Understanding
Earthquakes

The Headquarters for

Earthquake Research PromotionUnderstanding Earthquakes

Understanding Earthquakes

Introduction
This booklet is written to help people better understand earthquakes. In preparing

Supporting Section

this booklet a great deal of data and information has been provided by many
institutions and researchers. We are extremely grateful to them.

PART 1  Government Efforts… …………………………………………………………………… 24
I. General Overview of the Headquarters for Earthquake Research Promotion… ……… 24

Contents…………………………………………………………………………………………………… 2
Recent earthquakes in Japan and around the world… ……………………………………… 4

Q&A

1. The basic objectives and roles of the Headquarters for Earthquake
Research Promotion… …………………………………………………………………… 24
2. Composition of the Headquarters for Earthquake Research Promotion… ………… 24

PART 2  Applying the Outcome of Investigative Earthquake Research for Disaster Prevention… … 25
I. Long-term Evaluation… ……………………………………………………………………… 25

Q1 Why do we have so many earthquakes in Japan?……………………………………………… 6

The results of long-term evaluation along the main active fault zones……………… 25

Q2 How do earthquakes occur?… …………………………………………………………………… 7

The probability of earthquake occurrence and the probability of other accidents

Q3 What is an active fault?… ………………………………………………………………………… 8

or disastrous events………………………………………………………………………… 26

Q4 Do earthquakes not happen in places where there are no active faults?…………………… 9

Results of long-term evaluations of Subduction zone earthquakes… ……………… 26

Q5 Do earthquakes repeatedly happen at the same places?… ……………………………… 10

II. Seismic Hazard Maps………………………………………………………………………… 27

Q6 How often do large earthquakes occur?… …………………………………………………… 11

Basic use of seismic hazard maps… …………………………………………………… 27

Q7 How do seismic waves travel?… ……………………………………………………………… 12

Utilization of the“Seismic Hazard Map”………………………………………………… 27

Q8 In what place does the ground shake the strongest?… …………………………………… 13

Probabilistic Seismic Hazard Maps… …………………………………………………… 28

Q9 How long does the ground shake for?………………………………………………………… 14

Seismic Hazard Maps for Specified Seismic Source Faults… ……………………… 29

Q10 What is“long-period ground motion”?………………………………………………………… 15
Q11 What are the hypocenter, epicenter and hypocentral areas?……………………………… 16
Q12 Are seismic intensity and earthquake magnitude different?… …………………………… 17

Supplementary Material Section

Q13 What are“main shocks”and“aftershocks”?………………………………………………… 18

Measures you can take to stay safe from earthquakes… ………………………………………… 30

Q14 What are“earthquake swarms”?… …………………………………………………………… 19

1. Before an earthquake occurs… …………………………………………………………………… 30

Q15 How are tsunamis generated?… ……………………………………………………………… 20

   10 Ways to Prepare for an Earthquake…………………………………………………………… 30

Q16 What is“liquefaction”?… ……………………………………………………………………… 21

2. If an earthquake occurs……………………………………………………………………………… 30

Q17 Is it possible to predict earthquakes?… ……………………………………………………… 22

   10 Tips for Earthquake Safety……………………………………………………………………… 30

Q18 What is an“earthquake early warning”?……………………………………………………… 23

2

3

Understanding Earthquakes

Understanding Earthquakes
The huge earthquake that occurred off Sumatra Island, Indonesia in 2004 caused an enormous tsunami. The tsunami caused

Recent earthquakes in Japan and around the world

tremendous damages to the countries facing the Indian Ocean. Large earthquakes like this that inflict serious damage occur repeatedlyaround the world. Living in Japan, one of the world’s most earthquake-prone countries, we should never forget that we have also
suffered severe damage from many earthquakes. These include the Hyogoken-nanbu Earthquake (The Great Hanshin-Awaji
Earthquake Disaster) in 1995 and the off the Pacific Coast of Tohoku Earthquake (The Great East Japan Earthquake Disaster) in 2011.

Earthquakes
around the world(Photo: Provided by Mr. Katsuyuki Abe)

(8) The 1989 Loma Prieta Earthquake (U.S.), M7.1

(Photo: Provided by Mr. Katsuyuki Abe)

(10) The 1999 Jiji Earthquake (known in Taiwan as the 921 earthquake) in Taiwan, M7.78(9) The 1990 Luzon Earthquake (Baguio City, the Philippines), M7.88

0
0
9
1

Earthquakes
in Japan

11

13

10
9

12

(Photo: Provided by Mr. Takehiko Yamamura)(11) The 2003 Bam Earthquake in the south-east part of Iran, M6.8

114

(Photo: Provided by the National Museumof Nature and Science, Tokyo)(1) The 1923 Great Kanto Earthquake, M7.9

(Photo: Provided by Mr. Akira Nose)

62 killed(12) The 2004 Sumatra Earthquake (also known as the Sumatra-Andaman earthquake), M8.8
2,413 killed(Photo: Provided by
Japan Meteorological Agency)(2) The 1946 Nankai Earthquake, M8.0

2,430 killed (Photo: Provided by Mr. Katsuyuki Abe)

(Photo: Provided by Mr. Katsuyuki Abe)00(3) The1993 Hokkaido-nansei-oki Earthquake, M7.8

02

More than 105,000
killed or missing

1,330 killed

43,200 killed(4) The 1995 Hyogoken-nanbu Earthquake, M7.3

(6) The 2008 Iwate-Miyagi Nairiku Earthquake, M7.2

More than283,100 killed

69,185 killed(Photo: Provided by Mr. Yoshiaki Nakano)

230 killed or missing(5) The 2004 Niigata Chuetsu Earthquake, M6.8

(13) The 2008 Sichuan Earthquake, M7.9

(14) The 2010 Chilean Earthquake oﬀ the central coast, M8.5
(7) The 2011 oﬀ the Paciﬁc Coast of Tohoku Earthquake on March 11, Mw9.0

3

6

7

5

6,434 killed (Photo: Provided by Mr. Katsuyuki Abe)
4

1

Mo than 521 killed (Photo: Provided by the InternationalMore

2

65 killed(Photo: Provided by Niigata Pref.)18,49318,49,49
493 killed (Photo: Provided by Miyako City, Iwate Pref.)Federation of Red Cross and
Red Crescent Societies)

23 killed (Photo: Provided by Iwate Pref. Ichinoseki General Branch Oﬃce of Iwate Kennan Wide Area Promotion Bureau)

45

Q1 Why do we have so many earthquakes in Japan?

Q2 How do earthquakes occur?

That is because Japan is situated on the plate boundaries, an area where large strains areaccumulated.

Earthquakes occur when stressed underground rock masses rapidly move in opposite directions toeach other along a certain plane (a fault plane). This movement is called fault movement (or faulting).

The surface of the earth is covered with more than a dozen huge plates (plate-like masses of rock). The plates move in

Along the Japan Trench and the Nankai Trough on the Pacific side of Japan, oceanic plates are continuously moving under

different directions at a speed of several centimeters per year (plate motion). Looking at things on a large scale, mostearthquakes occur in the belt-like zones along the plate boundaries. It is said that Japan has been struck by approximately ten
percent of the world’s earthquakes. This is despite its small area, being less than one percent of the world’s total land area.
Tremendous forces are applied by plate motion to the inside of the underground rock masses near the plate boundaries. Over
many years a vast amount of energy builds up inside the rock masses as a strain and accordingly stress is accumulated. If a rockmass fractures due to the accumulated stress, an earthquake occurs. Japan is situated along the boundaries of four plates. The

the continental plates (subduction). At the same time, the continental plates are being dragged inland.
The subduction of an oceanic plate stresses rock masses around the plate boundary. When the accumulated stress exceeds its
limit, a fault movement occurs. This leads the continental plate to rapidly jump up. This movement is a type of earthquake
called an inter-plate earthquake.
On the other hand, earthquakes can occur in oceanic plates. The stress accumulated inside the oceanic plate generates a fault
movement in the plate; this also causes an earthquake. This type of earthquake is called an intra-oceanic plate earthquake.

large strain energy accumulated in the rock masses therefore cause many earthquakes to be generated. However this doesn’t

In continental plates, indirect forces from plate motion accumulate strain energy. Fault movements occur to release this

only apply to the type of earthquakes that occur near the plate boundaries. Earthquakes that occur inland are also thought tostrain energy in the continental plate. They occur at depths of up to 20 km from the ground surface. When a large-scale fault

be the result of accumulated strain in continental plates.

movement occurs in a continental plate, a fault displacement may develop on or near the ground surface.
The Headquarters for Earthquake Research Promotion calls earthquakes that occur along or around a plate boundary related
to a trench or trough a “subduction zone (trench type) earthquake”. It also calls earthquakes that occur at the shallow section of

North American plate

he

il
ur

h
nc

a continental plate a “shallow inland earthquake.”e

TrContinental plate
Trench, trough

K

T
The
Japa
n Tre
nch

Eurasian plate

Oceanic plate
Shallow inland
earthquake

Inter-plate earthquake

Plate motion
Subductionof plate

Intra-oceanic
plate earthquake

Red arrows show
fault movements.

8 cm each year
1. Forces are applied to the rock mass.

ch

300

plane). The energy of strain
accumulated by plate motion in

4. The fault movements release
the strain energy.

Focal depth
0

Force

Tren

N

Philippine Sea
plate

600km

Epicenter data (2003 to 2012, greater than M4) are provided by the Japan Meteorological
Agency.
The arrows show the relative direction and speed of the Pacific plate and the Philippine Sea
plate to the Eurasian plate, respectively.
The thick solid lines show the plate boundaries. The dashed line shows unclear plateboundaries.

Earthquakes occur as fault
movements. A fault movement isa phenomenon that involves two
adjacent rock masses moving in
opposite directions to each otheralong a certain plane (a fault

wara

The

oto

-sh

ei
ans

ch

n
Tre

Force

gasa

3 to 5 cm each year

Izu-O

nk

Na

Paciﬁc plate

The

The

ugh

ro
ai T

2. Strain energy is accumulated
in the rock mass.

3. Fault movement starts fromthe hypocenter, resulting inan earthquake.

the rock mass is released in theform of a seismic wave. This isdue to abrupt faulting.

Fault plane

震源
Hypocenter○ shows the locations of epicenters. The color shows the depth of each hypocenter. You
can see that the earthquakes are concentrated along the areas near plate boundaries.

67

Q3 What is an active fault?

earthquakes not happen in places
Q4 Do
where there are no active faults?

An active fault is a fault that has repeatedly experienced fault movements in the past and is still
deemed to be a source fault of future earthquakes.

Earthquakes can occur where no active faults have been recognized.

If a large earthquake occurs inside a continental plate, the fault displacement can reach the ground surface and deformIf the magnitude of the earthquake is small, the displacement of the causal fault does not always show up on the groundgeological layers and geographical features. The deformations caused by repetitive fault movements such as these form

surface. Even if the fault displacement reaches the ground surface, sometimes such evidence of the fault activity is removed bycharacteristic geographies. These can include dislocations along mountain ridges, dislocations along valley faults, anderosion or sedimentation over a long period of time. Therefore, even in places where no apparent active faults have been

continuous cliff formations. By surveying these characteristic geographies through aerial photography, it is presumed that

presently found, active faults may still exist and cause earthquakes in the future.

approximately 2,000 active faults currently exist in Japan. Excavating active faults is useful for estimating the probability of

Detailed investigations of underground areas and geography may lead to detection of such underground faults.

fault activity in the future. By undertaking the excavations, we can find out the scale and interval of earthquakes in the past.

A fault apparent on the ground surface
Large-scale earthquakes with magnitudes 7 or greaterusually leave evidence of their activity on the groundsurface. As a result, underground faults can berecognized as active faults. However, in some cases,
such evidence can become obscured due to long-term
erosion or sedimentation.

The fault cliff that was formed as aresult of the fault movements that
occurred during the Nobi Earthquake
in 1891 (shown by the arrows). In
this earthquake, a total of 80 km of
surface fault rupture emerged along
the Nobi Fault. Active faults showthat earthquakes that form such acharacteristic geography haveoccurred repeatedly in the past.

Hypocenter

A fault that is notapparent on the ground surface
In most earthquakes with magnitudes smaller
than 6, no distinct evidence is left on the ground

Surface rupture

Approx. 6 m

Dislocation of geological layers generated by the Nobi Earthquake (theNeodani Fault).
A vertical displacement of approximately 6 m can be observed. Past
fault activities can be clarified byexamining the dislocation of layers
such as this one.
Fault
(Photo: Provided by the Education Committee of Motosu City)8

surface. It is therefore diﬃcult to recognize theunderground fault as being active.

Epicenter

Hypocentral
regionHypocenter

Earthquake source fault

Underground faults that have caused earthquakes are called“earthquake source faults.”
The dislocations that reached the ground surface as a result of faulting are called“earthquake surface faults (earthquake faults).”9

Q5 Do earthquakes occur repeatedly at the same places?
Large-scale earthquakes tend to occur repeatedly at the same place over a long period of time.
In Japan, it is well known that there are many active faults and places where large-scale subduction zone earthquakes repeat
all over the country.

Q6 How often do large earthquakes occur?
The intervals of subduction zone earthquakes, which occur near plate boundaries, range from several
decades to several hundreds of years. On the other hand, the intervals of active fault earthquakes,
which occur at inland active faults, range from a thousand to tens of thousands of years.
Subduction zone earthquakes, which occur near plate boundaries, occur at intervals ranging from decades to several

Large-scale earthquakes have a tendency of “happening repeatedly at the same place as in the past.” For example, records

hundreds of years on average. This is a relatively short period. Inland active fault earthquakes, on the other hand, occur atshow that at the Nankai Trough, where subduction zone earthquakes occur, large-scale earthquakes have been happening

intervals ranging from a thousand to tens of thousands of years. This is quite a long period compared with the human life-span.

repeatedly. The investigation of active faults shows that large-scale inland earthquakes also have repeated at the same fault as in

These intervals differ from fault to fault, because they depend on the speed of strain that is accumulated in the rock mass by

the past.

plate motion. They also depend on the strength of the rock mass against strain. However, earthquakes that are caused byindividual active faults have almost the same size and recurrence intervals.

Toi
-mi
sak
i Ca
pe

32

Ash
izur
i-mi
sak
i Ca
pe
Mur
otomis
aki C
ape
Shi
o-n
o-m
isak
Dai i Cape
o-za
ki C
ape
Om
ae-z
ak
Fuj i Cape
i Ri
ver

Taking all the earthquakes in Japan that inflicted major damage over the past 200 years, the average recurrence interval is 20

13
0˚

˚

Osaka Group
Approximately
300 m

Tosa Basin
Kumano Enshu Basin
Hyuga Basin
Muroto Basin Basin

˚

˚
140

136

138

˚

˚

32˚

134

˚

˚

The Nankai Trough The data used was provided by the Japan Coast Guard.
132

30



Osaka Group

Event(Earthquake)

GraniteThe 1930 Kita-izu Earthquake
Previous earthquake

Nojima Fault

+DNXKR 7HPPX (DUWKTXDNH

Before the above1LQQD(DUWKTXDNH<HDU(LFKR7RNDL(DUWKTXDNH.RZD1DQNDL(DUWKTXDNH





265

262



6KRKHL .RDQ 7RNHL(DUWKTXDNH6KRKHL .RDQ 1DQNDL(DUWKTXDNH0HLR(DUWKTXDNH

137
107
102



.HLFKR(DUWKTXDNH




6HDRI+\XJD

92
1DQNDL

Before the above

During the Hyogoken-nanbu earthquake, whichcaused the Great Hanshin-Awaji Earthquake
Disaster, the Nojima Fault in Awaji Island
moved. The Osaka Group, which had accumulated several million years ago, was displacedalong the Nojima fault by more than 300 m.

+RHL(DUWKTXDNH

147



Before the above

209

212



An average earthquake recurrence intervalof 700 to 1000 years

Before the above

203



years for subduction zone earthquakes and 10 years for shallow inland earthquakes.

90
7RNDL

1XPHUDOVRQWKHFRORUHGVROLGOLQHVLQWKHILJXUHVKRZWKHLQWHUYDOVRIRFFXUUHQFH <HDU 

Before the above
Before the above

The diﬀerence in the crossbar
colors stands for the diﬀerencesin the assumed values used forage estimation.

0

2000

4000

6000 years ago

The trench excavation survey at the Tanna Fault indicates that the Tanna
Fault moved nine times in the past, with an average interval of 700 of 1000
years. (The history of the fault activity was obtained by the Tanna Fault
Excavation Survey and Research Group in 1983.)$QVHL7RNDL(DUWKTXDNH$QVHL1DQNDL(DUWKTXDNH6KRZD7RQDQNDL(DUWKTXDNH6KRZD1DQNDL(DUWKTXDNH

5HOLDELOLW\RIHVWLPDWHGK\SRFHQWUDOUHJLRQV&HUWDLQ
3UREDEOH
3RVVLEOH
8QFHUWDLQ
2WKHUV(DUWKTXDNHVZLWKKLJKSRVVLELOLW\RIWVXQDPLV,QWHUSODWHHDUWKTXDNHVLQWKH6HDRI+\XJD 0FODVV

Before the above

A
A

A

A

1. Immediately after an earthquake, adiﬀerence in level is created on ground A,
which had been even before the quake.

C
B

B

A

A
3. After that another stratum, C, is deposited
with the same thickness on both ground A
and B.

2. A stratum, B, is then piled up on both sidesof the fault. B is thick on the lower side ofground A and thin on the other side.

C
B

C
B
A

A
4. Immediately after the next earthquake.
Processes 1. to 4. are repeated.

Such geological formations are found by
excavating active faults. They reveal that thefaults moved repeatedly in the past.

1011

Q7 How do seismic waves travel?
Part of the earthquake energy travels in the form of waves (seismic waves).

Q8 In what place does the ground shake the strongest?
The softer the ground is, the stronger the ground shakes.

When the underground rock mass is broken and a fault moves, part of the energy propagates in all directions as seismic

How strongly the ground shakes at the surface depends largely on the structure of deep ground near the surface. Generally,

waves. Typical seismic waves contain two different types of waves: P waves and S waves. P waves are the propagation of density

the ground shakes more strongly at surfaces where the soil near the surface is soft, compared to ground where the soil near thechange. The direction of P waves’ shake is the same as the direction of their propagation. S waves are the propagation of shear

surface is hard. Furthermore, sometime deep portions of ground also make the ground shake more strongly. This happens

deformation. The direction of S waves’ shake is perpendicular to the direction of their propagation. According to the direction

because seismic waves increase their strength when they propagate from hard rock mass to soft soil. They also increase theirof their shake, P waves and S waves are called “longitudinal waves” and “transverse waves,” respectively. P waves travel fasterstrength when the deflected waves and reflected waves overlap.

than S waves. That is why when an earthquake occurs first the ground rattles due to the arrival of P waves. After this theground slowly sways a little bit due to the arrival of S waves. Additionally, if an earthquake occurs in a distant place (especially

The underground structures near the surface can be estimated from geographical features to some extent. The deep groundstructures can also be known through boring investigations or studies using artificial earthquakes.

if the hypocenter is shallow) large and slow swaying can occur after the ground shake by P waves and S waves. Those waves arecalled surface waves and travel only on or near the surface of the ground. They are able to reach distant places.
P waves stand for primary waves, which means they come first. S waves stand for secondary waves, which means they come second.

How seismic waves look when ampliﬁedby underground structures

Hypocenter

Time duration

Time ofoccurrenceSoft ground
Direc

of w

ave p

ropa

S wa

ves

gatio

n

Obje

Slightly soft
ground

cts r

attle

P wa

a

se
c

on

ds

tion

Rock mass

Slightly hardground

ves

Direc

on

ds

tion
shak of
e
Swa

b

se
c

ying

Seismic wave

to an

d fro

ves
P wa

ves

nce t

12

5

10

Time (seconds)

Earthquake near Hakone on Aug. 5, 1990 (M5.1)
In the figure, underground structures such as rock mass and soft ground are simply
illustrated. The earthquake data (waveforms) shown in the figure are actual records.
The ground shakes approximately three times as strongly on the soft ground than it
does on the hard rock. The ground shakes for a longer amount of time on the soft
ground than it does on the hard ground. (This figure based on a figure by Mr. Kazuyoshi Kudo)

S wa

Dista

Velocity amplitude (cm/s)
10
0
-10
0

Poin

tA

ravel

ed by

the w

aves

Poin

tB

13

Q9 How long does the ground shake for?
The duration of large shakes in the large-scale earthquakes that occur near Japan is thought to begenerally one minute at the longest. The intensity of shake depends on the scale of the earthquake,the location of hypocenter, and the condition of the ground.
Generally, the larger that the earthquake source fault is, the duration of large shakes in the earthquakes that occur near Japangenerally becomes longer. For example, in the 1995 Hyogoken-nanbu Earthquake the length and breadth of the earthquake
source fault was several dozen kilometers. Subsequently, the duration of strong shakes lasted more than a dozen seconds.
On the other hand, during the 2011 off the Pacific Coast of Tohoku Earthquake both the length and breadth of theearthquake source fault were as large as several hundred kilometers. Subsequently, strong shakes lasted more than 3 minutes in

Q10 What is “long-period ground motion”?
It means a relatively slow swaying motion during earthquake shake.
When a relatively large-scale earthquake occurs, unlike ordinary earthquakes that have short shake periods, they occasionallycause slow swaying ground motions that last for a long period of time. The period can range from several seconds to more thana dozen seconds. Such ground motions are called “long-period ground motions”. Long-period ground motion can travel toplaces very distant from the hypocenter. Strong swaying motions can even be observed in places that are quite far from the
hypocenter. This is one of the features of long-period ground motion.

some areas. On the other hand, for example, during the 2003 Tokachi-oki Earthquake shakes have lasted for long periods ofSeismic intensity distribution
in the 2003 Tokachi-oki Earthquake

time, even if the earthquake source fault is not so large. In cases involving long periods of ground motion, slow swaying
motions may continue even after large shakes.
The magnitude of shake (seismic intensity) at a given location depends on the scale of the earthquake itself (earthquake
magnitude), it also relies on its position relative to the hypocenter and the underground soil structure. In the case of shallow

Intensity 1
Intensity 2
Intensity 3
Intensity 4
Intensity 5 Lower
Intensity 5 Upper
Intensity 6 Lower

inland earthquakes, strong shakes can come in the vicinity of the hypocenter and inflict severe damages even if the scale of theearthquake is relatively small.
(Photo provided by the Fire and Disaster
Management Agency)

Velocity amplitude

The 1995 Hyogoken-nanbu Earthquake (Chuo-Ku, Kobe City)

Churui Village(Now Makubetsu Town)

In this earthquake at Tomakomai Harbor, which
was 200 km or more away from the hypocenter, along-period ground motion caused the oil instorage tanks to slosh about. This caused the（cm/s）

50

tanks to rupture, leading to fire.

Hypocenter
Tomakomai City

100km

(Data taken from the Japan Meteorological Agency website)

North-south shake (cm)
−50
0

10

20

30

40

50

60

70

80

90

100
（seconds）

The 1995 Hyogoken-nanbu Earthquake: a large shake lasted for more than a dozen
seconds in Kobe City. During this time an extremely large shake lasted for 4 or 5
seconds.
(Data taken from the Japan Meteorological Agency website)

Churui Village

10
0
−10

Tomakomai City

10
0
−10

(Now Makubetsu Town)

0

20

40

60

80

100

120

140 seconds

From the seismographic data it can be seen that the swaying motion continued for a long time in Tomakomai,
even though it was very far from the hypocenter.

Large structures tend to resonate with long-period ground motions. It is now known that during the 1923 Great Kanto
Earthquake, there were large tremors with periods of more than 5 seconds. However these long-period ground motions did not

Velocity amplitude

The 2003 Tokachi-oki Earthquake（Tomakomai City）

attract much attention at the time. This was because back then there were not many large structures in Tokyo. However,（cm/s）

nowadays ultra-high-rise buildings and large-scale bridges have been constructed in various part of Japan. Structures like these50

tend to resonate with ground motions that have periods exceeding several seconds. There are therefore fears that long-period0

ground motions will affect
A building has its own uniqueperiod when it is particularly
susceptible to shake. If
seismic waves occur near that
period, the building shakes
wildly. This phenomenon iscalled resonance.

−50
0

10

20

30

40

50

60

70

80

90

100
（seconds）

The 2003 Tokachi-oki Earthquake: long-period ground motions were observed inTomakomai City, where the sway continued for nearly 3 minutes.

those structures. On the other
hand, low-rise buildings tendresonate with short-period
ground motions.

*In the figure, a part exceeding 100 seconds is cut off.

(Data taken from the Japan Meteorological Agency website)

14

Short-period seismic motion

Long-period seismic motion

15

are the hypocenter, epicenter
Q11 Whatand hypocentral areas?
The point where the fracture started is called the hypocenter. An epicenter is the point on the groundsurface directly above the hypocenter. Hypocentral regions are regions where fractures have spread
due to faulting.
Enormous forces are acting on the underground rock masses. When the forces become too great for the rock masses to bear,
they fracture. This induces an earthquake. A hypocenter is the point where the fracturing has started. An epicenter is the pointon the ground surface directly above the hypocenter. The fracture, which started at the hypocenter, spreads to the surrounding
region and stops at a certain distance. This expanded region is called the hypocentral region. It is in this region that the vastenergy of earthquakes is generated.

seismic intensity and earthquake
Q12 Aremagnitude different?
Intensity is the greatness of the shake observed at the location and earthquake magnitude is thegreatness of the earthquake itself.
Intensity is a measure of the shake at a particular location. When an earthquake occurs, the seismic waves propagate in every
direction. Since the behavior of the wave propagation differs depending on the distance from the hypocenter and groundcondition, the strength of shake differs with location. The strength is measured at various locations to define the intensity ateach place.
Earthquake magnitude, on the other hand, is a measure of how great the actual fault movement that occurred at a
hypocentral region is. The scale of an earthquake (earthquake magnitude) depends on the size of the fault plane and amount of
displacement. By using the maximum amplitude on equipment such as a seismograph, earthquake magnitude can be seen as anindirect expression of the energy unleashed by seismic waves caused as a result of faulting.
Intensity 2

Epicenter

Intensity 4

Intensity 5 lower

Intensity 6 upper

Sedimentarylayer(soft ground)

Hypocentral
regionHypocenter(Slightly hardground)Rock mass (hard)

Earthquake magnitude 7.0

Pattern diagram showing the relation between
hypocenters, epicenters and hypocentral regions

Earthquake magnitude, which represents the scale of faulting, only provides one
reading for earthquakes. However, the intensity, which represents the strengthof shake at different locations, varies with the location. The figure shows thatshake movements are larger when the hypocenter is nearer and the ground issofter.

35°
N

Hypocentral region
Epicenter

0

1

2

3

Imperceptible topeople.

Felt slightly by somepeople keeping quiet
in buildings.

Felt by many people
keeping quiet inbuildings.

Felt by most people
in buildings.

4

5 lower

HimejiAkashi

34°
40'N

Kobe

Nishinomiya
Osaka

Hokudan
34°
30'N

34°
20'N
0

5km

5 upper

6 lower

6 upper

Epicenter of the 1995 Hyogoken-nanbu Earthquake (M7.3)
and ground surface projection of its hypocentral region- Most people are startled.
- Hanging objects such as
lamps swing significantly.
- Unstable ornaments
may fall.

- Many people are frightened
and feel the need to hold onto
something stable.
- Dishes in cupboards anditems on bookshelves may fall.
- Unsecured furniture may
move, and unstable furniture
may topple over.

7

Sumoto134°
30'E 134°
40'E 134°
50'E 135°
0'E 135°
10'E 135°
20'E 135°
30'E

16(hypocentral region)

Hypocenter

Earthquake source fault

34°
50'N

Earthquake
source fault

High earthquake Low earthquake
resistanceresistance- Many people find it
difficult to walk without
holding onto something
stable.
- Dishes in cupboards anditems on bookshelves are
more likely to fall.
- Unsecured furniture may
topple over.
- Unreinforced
concrete-block walls
may collapse.

- It is difficult to remain standing.
- Many unsecured furniture moves
and may topple over. Doors may
become wedged shut.
- Wall tiles and windows may
sustain damage and fall.
- In wooden houses with low
earthquake resistance, tiles may
fall and buildings may lean orcollapse.

High earthquake Low earthquake
resistanceresistance- It is impossible to move without
crawling. People may be thrownthrough the air.
High earthquake resistance Low earthquake resistance- Most unsecured furniture moves,and is more likely to topple over.
- Wooden houses with low earthquake resistance- Wooden houses with low
are even more likely to lean or collapse.
earthquake resistance are more
- Wooden houses with high earthquake resistancelikely to lean or collapse.
- Large cracks may form, and large may lean in some cases.
- Reinforced-concrete buildings with low earthquake
landslides and massif collapses
resistance are more likely to collapse.
may be seen.

17

Q13 What are“main shocks”and“aftershocks”?

Q14 What are “earthquake swarms”?

A main shock is the largest earthquake in a sequence. Smaller earthquakes that repeatedly occur
afterward are aftershocks.

Earthquake swarms are sequences of earthquakes in which similar size earthquakes occur in a
relatively small area in a concentrated manner.

When large earthquakes occur, many small earthquakes often occur afterward. The largest earthquake is called the main

Sometimes similar size earthquakes occur in a concentrated manner in a relatively small area. This happens for a certain

shock and the subsequent smaller earthquakes are called aftershocks.

period of time and then they calm down. Such earthquakes are called earthquake swarms. What makes earthquake swarms

The magnitude of aftershocks varies but the largest of them is called the largest aftershock. Generally the magnitude of thelargest aftershock is smaller by 1 or more than the main shock. It is known that aftershocks frequently occur immediately after
the main shock. However, their rate declines as time elapses. It is also known that if the magnitude of the main shock is large, ittakes a longer amount of time for the aftershocks to die down.

distinctive is that they occur many times, their hypocenters are shallow, and they are quite small. However, sometimes
medium-sized earthquake swarms with magnitudes of 5 to 6 occur.
The 1965 Matsushiro Earthquake Swarm, the 1978 Izu Hanto Toho-oki Earthquake Swarm, and the 2000 Izu Shoto
Earthquake Swarm are famous in Japan. It is assumed that earthquake swarms are somehow related to the undergroundmovement of fluids, such as magma. It is assumed from crustal deformation data that the 2000 Izu Shoto Earthquake Swarm
occurred when plate-shaped magma intruded into the rock mass.

Example of“main shock – aftershock”type earthquake activity(the Iwate-Miyagi Nairiku Earthquake on June 14, 2008)

Example of“swarm type”earthquake activities(The 2000 Izu Shoto Earthquake Swarm)

From Jun. 26, 2000 to Aug. 31, 2000

M

Main shock, 8:43 a.m., June 14, 2008
Magnitude

Magnitude

7

20th

800

600

400

200

June 14th

20th

30th

(Hypocenters with magnitudes of 2.0 or greater, provided by the Japan Meteorological Agency)

18

Jul.9
M6.1

Jul.15
M6.3
Jul.30M6.0

6Jul.30
M6.5

Aug.18
M6.1

7

6

5

5

4

4

3

3

Jun.2630th

Number of earthquakes per day

Number of earthquakes per day

June 14th

Jul.1
M6.4

Jul.1

Jul.15Aug.1

Aug.15

Aug.31

Jul.1

Jul.15Aug.1

Aug.15

Aug.31

400

300

200

100

Jun.26(Hypocenters with a magnitude of 3 or greater, provided by the Japan Meteorological Agency)

19

Q15 How are tsunamis generated?

Q16 What is “liquefaction”?

If large crustal deformation occurs under the sea as a result of an earthquake, it moves the overlying
mass of seawater and generates a tsunami.

Liquefaction is a phenomenon where, due to the shaking of an earthquake, soil with high watercontent becomes like liquid.

When large earthquakes occur in the ocean, large crustal deformation occurs on the seafloor. Due to the crustal deformation,

Soil on low land or reclaimed land contains a lot of water (pore water). In soil such as this, sandy particles are holding eachthe overlying seawater rises and falls. This fluctuation of seawater creates a tsunami. Tsunamis are generated not only byother together. With their water-filled pores, they stay stable. When a strong shake is applied by an earthquake, this system is

earthquakes under the ocean, but also by submarine volcanic eruptions, seafloor landslides, or large collapses near the shore.

destroyed. When this happens, the water pressure between the sandy particles increases. This turns the ground into a muddy,

Tsunamis characteristically decrease their velocity and increase their height rapidly as they approach land and the depth ofwater-like state. The muddy water tries to support the load from above. However, if there are fissures or weak parts in thethe sea decreases. The velocity, although it may be slower near land, is still nearly 40 km/h in areas where water depth isground surface, the water becomes unable to support the load. This causes muddy water to erupt to the surface. Liquefaction

approximately 10 m. The height of a tsunami doesn’t only depend on how great the earthquake was, but also on thecan cause various types of damage. In addition to ground subsidence, it can cause ground-based tanks or manholes to float, andtopography of the seabed and the geographical shape of the coastline. Tsunamis can become much higher due to the shape of abuildings and other structures to lean or collapse.

particular bay or cape.

1) Before an earthquake
Sand particles Pore waterContinental plate

Continental plate

Oceanic plate
Oceanic plates slowly sink under continental
plate over decades or hundreds of years.
Strain accumulates when the end of acontinental plate is dragged in downward.

Oceanic plate2) During an earthquake

When the strain exceeds a certain
limit, the end of the continental platejumps up (an earthquake occurs).

The sandgushes out

When this happens, large volumes ofseawater rise and fall.

Continental plate

3) After an earthquake
Subsidence

Oceanic plate
A tsunami is generated, which then advances
toward land.

20

21

Q17 Is it possible to predict earthquakes?
Generally speaking, it is difficult to predict the occurrence of earthquakes.

Q18 What is an “earthquake early warning”?
An earthquake early warning is an information announcement about the occurrence of an earthquake
before the actual main shake arrives. The information is obtained from the characteristic seismic waves.

Earthquake prediction means to predict “when, where an earthquake will occur, as well as how big it will be, before its

Seismic waves have P waves (preliminary tremors), which have a large propagating velocity, and S waves (main tremors),

occurrence based on scientific grounds.” Earthquake prediction is generally considered to be difficult with present science andwhich are slower. Damage due to earthquake shaking is mainly caused by the S waves. Real-time analysis of the hypocentertechnology, even if limited to large-scale earthquakes.

location and strength of the earthquake (magnitude) are now possible immediately after the occurrence of an earthquake,

It is thought that a large-scale earthquake could occur at any time in Tokai. This is a conclusion drawn from the history of

thanks to the progress in seismology and information processing technology. This can be done with just the arrival data of P

repeated large earthquakes. About half of the hypocentral regions of past earthquakes were underground and inland. Therefore, itwaves near the hypocenter. Once the hypocenter and the magnitude of the earthquake are determined, it is possible to estimate

is thought that earthquake prediction might be possible by developing highly accurate observation networks for capturing

the seismic intensity at a given location.

earthquake precursors and monitoring the obtained data. Arrangements for monitoring and information sharing are now in place.

This is the system that is currently maintained all over the country to transfer information regarding analyzed and predicted

However, there are still many unknown factors when it comes to the occurrence processes of an earthquake in Tokai. In

hypocenters, earthquake magnitudes and seismic intensity before the arrival of S waves. It is known as the “earthquake earlysome cases, earthquake precursors are too obscure to detect, or even if they are detected there is sometimes no time to releasewarning” system and the information is provided by the Japan Meteorological Agency through formats such as TV. It is

the information before the earthquake occurs. Therefore, preparing measures for disaster prevention is also a necessary step that

expected that disaster prevention organizations, transportation facilities, public facilities, and others will be able to respond tomust be taken to guard against sudden earthquake strikes.

the warning and prevent or minimize the earthquake damages before the S waves arrive. However, if the hypocenter is close, it
becomes impossible to cope with the S waves before they arrive. It is therefore important to keep the differences between P
waves and S waves in mind.

)

35˚

S

es
av
w

in
ma

(

rs
mo

tre

P

s
ve
a
w

r

ina

im
rel

(p

rs)

mo

re
yt

Information issent to residents

Japan Meteorological Agency

34˚uEarthqReal-time
data transfer

Seismometer

arly
ake e

g

warninNews media,
disaster prevention
organizations, etc.

As soon as an earthquake (P waves) is detected near the

138˚

139˚

Volumetric strainmeter

Seismometer

Tidal gauge

Multi-component strainmeter

Ocean bottom seismometer

Groundwater observatory

Volumeric strainmeter placedin Izu area

Extensometer

GNSS

Tiltmeter

Anticipated hypocentral
region of an earthquake in Tokai

Strainmeter placedin other institutions

Anticipated hypocentral region of an earthquake in Tokai and the crustal
deformation observation network (Figure from the Japan Meteorological Agency website)Anearthquake

0 sec

Few seconds
later

Announcement of information

137˚

P waves (preliminary tremors) observed

hypocenter, the process to send the earthquake early warning
begins. It becomes a ﬁght against time with seismic waves.

5 sec

10 sec15 secLead time from the announcement of information until the main tremors

The further from the hypocenter, the bigger the lead time is.

・ The earthquake early warning system catches earthquakes (P waves and preliminary tremors) near their
hypocenter and automatically calculates their location, magnitude, and estimated seismic intensity. The result
is notified swiftly, ranging from several seconds to several dozen seconds, before the strong shaking (Swaves and main tremors) arrives.
・ However, for locations near the hypocenter, sometimes there is no warning time to prepare for strong shaking.
(Taken from a leaflet published by the Japan Meteorological Agency)

22

23

Supporting Section

Applying the Outcome of Investigative Earthquake Research for Disaster Prevention

Supporting Section

Part 1 Government Efforts

Ⅰ . General Overview of the Headquarters for Earthquake Research Promotion
The Great Hanshin-Awaji Earthquake Disaster on January 17, 1995 killed 6,434 people and destroyed over 100,000 buildings. This was
the worst damage that Japan had suffered since the end of World War II. It also brought to light a number of problems in the national
earthquake disaster prevention measures at the time.
Based on these problems, the Special Measure Law on Earthquake Disaster Prevention was enacted by legislators in July 1995. It was
designed to promote a comprehensive national policy on earthquake disaster prevention.
The law recognized that the national system had failed to sufficiently communicate and apply the results of earthquake research togeneral public and disaster prevention organizations. As a result, the Headquarters for Earthquake Research Promotion was established inaccordance with this law as a special governmental organization attached to the Prime Minister’s Office (it now belongs to the Ministry of
Education, Culture, Sports, Science and Technology). It was established in order to clarify the systems of responsibility regarding

Supporting Section□ Basic objectives
To promote research of earthquakes in order to strengthen earthquake disaster prevention measures,
especially for the reduction of damages from earthquake.

□ Roles
1. Planning of comprehensive and basic policies
2. Coordination of budgets and other administrative work with related governmental organizations
3. Establishment of comprehensive survey and observation plans
4. Collection, arrangement, analyses, and comprehensive evaluation of survey resultsby related governmental organizations, universities, etc.
5. Publication based on the above evaluations

2. Composition of the Headquarters for Earthquake Research Promotion
The Headquarters for Earthquake Research Promotion consists of a director (the Minister of Education, Culture, Sports, Science

Part 2

Applying the Outcome of Investigative Earthquake Research for Disaster Prevention
Ⅰ . Long-term Evaluation
The Headquarters for Earthquake Research Promotion is evaluating earthquakes along the main active faults of Japan, as
well as and subduction zone earthquakes. It is doing this to estimate the magnitudes of possible earthquakes and theprobabilities of them occurring in given periods. The Headquarters refers to this practice as “long-term evaluation.”
In long-term evaluation, you can see the “places” where large-scale earthquakes might occur, as well as their their specific“scale (earthquake magnitude)” and “probability” of occurrence.
■ The results of long-term evaluation along the main active fault zones

Legend:earthquake research that is directly connected to government policy. It manages this in an integrated fashion with a governmental capacity.

1. The basic objectives and roles of the Headquarters for Earthquake Research Promotion

Kushigata-sanmyaku (Kushigata
Mountains) Fault Zone
M6.8 class, ranges from 0.3% to 5%
Atera Fault Zone
Main part: northern segment
M6.9 class, ranges from 6% to 11%

Yamagata-bonchi (Yamagata basin)
Fault Zone
Northern segment
M7.3 class, ranges from 0.003% to8%Biwako-Seigan (west bank of Biwa
Lake) Fault Zone Northern segment
M7.1 class, ranges from 1% to 3%
Chuo-Kozosen (Japan Median TectonicLine) Fault Zone Kongo-sanchi-toen(eastern edge of the Kongo Mountains)
M6.9 class, nearly 0% to 5%

Sarobetsu Fault Zone
M7.6 class, less or equal to4%
Shonai-heiya-toen(eastern edge of
Shonai plain) Fault
Zone
Southern segment
M6.9 class, ranges
from nearly 0% to 6%
Shinjo-bonchi(Shinjo basin) Fault
Zone
Eastern segment
M7.1 class, less orequal to 5%

Chuo-Kozosen (Japan Median Tectonic Line)
Fault Zone Izumi-Sanmyaku-Nan-En (Southernedge of Izumi Mountains) Ranges from about
M7.6 to 7.7, ranges from about 0.06% to 14%
Akinada (Aki-nada Sea) Fault Zone
Main part M7.0 class, ranges from
0.1% to 10%
Hinagu Fault Zone
Yatsushirokai (Yatsushiro-kai Sea)
segment Ranges from about 7.3 class,ranges from nearly 0% to 16%
Hinagu segment M7.5 class, ranges
from nearly 0% to 6%

Collaboration- Central Disaster Management Council- Subdivision on Geodesy and Geophysics,
Council for Science and Technology- Coordinating Committee for Earthquake Prediction- Assessment Committee for Areas under Intensified
Measures against Earthquake Disaster

The Headquarters for Earthquake Research Promotion(Director: Minister of Education, Culture,
Sports, Science and Technology)

Policy Committee

Earthquake Research Committee

Survey and Observation Data,
Research Results
Japan Meteorological
AgencySurvey, Observations, Research, etc.
MEXI

GSI

JMA

JCG

Various
universities

NIED

JAMSTEC

AIST

NICT

NRIFD

MEXI:
GSI:
JMA:
JCG:
NIED:
JAMSTEC:
AIST:
NICT:
NRIFD:

24

Ministry of Education, Culture, Sports, Science and Technology
Geospatial Information Authority of Japan
Japan Meteorological Agency
Japan Coast Guard
National Research Institute for Earth Science and Disaster Prevention
Japan Agency for Marine-Earth Science and Technology
National Institute of Advanced Industrial Science and Technology
National Institute of Information and Communications Technology
National Research Institute of Fire and Disaster

Takayama-Oppara Fault Zone
Kokufu Fault Zone
M7.2 class, ranges from nearly
0% to 5%matters such as evaluation-based publications.

Itoigawa-Shizuoka-Kozosen(Itoigawa-Shizuoka Tectonic Line) Fault
Zone (Segment including the Gofukuji
Fault)
M8 class (ranges from 71/2 to 81/2), 14%

The "Earthquake Research Committee" holds regular meetings
on a monthly basis and classifies and analyzes research andto evaluate seismic activity in a comprehensive manner and to
publish evaluation results. In addition, ad hoc meetings are held

Comprehensive Basic Policies
Survey and Observation Plans

Morimoto-Togashi Fault Zone
M7.2 class, ranges from 2%
to 8%

coordinates budgets and other administrative work and deals withobservation results, as well as study outcomes. It does this in orderin response to damaging earthquakes or marked seismic activity.
The meeting seeks to assess the current activity and the probabilityof aftershocks.
The Headquarters for Earthquake Research Promotion
formulated its new policy, which was titled: “New Promotion ofEarthquake Research - Comprehensive Basic Policies for the
Promotion of Seismic Research through the Observation,
Measurement, and Survey -.” This policy is a guideline ofearthquake research for the next 10 years, and was released in2009 (revised in September 2012).

Tonami-heiya (Tonami plain) /Kurehayama
Fault Zone
Tonami-heiya (Tonami plain) Fault Zone
(eastern segment)
M7.0 class, ranges from 0.04% to 6%
Kurehayama Fault Zone
M7.2 class, ranges from nearly 0% to 5%

Tokamachi Fault Zone
Western segment
M7.4 class, 3.0 or more

Okinawa

policy concerning the promotion of earthquake research. It also

Kuromatunai-teichi (Kuromatsunai
lowland) Fault Zone M7.3 class andover, less or equal to 2% to 5%

Takada-heiya (Takada plain) Fault Zone
Takada-heiya-toen (eastern edge of
Takada plain) Fault Zone
M7.2 class, ranges from nearly 0% to 8%

Committee” and the “Earthquake Research Committee,” composed of staff from related government offices and academia.
The “Policy Committee” implements the planning of basic

As of Jan.15, 2014

High (Probability of occurrence within 30 years is 3% or larger)
Name of the fault zone
Slightly high (Probability of occurrence within 30 years ranges Kannawa/Kouzu-Matsuda Fault Zone
Earthquake occurrence“Nearly 0%” represents
M7.5 class, ranges from 0.2% to 16%
from 0.1% to 3%)
probability within 30 years less than 0.001%
No notation (Probability of occurrence within 30 years is lessScale of earthquake
Earthquake occurrence probability isthan 0.1%, or the probability is unknown, or it has been(earthquake magnitude) calculated for January 1, 2014
evaluated to not be an active fault)

and Technology) and staff members (such as the vice ministers of related ministries and agencies). Underneath them are the “Policy

Disaster prevention measuresat national and regional levels

Part 2

Kego Fault Zone
Southeasternsegment
M7.2 class,ranges from 0.3%
to 6%
Unzen Fault GroupSouthwestern part: northern segment
M7.3 class, ranges from nearly 0%
to 4%
Beppu-Haneyama Fault Zone
Ooita-heiya(Oita plain)—Yufuin Fault
Zone/western segment
M6.7 class, ranges from 2% to 4%
Ooita-heiya (Oita plain)—Yufuin Fault
Zone/eastern segment
M7.2 class, ranges from 0.03% to 4%

Rokko-Awajishima (Awaji
Island) Fault Zone
Activated in the Great
Hanshin-Awaji Earthquake
Disaster (Hyogoken-nanbu
Earthquake)
Main part: Awajishima-Seigan(west coast of Awaji Island)
segment including the Nojima
Fault
Probability immediately before
the occurrence of theearthquake
M7.3, ranges from 0.02% to 8%
Suonada (Suo-nada Sea) Fault
Group
Main partM7.6 class, ranges from 2% to 4%

Sakaitoge-Kamiya Fault Zone
Main partM7.6 class, ranges from 0.02% to13%
Kiso-Sanmyaku-Seien (westernedge of Kiso Mountains) Fault Zone
Main part: southern segment
M6.3 class, ranges from nearly 0%
to 4%
Nara-bonchi-toen (eastern edge of Narabasin) Fault Zone
M7.4 class, ranges from nearly 0% to 5%
Uemachi Fault Zone
M7.5 class, ranges from 2% to3%Miura-Hanto (Miura Peninsula) Fault Group
Main part/Takeyama Fault Zone
M6.6 class (possibly greater or equal to6.6), 6% to 11%
Main part/Kinugasa/Kitatake Fault Zone
M6.7 class (possibly greater or equal to6.7), ranges from nearly 0 to 3%
Kannawa/Kouzu-Matsuda Fault Zone
M7.5 class, ranges from 0.2% to16%
Fujikawa-Kako Fault Zone
(Case a)M8.0 class, ranges from 10% to 18%(Case b)M8.0 class, less or equal to 2% to 11%”Occurrence probability”of earthquake
Earthquakes are generated by dislocation on a fault. It is thought that individual faults have their own
individual recurrence intervals. If the recurrence interval and the time of the previous earthquake are known,
the time of the next earthquake can be estimated to a certain extent. However, since the actual recurrence
interval can vary and is sometimes uncertain, the time of the next earthquake is expressed as a probability.

25

Supporting Section

Applying the Outcome of Investigative Earthquake Research for Disaster Prevention● The probability of earthquake occurrence and the probability of other accidents or disastrous events
The probability of earthquake occurrence given in the figure is usually only a few percent. This might seem small, but thisvalue does not mean that we are free from earthquakes and are safe.
For example, the probability of getting killed in a traffic accident within 30 years is approximately 0.2%*1. If you compare
this value with that of an earthquake, you can see that the probability of earthquake occurrence is not so small. Furthermore,an earthquake can, even if the occurrence probability is low, inflict enormous damages once it occurs. It is important toconsider its possible extent of damages when accepting this probability.
＊ 1 Calculated based on the statistics from the White Paper published by the Fire and Disaster Management Agency, using a specific assumption.

■ Results of long-term evaluations of Subduction zone earthquakes(off the shore of Akita Prefecture)
M7.5 class, about 3% and less

Region nameEarthquake occurrence
probability within 30 years
Scale of earthquake(earthquake magnitude)
Earthquake occurrence probability is calculated for January 1, 2014

Northwestern Hokkaido-oki(off the shore of northwestern
Hokkaido)
M7.8 class, ranges from0.006 to 0.1%

Nemuro-oki (off the shore of Nemuro)M7.9 class, about 50%
Simultaneous occurrence with
Tokachi-oki
M8.3 class

The Chishima
Trench(Kuril Trench)
Tokachi-oki (off the shoreof Tokachi)
M8.1 class
Ranges from 0.9% to 4%
Simultaneous occurrencewith Nemuro-oki
M8.3 class

The Nansei-shoto
Trench(Ryukyu Trench)

Inter-plate earthquakes inHyuga-nada
Around M7.6, about 10%

The Headquarters for Earthquake Research Promotion made the “National Seismic Hazard Maps for Japan” public in 2005.
Since then it has been publishing seismic hazard maps that reflect the latest information.
There are two types of seismic hazard maps, which have different perspectives. The first of these is the “Probabilistic Seismic
Hazard Maps,” which shows the probability of strong shakes occurring at given areas over designated periods. The second is the“Seismic Hazard Maps for Specified Seismic Source Faults,” which shows specified faults and how strongly certain areas near
the faults can shake if an earthquake were to occur at those faults. Seismic hazard maps are prepared based on long-term
evaluations. These are predictions of earthquake magnitudes and the probability of earthquake occurrence in a given period.
based on seismic ground motion prediction methods, which specify earthquake source faults.

The 2003 Tokachi-oki Earthquake

Inter-plate earthquakes in
Aki-nada, Iyo-nada, andBungo-suido
Ranges from M6.7 to 7.4, about
40%

II. Seismic Hazard Maps

They target earthquakes that occur at main active faults, as well as subduction-zone earthquakes. Seismic hazard maps are also

As of Jan.15, 2014

Legend: Akita-ken-oki

Akita-ken-oki(off the shore of
Akita prefecture)
M7.5 class
About 3% and lessEastern margin of
the Sea of Japan
Northern Sadogashimaoki (off the northernshore of Sadogashimaisland)M7.8 class
Ranges from 3% to 6%

The Japan
Trench

M8.0 About 60%*
*The probability immediately before the occurrence of the earthquake.
This is the first case inwhich an earthquake thatwas expected to occur inthe Headquarters for
Earthquake Research
Promotion’s earthquake
occurrence long-term
evaluation actuallyoccurred.

Northern Sanriku-oki (off the northernshore of Sanriku)
M8.0 class, Mt8.2 class (*1)
Ranges from 1% to 20%(Earthquakes other than those that haverepeatedly occurred)
Ranges from M7.1 to 7.6, about 90%

Since these two maps have different perspectives, you must properly choose which should be used depending on yourpurpose or interest in preparing for future earthquakes.
Basic use of seismic hazard maps
○ Probabilistic Seismic Hazard Maps
With this map you can find out how high and how regionallydifferent the probability of strong shaking occurrences are over acertain period. You can also consider all the possible
earthquakes that will influence a particular area of interest.

○Seismic Hazard Maps for Specified Seismic Source Faults
With this map you can see how severe the groundmotion would be in particular areas around aparticular seismic source fault if an earthquake
occurred.

■ A diagram showing the probability distribution of a shaking with■E
 valuation of a strong ground motion, assuming

intensity 6 or greater hitting within 30 years (Base date: Jan.1, 2013)
Probability
26% or greater
High
Ranges from 6% to 26%
Ranges from 3% to 6%
Slightly
Ranges from 0.1% to 3%
high
Smaller than 0.1%

that an earthquake occurs along an active fault

Evaluation of a strong ground motion, assuming that the earthquake
occurs along the Kego Fault Zone (south-eastern segment)(made public in April 2008)
Kitakyushu(*1) Mt: Scale of an earthquake measured by tsunami height
Miyagi-ken-oki (off the shore of Miyagi
Prefecture)
M7.4 class, occurrence probability unknown(Earthquakes other than those that haverepeatedly occurred)
Ranges from M7.0 to 7.3, about 60%

Fukuoka

Close to the trench in Southern
Sanriku-oki
M7.9 class, nearly 0%(Earthquakes other than those thathave repeatedly occurred)
Ranges from M7.2 to 7.6, about 50%

Earthquakes somewhere on
the Nankai TroughRanges from M8 to M9 class
About 70%

Along the Sagami Trough(Earthquakes like the 1923
Great Kanto Earthquake)M7.9 class
Ranges from nearly 0% to2%26Part 2

Earthquakes like the off the Pacific
Coast of Tohoku Earthquake
Ranges from Mw8.4 to 9.0
Nearly 0%

Other earthquakes in
Minami-Kanto (southern
Kanto area) of about M7
Ranges from M6.7 to 7.2
class
About 70%

Northern Sanriku-oki to Boso-oki
along the Japan Trench
Tsunami earthquakes
Ranges from Mt8.6 to 9.0
About 30%
(About 7% for specific regions)
Normal fault type
M8.2 class, Mt8.3 class
Ranges from 4% to 7%(Ranges from 1 to 2% for specificregions)
Fukushima-ken-oki (off the shore of
Fukushima Prefecture)
M7.4 class (Multiple earthquakes occur insuccession)
About 10%
Ibaraki-ken-oki (off the shore Ibaraki
Prefecture)
Ranges from M6.9 to 7.6, about 70%(Inter-plate earthquakes that occur
repeatedly)
Ranges from M6.7 to 7.2
About 90% (probably larger)

Saga

Seismic intensity

Revisions for the seismic hazard map are currently being undertaken.

5.05 upper5.56 lower6.06 upper and over
0 0.5 1 1.5 2 2.5 3 3.5 4 4.55 lower

Please keep in mind that the seismic hazard map in this material,
including the above diagram, is in the process of revision.

Utilization of the“Seismic Hazard Map”
The“Probabilistic Seismic Hazard Map”and“Seismic Hazard Maps for Specified Seismic Source Faults”are prepared by the Earthquake
Research Committee. They are not only used to raise awareness about seismic disaster prevention; they also fulfil the following roles:
Earthquake-related survey and observation

Regional inhabitants

Basic materials for selecting areas to be highlighted
for earthquake-related survey and observation.

Raising of awareness of the local residents
concerning earthquake disaster prevention.

Earthquake disaster prevention measures

Risk evaluation

Basic materials for drawing up land utilization plans, seismic designs for facilities or
structures. Basic materials for the planning of regional disaster prevention schemes.

Basic materials for risk evaluation, such as locating important facilities,
deciding new business locations, or evaluating of insurance rates.

27

Supporting Section

Applying the Outcome of Investigative Earthquake Research for Disaster Prevention

Part 2

Probabilistic Seismic Hazard Maps

Seismic Hazard Maps for Specified Seismic Source Faults

The Probabilistic Seismic Hazard Maps indicate the “possibilities of strong shaking within a certain period at every location

The Seismic Hazard Maps for Specified Seismic Source Faults focuses on specific earthquake source faults. They show theon the map.”shaking intensity of the areas around the faults when the earthquakes occur. For example, they are useful for checking how

In preparing this map, all earthquakes that might influence a particular area have been considered. The consideredstrong the shaking will be if an earthquake occur at a fault near you. These kinds of maps have been provided and widely

earthquakes in these maps consist of not only earthquakes that have already been through long-term evaluation, but alsoutilized for estimating damages and drawing up national or regional disaster mitigation plans. To ensure that any user canearthquakes that are difficult to find source faults for before they occur. This includes earthquakes that occur in an area whereobtain the same predicted results, the Earthquake Research Committee has been working toward standardization of the strongno active fault has yet been found.

ground motion prediction method and has formulated the “Recipe for Predicting Strong Ground Motion for Specified Seismic

For the probabilistic seismic hazard maps, three quantities are used. These are the “time span,” “intensity of shakes,” andSource Faults”. At the same time, the committee has been conducting estimations of how strong shaking would be and has“probability.” To present the maps, a convention was adopted so that two of the quantities were fixed to show the distribution

been making a series of seismic hazard maps publics for specified seismic source faults. For the evaluation, the committee hasof the remaining quantity. For example, below is a distribution map of “probability,” that is shown with the “time period” andbeen selecting earthquakes that may have large impacts on their surrounding areas, out of those that may occur at active faults“intensity of ground motion” fixed. Reports on the Probabilistic Seismic Hazard Map are publicly available on theor subduction-zones. Seismic hazard maps for specified seismic source faults are openly available on the Headquarters for

Headquarters for Earthquake Research Promotion’s website.

Earthquake Research Promotion’s website.

Seismic hazard maps can also be seen on the website of the National Research Institute for Earth Science and Disaster
Prevention (NIED), “Japan Seismic Hazard Information Station (J-SHIS).” You can zoom-in on the map, find out “theCase 1aCase 1bCase 2aCase 2b

probability of ground motion equal to or larger than seismic intensities of 6 lower, occurring within 30 years from thepresent,” or the “ground susceptibility to shaking.” You can also check the main active faults or the hypocentral regions of
subduction zone earthquakes. Seismic hazard maps are revised every year.

■ Probabilistic Seismic Hazard Maps
A distribution map with of the probability of ground motions equal to or larger than seismic intensity of 6
lower, occurring within 30 years into the future (Base date: January 1, 2013)

Probability
26% or greater
High
Ranges from 6% to 26%
Ranges from 3% to 6%
Slightly
Ranges from 0.1% to 3%
high
Smaller than 0.1%

■ S eismic Hazard Maps
for Specified Seismic
Source Faults
Strong ground motion
evaluation, assuming theearthquake occurs along
the Kego Fault Zone
(southeastern segment)

０

１Earthquake source fault modelNorthwest

Assumed
fault
plane

２

３

４

Intensity

Southeast

Asperity(12 km x 8 km)

Asperity (an area where the amount of sliding is predominant
and the seismic waves generated are strongest)
Revisions for the seismic hazard map are currently being undertaken.
Please keep in mind that the seismic hazard map in this material,
including the above diagram, is in the process of revision.

28

５ lower ５upper ６lower ６upper and larger

Northwest

Southeast

Secondasperity(6 km x 6 km)

Surfacetrace of a
fault

First
asperity(8 km x 8 km)

Rupture initiation point

Two cases having one asperity (Case 1a and Case 1b) and two cases having two diﬀerent-sizedasperities (Case 2a and Case 2b) have been assumed. The rupture initiation point was thelowest point of either the northwestern end or the southeastern end.
(1a, 1b, 2a, and 2b are the rupture initiation points. They are also the case names.)29

Supplementary Material Section

Measures you can take to stay safe from earthquakes
Ⅰ . Before an earthquake occurs:
Earthquakes can hit suddenly. It is important to always be as prepared as you possibly can.
Protect Yourself

      

Keep furniture fromfalling or moving.
・Set furniture inplaces so as not tocause injuries or
hamper your escape.
・Secure the furniture,
TV or personal
computers in place.
Keep them fromfalling or moving
with a quake.

Be Prepared andReady to Act

Always be ready to
extinguish fires.
firefighting―with children safely kept off.

Confirm the strength ofyour house and walls.

・Take measures to keep cupboard andwindow glass from shattering andscattering.
・Keep a flashlight handy in case of power
failure.
・Have slippers or sneakers on hand; they
can protect you from shattered glass orothers.

・Have your home inspected for earthquake
safety and reinforced if necessary.
・Reinforce concrete and block walls so they
won’t collapse.

Take steps for fire prevention
and early detection.

・Keep a fire extinguisher within easy reach.
Also, keep water in the bathtub for

Be prepared to
avoid injuries.

Prepare emergency
supplies in advance.
・Know where your emergency supplies are.

・Install fire alarms in your homefor early warning.
・Keep electrical appliances
unplugged when not in use.
・To prevent electric or gas fires,
install circuit breakers or outlets
with a seismic shut-off function.

・Plan how to utilize ordinary items such as car
jacks and radios in an emergency.

Train yourself foremergencies.

Keep Calm andAct Well

Meet with your family to
discuss what you would do.

Know potential
hazards in your area.

Keep informed
about disasters.

・Decide each family member’s role in case ofan earthquake : fire prevention, initial firefighting, and other tasks.
・Make sure your family knows how to contact
and where to reunite when you cannot
return home or are separate after a quake.

・Keep informed how your area canbe dangerous with the local
hazard map.
・Walk around your school/officearea to see what can pose dangers
or help you in an emergency.
Then prepare your own safetymap.

・Keep yourself informed about
disasters via newspapers, television,
radio and the Internet.
・Attend meetings and classes at firestations to learn lessons from pastearthquakes.

・Confirm evacuation sites
and routes as a family.
・Discuss with your family
how to prepare tocooperate you’re yourneighbors.

・Participate in disaster drills. Learn
skills for self protection, fire prevention,
fire fighting, rescue, first aid,
emergency reporting, evacuation, andothers.

(Provided by the Tokyo Fire Department)

Ⅱ .  If an earthquake occurs:
In order to stay safe from earthquakes, it is important to know and think about what to do in advance. If there is ever atsunami threat, evacuate at once. When doing so, keep the preparations shown on the following page in mind.
When You Feel A Quake Or Hear The Emergency Earthquake Warning...

QUAKE! Protect Yourself First.
・Be prepared and protect yourself from an earthquake when you hear an earthquake warning
announcement or feel a quake.
・Stay under a large table until a quake is gone.

Keep yourself safe fromfalling or moving objects during a quake.
【High-rise Building with 10 or More Floors】
・Upper floors may be shaken for several minutes.
・Large, slow shakes may let the furniture fall down or move across the

Right After An Earthquake

room.

Keep Calm. Check All Fire
Sources. Put Out Fire Quickly.

Keep Calm. Panic May
Cause You Injuries.

Make Sure You Have Ways
Out: Open Doors And Windows.

Keep Away From Gateposts
And Walls.

・If you were using any sources offire or heat, turn them off when
the shaking calms down.
・If a fire starts, put it out quickly
and calmly .

・Be careful of fallen objects or
shattered glass in the home.
・Stay inside. Roof tiles, broken
window glass or signboards
may fall down and hit you.

Secure an exit for escape when
the shaking stops.

If you feel an earthquake outside,stay away from concrete walls
and other objects which may fallover.

Get The Right Information.
Take The Right Action.

Make Sure Your Family And
Neighbors Are Safe.

Work Together On Rescue
And First Aid.

Make Sure Electricity And Gas
Are Off Before Evacuation.

Get accurate information fromradio, television, fire stations,
local authorities, etc.

After you confirm your family’s
safety, check if your neighbors
are all right.

Work with your neighbors to freevictims from under debris or
fallen furniture and to give firstaid.

Turn off circuit breakers and thegas at the main before you
evacuate.

After An Earthquake
Stay Away From Fires And Tsunami.
・Take refuge in a temporary assembly spotor an evacuation area when a fire may
threaten your life in the community.
・Leave the coast as soon as possible for ahigher, safer place when you are hit by a
big quake or hear a tsunami warning at
the seaside.

(Provided by the Tokyo Fire Department)

30

U
E

The Earthquake and Disaster-Reduction Research Division,
Research and Development Bureau, Ministry of Education,
Culture, Sports, Science and Technology(Secretariat Division of the Headquarters for Earthquake Research Promotion)
100-8959

3-2-2 Kasumigaseki, Chiyoda-ku, Tokyo

Tel: 03-5253-4111 (switchboard)

E-mail: jishin@mext.go.jp

URL: http://www.jishin.go.jp/en/
Word to search: headquarters for earthquake
headquarters for earthquake

検索

この冊子に掲載している地震動予測地図について、この地図の作成に当たっては、国土地理院長の承認を得て、同院発行の数値地図 25000（空間データ基盤）及び基盤地図情報を使用した。
（承認番号

平 25 情使、第 707 号）

March 2014

T
E