An Effective Earthquake Monitoring Process for Emergency Response

Abstract

There is no doubt that, investigation of durability of surface ground and dynamic characteristics of structures are important steps to estimate damage that will be caused by earthquakes. Together with this, it has been widely recognized that, systematical and continuous monitoring of earthquakes is indispensable factor for early warning systems.

Japan has 10% of global seismic energy and suffers severely from earthquakes. There have been many efforts including early warning system since 1960’s. For the important infrastructures and automated systems, having an early alarm and earthquake information, even a few seconds before the destructive wave arrives, is still an important issue for many countries. Starting with conventional alarm seismometers and continuing with UrEDAS (Urgent Earthquake Detection and Alarm System), early warning system has been extensively used in Japan Railways for stopping high speed trains. This early warning system has been improved recently and this new effective real time monitoring approach is proposed in present study.

Basic concept of this system is to catch earthquake motion by P waves in and around the earthquake occurring area. For this purpose, new characteristic parameters, named as PI (P wave index) and DI (Damage Intensity) of seismic motion are proposed to be able to define destructiveness of the earthquake and effectively realize P wave alarm system. DI is defined as an inner product of acceleration and velocity vectors, at each time step. Multiplication of DI with mass received seismic motion indicate a power of motion acting to the object. With a P wave arrival, DI increases drastically and after S wave arrives it reaches to its maximum value. This value (maximum of DI) is named as DI value. PI is defined as maximum of DI calculated at the time step around P wave arrival and this value is suggested to be used for realizing P wave alarm. DI value is directly related to the seismic intensity and earthquake damage. With a continuous calculation of DI, P and S wave alarm can be issued (when PI exceeds the preset level P wave, and when ordinary monitored values or DI value exceed preset level S wave alarm can be issued). Detailed explanation of P wave detection methos was described in Nakamura (l996). This system is very simple and it works with single station. Because of this, it is easy to apply it to all important lifeline structures like pipelines, power plants, railways and bridges. Combination of this alarm system with vulnerability information of the ground and structures estimated with other methods is promising for future early warnings, since it makes possible to understand the areas that will be vulnerable during the earthquakes.