Volume 6, Number 3, October 2008

NATIONWIDE EARTHQUAKE EARLY WARNING IN JAPAN:
INFORMATION BEFORE STRONG GROUND SHAKING
Just before an earthquake strikes a population center, a new Japan Meteorological Agency (JMA) earthquake
communication system warns the public about the hazard. The warning is called “Earthquake Early Warning” (EEW).
This innovative new warning service has been initiated nationwide in Japan. For example, when the warning isreceived at railway centers, the control room of the railway company gives an emergency notice to train drivers to stop
their trains immediately. In buildings, elevators stop at the nearest floor and automatically open their doors. In hospitals,
surgeons are alerted to temporarily suspend their surgical operations to avoid risk to patients on the operating table.
The hypocenter and magnitude of the earthquake are rapidly determined using available data at stations near thehypocenter and distribution of strong ground shaking is quickly predicted. The information is immediately delivered tothe population. Although it is currently impossible to predict earthquakes before they occur, it is possible to warn people
in the vicinity of the hypocenter before they experience strong ground shaking
An M7.2 earthquake occurred at Tohoku district, Japan, on 14 June 2008 (Iwate-Miyagi Nairiku Earthquake). The firstwarning was disseminated 3 seconds after the first detection of the P wave at the closest seismic station. Although thedissemination was later than the arrival of the large amplitude S wave at the cities closest to the epicenter, it was earlier
by approximately 15 seconds at Sendai city, the largest city of the Tohoku district. People were aware of theearthquake before the city experienced strong ground shaking.
Even though the interval -- relatively short (counted in seconds) -- between the time when the EEW alerts thepopulation and when the population actually experience strong ground motion the EEW is an important and powerfulwarning tool to reduce loss of lives and human injuries from earthquakes by alerting the citizens within sufficient time totake appropriate safety measures in advance of strong ground shaking.
Contact: Dr. Mitsuyuki HOSHIBA, Seismology and Volcanology Research Department, Meteorological ResearchInstitute (MRI), Japan Meteorological Agency. mhoshiba@mri-jma.go.jp

Figure 1: Arcs represent elapsed time (in seconds) from EEW to S wave arrival for Iwate-Miyagi Nairiku Earthquakeon 14 June 2008 (M7.2). The differences of color show the observed seismic intensity on JMA scale.

ENVIRONMENTAL WIND SHEAR MAY CONTROL NEAR-SURFACE WIND
DISTRIBUTIONS IN TYPHOONS
Traditionally, typhoon wind fields are approximated by adding its movement velocity to the associated swirling winds,
which results in stronger winds on the right side of the storm track. However, recent studies revealed that environmental
vertical wind shear (i.e., large-scale wind difference between upper and lower tropospheric levels) also could contributeto the typhoon-related wind asymmetries. Generally shear tends to affect near-surface wind fields in such a way that
azimuthal winds increase (decrease) on the left (right) side of the shear vector (looking down on the typhoon). Figure 2
shows an example of such a shear contribution taken from the JMA meso-scale analyses.
2006 8 7 18 UTC

2007 9 16 6 UTC
10.0+
13.0+
1.5

10.0+34.1+
31.5
1.7
10.0
20.0

10.0+5.9+ 2.0
34.2

30.0+
12.4
20.0+
31.8+
16.6

10.0+
13.1

T0607 (MARIA)

10.0

T0711 (NARI)

Figure 2: Isotachs for near-surface winds of Typhoons MARIA in 2006 (left) and NARI in 2007 (right) along with shear
vector (pink-colored arrow) and storm motion (blue arrow).
Contact: Mr. Mitsuru UENO, Typhoon Research Department, Meteorological Research Institute (MRI), Japan
Meteorological Agency. mueno@mri-jma.go.jp