A STUDY BETWEEN THE RELATIONS OF CASPIAN SEA WAVES HEIGHT AND THE LOW FREQUENCY SEISMIC NOISE MEASUREMENT IN TEHRAN Saeed SOLTANI 1 , Ebrahim HAGHSHENAS 2 ABSTRACT The correlation of ambient noise energy at low frequency with oceanic waves height are studied in Tehran by using weighted average function for measuring oceanic wave's mean. Based on some article that published in mid-twentieth century about the correlation between microtremor and meteorological activities the authors showed that the low frequency microtremors are generated by the pressure variations on the sea floor caused by the ocean waves. These pressure variations are the result of the standing waves and their frequency is twice the frequency of the original traveling ocean waves. For Tehran (capital of Iran) with a direct distance about 80Km from Caspian Sea, based on the low attenuation of microtremor generated in seas we assumed this sea as a source for low frequency energy. Haghshenas (2005) examined the relationship between the evolution of the microtremor’s maximum spectral amplitude on the north-south component, at the low frequency at some stations in Tehran, and variations of wind speed recorded at Caspian Sea’s meteorological stations. In this article we used significant wave height (that defined as four times of the square root of the zeroth-order moment of the wave spectrum based on numerical modeling) as a source parameter because in oceanography Significant wave height is commonly used as a measure of the height of ocean waves. So, we performed the 1-week continuous recording at North of Tehran as an experiment for study about the correlation between microtremors and significant wave height. The results show that the wave heights were not the main factor that generates low frequency amplitudes in Tehran region. Keywords: Microseism; Significant wave height; HVSR; Caspian Sea 1. INTRODUCTION Classification of ambient noise sources, its stability over time and its effect on temporal variation (in frequency and amplitude) of H/V curves are important are the important challenges in site effect studies using the H/V method. Gutenberg (1958) was the first one that studied in this issue by establishing a list of the different types of noise sources according to their frequency. He showed that noise has basically two different origins (natural or cultural) based on its frequency content. These two categories of sources led researchers to distinguish between microseisms and microtremors, corresponding respectively to natural and cultural sources, and relatively low and high frequency. The terms microseisms (vibratory motion caused by the sea waves) and microtremors (cultural noise such as traffic, machinery etc.) are sometimes synonymously used for ambient noise but in literature high frequency noise signals with periods below 2sec are called “microtremors” and those above 2sec are called “microseisms” or "long-period microtremors” (Kulhanek, 1990; Yamanaka et al., 1994). Bonnefoy-claudet (2004) revealed the sensitivity of the microseism’s H/V ratio to the variations in the spectral amplitudes of the noise by the continuous recording over a long period of time (several weeks). Guillier et al (2007) confirmed this result performing the experiment on selected sites in 1 Ph.D. Candidate, IIEES, Tehran, Iran, s.soltani@iiees.ac.ir 2 Assistant Professor, IIEES, Tehran, Iran, Haghshen@iiees.ac.ir