New Stand-Alone and Advanced Earthquake Early Warning Systems Designed to Protect Railways

A new earthquake detection and warning system that uses single station records was designed. The system determines the location and magnitude of an earthquake and issues an alarm immediately after arrival of the P wave (primary wave or longitudinal waves). In the conventional system now in use with Shinkansen (“bullet”) trains, magnitude is first determined and then distance is evaluated. In the new system, the distance to an epicenter is initially determined, followed by the magnitude. Findings have shown that the initial rate of increase in P-wave amplitude is inversely proportional to the epicentral distance. This relation can be used to estimate the distance in a time interval as short as 2 or 3 s after arrival of the P wave. Then an estimate of magnitude can be made from the maximum amplitude observed within any given time interval after P-wave arrival. This method is preferable to the conventional one because larger earthquakes involve longer rupture times, and it is questionable whether magnitude can be estimated correctly in such a short time after arrival of the P wave. Another new system uses earthquake early warning (EEW) information. The Japan Meteorological Agency (JMA), which has a seismic network that covers all of Japan, is responsible for routine earthquake and tsunami observations. The new system receives EEW information from JMA together with the information obtained by railway facilities, executes a risk assessment for the areas concerned, and issues an earthquake warning if necessary. The system could effectively cover most of Japan, and the reliability of the information provided may be far better than that produced by the stand-alone system. Also, the system could significantly improve outcomes to early adjustments of train operations in the event of an earthquake

The 1998 Miyako fireball\u27s trajectory determined from shock wave records of a dense seismic array

A high velocity passage of a meteoroid through the atmosphere generates a shock wave with a conical front. When the shock front arrives at the surface, it causes high frequency ground motions that are registered on the seismograms. We can use seismological data to determine the trajectory of the meteoroid in the atmosphere. A strong shock wave from the 1998 Miyako fireball is recorded by more than 20 stations in a dense array of seismographs installed in the northeastern region of Honshu Island, Japan. We determine the velocity and the trajectory of the fireball in the upper atmosphere using the arrival times of the shock wave at the stations

Determination of the fireball trajectory using dense seismic arrays

Fireballs, which are caused by high-velocity passages of meteorites through the atmosphere, generate shock waves. It has been known that such shock waves are often recorded on seismograms. It is possible to determine the trajectories and the sizes of a fireball using seismological records. We have searched shock wave signals from many bright fireballs observed in the period from September 1996 to November 1998, and the 1999 Kobe meteorite. The shock waves from one large fireball, which is called the Miyako fireball, and the Kobe meteorite are clearly recorded on many seismograms. In particular, the shock waves from the former fireball are widely recorded by the dense seismic array of 1997-98 joint seismic observations in the Tohoku Backbone Range. We determine their trajectories. Amplitudes of the shock waves are found to be possibly correlated with the masses of the meteorites. It is also indicated that the shock waves from fireballs, which are darker than brightness magnitude -10, are too weak to be recognized on the seismograms of ordinary seismic stations in Japan