Earthquake Early Warning in Japan中村 洋光
Hiromitsu Nakamura
防災科学技術研究所
National Research Institute for Earth Science andDisaster Prevention, Japan(NIED)

OutlineOverview of the earthquake early warning (EEW)
system in Japan
Transmission and utilization of the EEW
Problems of the present EEW system

Earthquake Early Warning（緊急地震速報 Kinkyu Jishin Sokuho）

From JMA Web site
The EEW system provides advance warning of estimated seismic intensities andexpected arrival time of S-waves. These estimates are based on prompt analysis ofhypocenter location and earthquake magnitude using data observed by seismographs
near the epicenter. The system issues several EEW messages during the course of
one earthquake, improving the accuracy of the warning as the amount of available
data increases.

Seismic stations for EEW

NIED：Hi-net（800 stations）••

High-sensitivity seismograph
Borehole with depth of 100 m
or deeper

JMA：network for tsunami warning●NIEDand earthquake information services（200 stations）▲JMA•

Strong-motion seismographMethod for determining hypocenter location
Single station
B-Δ method
通常の波形表示1秒

Function fitting

振幅絶対値対数表示

Slope Ｂ

1秒

Ｂdecreases withdistance and showsindependence frommagnitude

JMA uses several methods to determine hypocenter
location, each optimized to the number of stations
available. These methods are applied to the data
observed at 200 JMA stations.
The not-yet-arrived method developed by NIED is
applied to the data observed at about 800 Hi-netstations.
1–2 stations
Territory Method

2 or more stations
Not-yet-arrived method

3–5 stations
Grid Search method

Real-Time Earthquake Information System (REIS)by the not-yet-arrived method applied to Hi-net data
voice alarm
focalmechanism

estimatedintensity

countdown toS-wave arrival

receiverpoint

epicenter

seismograms
and computedP arrival

S-wave front

stationamplitudes

REIS can be used to determine earthquake parameters andthen transmit these results to JMA in order to issue an EEW.

Earthquake Early Warning System in Japan

The practical service of EEW in Japan has been in
operation since Oct. 2007.

Utilization of EEW
Cell-phonecell-phone alert
consists of analarm and text.

Receiving terminal

PC software

EEW
Offshore Ibaraki
Pref. Warningfor strong
shaking. JMA

Tens of millions
Personal safety

hundreds of thousands
Automatic controlProblems of the present EEW system(1) Sometimes EEW is issued after S-wave arrival
Warning times become negative within an area about 30km from theepicenter. When a large earthquake occurs, the closer to the hypocenter
the greater the likelihood of damage.

(2) Underestimation of seismic intensity during a
massive earthquake
In the 2011 Tohoku-Oki earthquake (M9), the EEW was issued to thearea close to the hypocenter earlier than the S-wave arrival. But the EEWcannot be issued to areas further away from the hypocenter, where theobserved seismic intensity is greater than 5-lower.

(3) False alarm
Earthquakes sometimes occurred simultaneously over the entire fault
region, such that the EEW system became confused, and didn’t always
determine the hypocenter location and earthquake magnitude correctly.

Time delay of first EEW reports andnegative warning area -problem(1)Histogram of the time delay in issuing
the first report after P-wave arrives atthe closest station7060

地震数event

50

Data: 197 evens withIs greater than 4 since
2007

Warning time before S-wave arrivals
2008 Iwate Miyagi inland earthquake

Negative warningarea

4030201005101520
地震を検知してから第1報が提供されるまでの時間（秒）Time delay of first report (s)peak at 3 to 5 seconds that roughly corresponds to an area
within 30 km of the epicenter where warning time is negative.

Importance of Near-field Strong Ground Motion
Data for EEW2008 Iwate-Miyagi inland
earthquake

Off -line analysis result
warning time of the timing of over intensity
5-lower observed at IWTH25 where theepicentral distance is about 3km
Comparison of near-field strong motion
data observed at KiK-net IWTH25(epicentral distance 3km) and timing ofEEW

Warning time offirst EEW report (JMA)First EEW report
08:43:54.2

P-wave08:43:46.7
ACC. EW

Negative warningarea

Seismic intensity

The negative warning ACC. NS
area is within a few
km from the epicenter ACC. UD
Real –timeSeismic intensity

Over intensity 4.5
08:43:48.0
Time(s)Strong-motion real-time monitoring system fora specific active fault earthquake
Near-field strong ground motion data are very effective in reducing
the size of the negative warning areaseismographreducing the size of thenegative warning area
30km or more

a few kmfault

110 Major active fault zones, that have a high level ofactivity and great social and economical influence, wereselected and have been evaluated as the targets offundamental surveys and observations by HERP.

Observation system is installed closed
to a specific active fault.
The seismograph calculates various
strong-motion parameters in real-timeDevelopment concepts
Monitoring system must accurately observe extreme strongmotion near active fault zone.
The full scale of the accelerometer is up to 8 G
Each observatory has two strong-motion
accelerometers on the surface and at a depth of 50 m toproduce reliable on-site information
Borehole-type accelerometer is downsized for
installing in urban area.
For decreasing the area of negative warning
Recording data in high sampling rate of 400Hz
The seismograph calculates various strong-motion
parameters in real-time (B-delta, PGA, PGV, PGD andreal-time intensity etc.)
The packet length used for transmission is shortened to0.1 s to reduce delays in transmission

Strong-motion observation network
closed to the Miura-hanto fault group
Distribution map ( )Kinugasa/Kitatake
fault zone

Takeyama
fault zone
KNG053K-NET
KiK-netKNG051surface

KNG052
KNG05410km
South part fault zone

Observed data (waveform and calculated intensity )is transmitted to NIED center in real-time

4m

borehole (50m)

The EEW of the 2011 Tohoku-Oki earthquake
Warning area-problem(2)Area where the observed seismic intensity
is greater than or equal to 5-lower

Breaking news on TV

The EEW was issued
8.6s after the P-wave
arrives at the closest
station to the hypocenter.
The S-wave front had
not yet arrived on land.

underestimation

This underestimation can probably be attributed to theamplitude-magnitude (MJMA) saturation for events of Mw
greater than 8 and the large extent of the fault rupture, anextent of about 40,000 square kilometers.

What should we do?
EEW

Real-time monitoring ofstrong motion

Prediction of strong motion
by determination of
hypocenter location andearthquake magnitude using
P-wave data.

Live monitoring of strong
motion is independent of theestimation of EEW.

The use of both types of data will improve theaccuracy of warning information.

Warning test of the 2011 Tohoku-Oki earthquake
Off-line analysis of on-site warning

EEW

using K-NET & KiK-net data

Actually issued

The on-site warning for eacharea is issued when theobserved real-time seismic
intensity exceeds a specificthreshold.
In this analysis, the warning
threshold is seismic intensity
4 in real-time.

The EEW can be issued early to the area near the hypocenter.
The on-site warning can be issued to the area where the EEW can’t besufficiently responded.

Conclusions
The NIED has developed the real-time earthquake
information system (REIS) which is able to determine
hypocenter locations and earthquake magnitude within afew seconds.
The JMA has been issuing EEW, which contain the resultsof REIS, to the general public since October, 2007.
The EEW is transmitted to many kinds of devices and used
for personal safety and automatic control.
It is very important to observe strong motion in real-timeusing a dense network in order to improve the EEW system.