JOINT CONFERENCE PROCEEDINGS
9th International Conference on Urban Earthquake Engineering/ 4th Asia Conference on Earthquake Engineering
March 6-8, 2012, Tokyo Institute of Technology, Tokyo, JapanCOMPARISON OF THE P-WAVE EARTHQUAKE ALARM BY MULTI-STATION AND
SINGLE-STATION DETECTION SYSTEMS
Tsutomu Sato 1) and Yutaka Nakamura2,3)
1) Research Engineer, System and Data Research, Tokyo, Japan
2) President, System and Data Research, Tokyo, Japan3) Visiting Professor, Department of Built Environment, Tokyo Institute of Technology, Japantsato@sdr.co.jp, yutaka@sdr.co.jp

Abstract: The earthquake motion of the 2011 off the Pacific coast of Tohoku Earthquake grew gradually larger andcontinued unusually long with high amplitude more than JMA intensity 4 in wide area. The single-station detection
system FREQL succeeded to issue the P-wave alarm and estimated the earthquake parameters, although it took 15
seconds between detecting the earthquake to issuing the alarm. Proposed technique estimates the origin time and location
using the least squares method from the P-wave detection time of at least 5 sites. In case of the 2011 off the Pacific coastof Tohoku Earthquake, the first P-wave detection was MYG011 Oshika station and then the location estimated after 3.67
seconds. After the magnitude grew up, P-wave alarm can be issued around 6 seconds after P-wave detection. Because
P-wave alarm with single-station observation could be issued 14 seconds after P-wave detection, multi-station
observation method can be expected to shorten the alarm time for 8 seconds.

1. INTRODUCTION
The earthquake motion of the 2011 off the Pacificcoast of Tohoku Earthquake (hereafter the 3.11 earthquake)grew gradually larger and continued unusually long withhigh amplitude more than JMA intensity 4 (corresponding toMMI 7) in wide area. Although final seismic intensity
reached 6+ (corresponding to MMI 10-11), there wasrelative little damage caused by the earthquake motion. In
such situation, some early warning system had worked toissue alarm before large motion, but many of them could not
performup
toexpectation.
Especiallyasingle-station-detection early warning system developed byJMA, Japan Meteorological Agency, could not recognize the3.11 earthquake danger and not issue the warning. And alsothe alarm for Shinkansen, bullet train, was delay, and thealarm system is based on the JMA system replace after the2004 Niigata-ken Chuetsu earthquake. Fortunately, no highspeed train run into a damaged area, but the train had a risky
condition. At the time of the 2004 Niigata-ken Chuetsu
earthquake, Compact UrEDAS, the other early warning
system for JMA system, that worked as expected and keep
safety for the passengers and crews, totally 154 persons, hadbeen replaced for Shinkansen train. A single-detection early
warning system FREQL is a successor of UrEDAS andCompact UrEDAS. One FREQL station nearby base ofOshika Peninsula succeeded to detect the 3.11 earthquake,
issue P wave alarm and determine the earthquake parameters
reasonably without magnitude. But it needed 15 seconds toissue P wave alarm.

So this paper compares the early P wave alarm
between ordinal FREQL single estimation and the othermulti-detection method using FREQL technique, and thenconsiders a possibility of earlier earthquake warning.

2. ESTIMATION OF EARTHQUAKE PARAMETERS
USING MULTI STATION INFORMATION

2.1 Estimation of origin time and location of a source
Origin time and location of a source (Latitude,Longitude and depth) are estimated from a time of P wave
detection of more than five stations using least squares
method, assuming a P wave propagation velocity 6 km/sec.
Consideration below uses strong motion records of K-NETand KiK-net and assumes that the station has an instrument
corresponds to FREQL and send a time of P wave detection
in real time, and monitors a detection, an alarm, growth ofmagnitude and so on. That is, initial estimation is done withP wave detection information from first five stations, and theestimation is updated as often as receiving the informationfrom the other station and the result is compared with theresult before. If the scatter of the results are in predefined
range (5 km in this paper), the result is fixed. If a density ofstrong motion observatories is less than 20 km, it will beexpected that the location is fixed within 4 seconds after firstP wave detection. In case of 2004 Niigata-ken Chuetsu
earthquake and 2010 Taiwan Kaohsiung earthquake, thesource locations are determined in 1.04 second and 1.69seconds after P wave detection, respectively. In contrast, theJMA method with multi observation required 5.4 seconds inaverage and 5.4 seconds for issuing the first information forthe 3.11 earthquake.
2.2 Estimation of magnitude
Magnitude is estimated by a formula below(Takayama et al, 1981), based on the amplitude of P wave
and its frequency by Gutenberg-Richter.
M=1.59(logVp＋logR)+1.53(1)Here, Vp is P wave amplitude of vertical motion in mkine (=0.001 cm/sec) and R is epicentral distance in km. Althoughequation (1) supposes that the value of Vp is observed on ahard ground, K-NET station is not always installed on a hardground. So the earthquake motion amplification factor A foreach station is estimated as Table 1 based on the estimate
formula for seismic intensity (Saita et al, 2005), andequation (1) is modified as follows.
M=1.59(logVp+logR)+1.53-1.59logA(2)

Although epicentral distance is calculated based on a rupture
start point estimated in first few seconds, epicentral distancewill be changed by the progress of fault rupture. And also
main shock will arrive after the initial motion. So equation(2) can be adopted for a time window R/4Cr after P-wave
detection, a rupture time for 1/4 of the epicentral distancefrom the start point of the rupture. In this time, the scatter ofthe estimated magnitude is less than +/- 0.2 during theapplying time.
After fixing the epicenter, magnitude is estimatedfrom equation (2) and then the P wave alarm is issued basedon the M-∆ relation if a station seems to be danger. Because
this method can grasp the location of the earthquake
relatively accurately, it is possible to determine an area
needed alarm with tremendous precision. Finally averaged
magnitude will be the magnitude of whole system. In thispaper concerns the change history of the estimatedmagnitude for the 3.11 earthquake and the 2008 Iwate andMiyagi earthquake.
3. RESULT AND DISCUSSION
In case of the 2008 Iwate and Miyagi earthquake,
information from five stations is observed 3.46 seconds after
first detection at IWTH25 Ichinoseki-Nishi station, and thelocation of the epicenter is determined latitude 39.008˚N,longitude 140.875˚E and depth of -4.6 km. Then after 0.55
seconds, information from MYGH02 Naruko station wasadded and the location of the epicenter moved to latitude
39.027˚N, longitude 140.867˚E and depth of -2.1 km.
Because the difference was within 5 km, the estimation wasfixed. The depth was minus value but less than 5 km so thedepth fixed as 0 km. Also, the epicenter by JMA was latitude
39.028˚N, longitude 140.880˚E and depth of 8 km.
In case of the 2011 off the Pacific coast of Tohoku
Earthquake, information from five stations is observed 2.54
seconds after first detection at MYG001 Oshika station, andthe location of the epicenter is determined latitude 36.376˚N,longitude 146.094˚E and depth of 381.6 km. Then after 1.13
seconds, information from MYG010 Ishinomaki station wasadded and the location of the epicenter moved to latitude
38.023˚N, longitude 143.331˚E and depth of 10.8 km. The
difference of estimation was quite large. After 0.89 seconds,
information from MYG030 Towa station was additionallyarrived and the location of the epicenter moved to latitude
38.003˚N, longitude 143.356˚E and depth of 81.1 km.
Because the difference of the location is within 5 km but thedepth was quite differ for each other but the reliability of thedepth at this station was low, the fixed estimation became
the second one with 4.56 seconds. Also, the epicenter by
JMA was latitude of 38.103˚N, longitude 142.860˚E anddepth of 24 km.
Figures 1 and 2 show the progress of the magnitude
based on equation (2) with the information of first sixstations for each earthquake. Information of FKSH03
Takasato station was added as an example of little far station
as a reference for both figures.

Table 1 The amplification characteristics at station of K-NET and KiK-net
Site
MYG011
MYG008MYG002
MYGH03
MYGH12
MYG010
IWTH25
IWTH26
IWT010
AKT023
IWTH24
MYGH02
FKSH03

OshikaKitakami
UtatsuKarakuwa(kik)Shizugawa(kik)Ishinomaki
Ichinoseki-W(kik)Ichinoseki-E(kik)Ichinoseki
Tsubakidai
Kanegasaki(kik)Naruko(kik)Takasato(kik)Sum ofdata9111413131210119810612Averaege of RI
amplification
1.504
0.749
1.203
0.375
0.350
1.683
0.854
1.203
0.805
0.500
1.133
0.136
1.128

Dispersion of2logA
0.885
0.602
0.570
0.589
0.629
0.864
0.740
0.858
0.888
0.706
0.771
0.712
0.319

Constant termof Fig.(2)
0.33
0.93
0.57
1.23
1.25
0.19
0.85
0.57
0.89
1.13
0.63
1.42
0.63

S
wave arrival.
Ｓ波到着時刻高郷を除くTakasato) Ichinoseki-W(exclude

Tsubakidai Ｍ fixed
Ichinoseki-E Ｍ fixed Naruko Ｍ fixed
Ichinoseki-W Ｍ fixed

9MedutingaM

8Tsubakidai
Kanegasaki Ichinoseki-EM7.2 by JMA

7Ichinoseki

Takasato
at Takasato,

6S wave arrival is later.
Ichinoseki Ｍ fixed
Takago Ｍ almost fixed

Naruko5Kanegasaki Ｍ fixed

43-2-10
1
23Time from earthquake detection (sec)

45Figure 1 The growth of magnitude of the 2008 Iwate and Miyagi Earthquake
karakuwa Ｍ fixed Kitakami Ｍ fixed
Shizugawa Ｍ fixed
Utatsu Ｍ fixed
Shizugawa
Kitakami
Alarm level Ｍ7.7
karakuwa

98MedutingaM3-50awiaamawgkuuzakithair
SKat
Ktatamamrarmallraaalev
eav
eaav
wwawPPP

Ishinomaki

ikuasm to tan Uihst
Iat marm ar laaleave av
waw PP

5akihsOtamralaev
awP

6

Takasato
TakasatoＭ

SＳ波到着時刻
wave arrival.
Takasato
高郷
高郷を除くTakago)(exclude74Utatsu Oshika

M9.0 by JMA

Ishinomaki Ｍ fixedOshika Ｍ fixed

510152025
Time from earthquake detection (sec)3035

Figure 2 The growth of magnitude of the 20112011 off the Pacific coast of Tohoku Earthquake
In case of the 2008 earthquake, applicable time is only
1-2 seconds for the first six stations and the magnitude grew
drastically and reached and was fixed 7.2 around one second
after detection. In case of FKSH03 Takasato station about
170 km away, the magnitude grew relatively slow andstopped within about three seconds. Then it was fixed about
7.
In case of the 3.11 earthquake, applicable time wasabout 13-15 seconds during the growth of the magnitude andthe magnitude was fixed. In case of FKSH03 Takasato
station about 300 km away, the magnitude grew yet slower
and stopped after the applicable time. The magnitude wasreached or estimated to reach further more than 8 finally foreach station. Magnitude 7.7 seems to be the alarm level foreach station based on the M-∆ relation and the alarm could
be issued mainly about six seconds and 15 seconds at least
after detection. Thus it shows that it is possible to issue thealarm six seconds at the earliest after detection. For example
Karakuwa station detected P wave at 14:46:40 and issued
14:46:46. Because in case of the single-station detection
system seen in Figure 3, the alarm seemed to be issued at
14:46:54, this multi-detection method can be expected togain time 8 seconds. Figure 3 shows the alarm time of themulti-detection method on the time-line of real time intensity
RI (Nakamura, 2003) with RI = 1.5 as P wave alarm level.

Scale of real-time seismic intensity RI : 5
PI alarm at IshinomakiIshinomaki RI=0.0

Corresponding to Hypocentral distance

PI alarm at Shizugawa

PI alarm at Karakuwa
Shizugawa RI=0.0
Karakuwa RI=0.0
Utatsu RI=0.0

PI alarm at Utatsu

Kitakami RI=0.0

PI alarm at Kitakami.
dexi
fecruosfoe
mitehT

noitcetedevaw
Pfoemitht6

noitcetedevaw
Pfoemitts
135(The fastest alarm by FREQL)

P-alarm at Kitakami, Karakuwa
and Shizugawa using Multi-FREQLinformation4045
Standard time in Japan:

PI alarm at Oshika
Oshika RI=0.050
2011/3/11 14:46:**

55

Figure 3 P wave alarm time of first 6 sites of the 20112011 off the Pacific coast of Tohoku Earthquake
4. CONCLUSIONSThis paper compares between the early P wave alarmusing multi-detection method with FREQL P wave detection
and that of single-station detection. As a result, a tendency isseemed that the slower magnitude grew, the farther thestation locates. Although P wave alarm is relative earlier forthe distant earthquake, it is confirmed that some station canissue earlier alarm with the multi-detection method and moreexact magnitude and location of the epicenter can bedetermined promptly. Because the exact earthquake
parameters are fundamentals for proper countermeasuresoon after the event, we would like to construct a system tograsp the source information in a certain level of accuracy
for disaster prevention under isolation of the information.
Acknowledgements:
In this paper, the waveform data was mainly provided by
K-KET and KIK-net of NIED, National Research Institute for Earth
Science and Disaster Prevention. The authors would like tosincerely express our highest appreciation and gratitude to people
and the organizations.

References:Takayama, A., Emoto, Y,. Abe, H., and Nakamura, Y. (1981), “Astudy of earthquake early warning system,” JSCE Magazine,Vol.66, No.5, 51-56.
Saita, J. and Nakamura, Y. (2005), “The development of a formulafor seismic intensity estimation added the characteristics onstrong motion observation,” Proceeding of the 4th Annual
Meeting of Japan Association for Earthquake Engineering,308-309.
Nakamura, Y. (2003), “EXAMINATION OF A RATIONALSTRONG MOTION INDEX - Relationship between the DI
value and the other strong motion indices -,” Abstract Volume ofthe 27th JSCE Earthquake Engineering Symposium, 54.
Sato, T. A. and Nakamura, Y. (2005), “The seismic source
estimation using the variation of seismic damage intensity DI
value at 2004 Niigata-Chuetsu earthquake,” Proceeding of the
4th Annual Meeting of Japan Association for Earthquake
Engineering, 298-299.