Observation of topographic site effects in Israel

We explore the feasibility of using earthquake, explosion, and microtremor records in estimating topographic site effects in Israel. Predominant frequency and amplification factors were determined for the high plateau on the western cliff of Timna (Mt. Berech), Mt. Atzmon, Mt. Meron, and Mt. Massada. Ground motion amplification was determined by implementing three spectral ratio techniques: (1) conventional spectral ratio with respect to a reference site; (2) spectral ratio of the horizontal-to-vertical components of earthquake shear-waves observed simultaneously at the site (receiver function); and (3) horizontal-to-vertical spectral ratio of microtremors (Nakamura estimates). The investigated sites exhibit amplification which can be attributed to the topography. At Mt. Atzmon, within the 1.3-2.0 Hz range, the amplification is of the order of factor 4. At Mt. Berech amplification levels of 3.0-3.5 are observed in the frequency range 1.5-4.0 Hz. Mt. Meron exhibits a relatively strong amplification effect (up to 4) in the frequency range 2.5-3.5 Hz. Amplification (up to 3.5) around 1.4 Hz is observed at MSD. We found that the three techniques were successful in identifying topographical site effects. The Nakamura method, however, could not be used to identify higher modes of resonant frequencies. These methods may be used in the seismic hazard assessment process for ridges and mountain tops, sites for prospective settlements, communication relay stations, bridges, rope-drive, and power transmission towers.