عنوان مقاله [English]
In this study, new empirical relationships to estimate key parameters in Earthquake Early Warning (EEW) system including magnitude, epicentral distance and Peak Ground Acceleration (PGA) are introduced based on features of the initial portion of P-wave’s amplitude envelope curve.
For this purpose, 226 time series recorded by bore-hole accelerometers of Japanese KiK-net are processed for 3 and 7.2 M_JMA magnitude events and epicentral distances of less than 50 km. Hereby, an improved single station method for estimation of epicentral distance and two new methods for estimation of magnitude and amplitude of PGA are proposed based on exponentially envelope curve as B×t×e^(-A×t) in known B-∆ method. First, a scaling relationship of B×T_r-∆ is proposed to estimate epicentral distance in which is well correlated for larger earthquakes (M>6), that shows more robust and reliable results rather than the previous method(B-∆). Non-dimensional parameter, T_r depends on earthquake magnitude and A parameter in the above mentioned function. By using the features of acceleration envelope curve and peak amplitude of P-waves, scale parameter S_a is proposed which is well correlated with magnitude and has capability of estimating magnitude with standard deviation of less than ±0.77 magnitude unit. S_a is proportional to a part of area under envelope curve as a function of magnitude. Moreover, it is indicated that PGA in a single station can be estimated by using envelope curve characteristics of initial P-waves portion.
EEW systems are established in order to reduce human and financial losses caused by destructive earthquakes. Nowadays, an efficient EEW system should be capable of timely and correctly recognition of an earthquake, precise magnitude, epicentral distance and amplitude of strong ground motions estimation in areas around fault zones and areas distant from the earthquake epicenter, and issuing warning whenever the earthquake can be destructive. In recent decades, with development of global and local networks, and modern methods for data processing and collecting information from real-time processing, EEW systems have been significantly promoted throughout the world and in some countries have been implemented with high seismicity potential such as Japan (Nakamura 1988, 2004; Kamigaichi 2004; Kamigaichi et al. 2009; Horiuchi et al. 2005; Hoshiba et al. 2011), Mexico (Espinosa-Aranda et al. 1995, 2009) and Taiwan (Wu and Teng 2002; Wu and Zhao 2006).
In general, there are two types of EEW systems: regional early warning systems and the on-site ones. In the first case, a network of seismometers and accelerometers are installed near fault zones to receive the seismic wave phases, that these fault areas are located away from the target areas. Upon the occurrence of an earthquake, seismic source parameters (including magnitude and location of the earthquake) from the recorded initial portion of P-waves are evaluated at least in 3 or 4 stations, then, the earthquake intensity in target points is estimated by using the attenuation relations (Satriano et al. 2010; Kuyuk and Allen 2014).