Istanbul earthquake, during which widespread damage to URM buildings took place in the city [3]. No information could be reached whether and in what way they were affected by this earthquake. Although, there can be seen some cracks on some perimeter as well as secondary walls of the buildings. Determination of the site-specific performance assessment and retrofit design basis earthquake ground motion is achieved through deterministic seismic hazard assessment. The buildings are modeled and analyzed as a three-dimensional assembly of finite elements using SAP2000 v11 (Static and Dynamic Finite Element Analysis of Structures) [8] software package. The linear dynamic analysis procedure of FEMA 356 and ASCE41-06 [1, 2] is followed for the seismic assessment of the buildings. In order to improve earthquake resistance of the buildings, reinforced cement jacketing of the main load-carrying walls and application of fiber reinforced polymer (FRP) bands to the secondary walls are proposed.

Strong-Motion Data Acquisition, Processing and Utilization with Applications to Istanbul Strong Motion Network

The strong ground motion network operated by Bogazici University in and around Istanbul has been described, including the rapid response and early warning system, structural instrumentation, instrument calibration and, processing, availability and utilization of the data.