AN INTEGRATED STUDY USING MODIFIED MERCALLI INTENSITY AND PEAK AMPLITUDES FROM INITIAL P ARRIVALS FOR EARTHQUAKE EARLYWARNING SYSTEMS

Abstract

Present study is an attempt to discover new parameters for application to Earthquake Early Warning System for issuance of warning alarm at user sites. In this study two different parameters were analyzed to quickly assess earthquakes by using early arrivals of seismic signals to speculate damaging ground shaking. This integrated work is divided into two parts, the first part caters to the prediction of damaging ground shaking using the initial 2 second records of P wave. We observed a relationship between the calculated modified mercalli intensity (obtained using initial 2 seconds record of P wave) and magnitude hence a threshold value for intensity can be determined to issue warning for potentially damaging earthquakes ( magnitude greater than 5.5). It considers modified Destructive Intensity approach of UrEDAS of Japan. For the later part the main focus has been on developing empirical relationships between vertical peak ground acceleration and epicentral distance with a new averaging approach for different magnitudes within range of 4.0-7.0. This relationship was used to approximate the decay of vertical peak ground acceleration as the epicentral distance increases. We also observed that logarithm of vertical peak ground acceleration and horizontal peak ground acceleration obtained within 80 kms of epicentral distance range show strongly positive relationship. For this part we assume that current methodologies that are being employed in Earthquake Warning Systems will provide us with an initial estimate of event size within few seconds of P phase detection, with a permissible value of uncertainty. With an initial estimate of event size using early P or S wave signals accompanied by attenuation relationships between vertical peak ground acceleration and epicentral distance can aid in deducing the Kilometer range upto which warning should be given so as to escape false alarm. The data for estimating these parameters and deriving the relationships was taken from strong motion accelerograms recorded by borehole stations from the Kiban Kyoshin network for Japanese earthquakes ( KiK-net seismic array,Japan). The training dataset consisted of 125 shallow source earthquake records with a magnitude range(Mw) 4.0-7.0 within the epicentral distance range of 80 kms. The test data from the same source consisted of 80 earthquake records. The calculated horizontal and vertical peak ground acceleration values using the attenuation relationships for different magnitudes were validated on test dataset of same magnitude range and epicentral distance range. The results show good correlation between observed and calculated values.