Journal of Natural Disaster Science, Volume 24, Number 1, 2002, pp35-42

Instantaneous Instrumental Seismic Intensity and Evacuation
Yasuko KUWATA 1) and Shiro TAKADA 2)
Graduate School of Science and Technology, Kobe University2)
Dept. of Architecture and Civil Engineering, Kobe University

1)(Received for 29. Jul., 2002)

ABSTRACTThe earthquake that occurred on October 6, 2000 in western Tottori, Japan is an interesting event because residents living in houses that completely collapsed had time to evacuate. The period which people had time toescape from collapsing buildings was due to the particular aspect of ground shaking. Escape time is anotherimportant variable besides building resistance, indoor environment, hour of the day, type of human activity at thetime of the earthquake, that must be taken into account. To measure this new variable, a measure and a modelthat indicate the time available for evacuation are proposed. The measure of transitional characteristics of groundmotion is presented as Instantaneous Instrumental Seismic Intensity (IISI). The duration of ground motion ismodeled for several periods, which characterize human behavior and the surrounding situation. The evacuation
time available defined as the period from when people start to feel the shaking until they cannot move at all, ismeasured by the IISI. An application that indicates the threshold of the time available to evacuate is examined
together with the hypocentral distance and the earthquake s magnitude for practical future use.

1. INTRODUCTION
Seismic physical impacts on people are explained by a combination of ground failure factors (e.g., ground rupture, landslides,
and liquefaction), structural damage factors (e.g., damage to residences, commercial buildings, and transportation systems), andfunctional factors (e.g., human occupancy, human activity, and theindoor environment). Past studies of earthquake-related casualties
have mainly focused on physical damage factors, especially housecollapse. The collapses of vulnerable houses do in fact cause alarge number of human fatalities and injuries. After the 1995
Hyogoken nambu earthquake (MJMA7.2, Mw6.9), which resulted in
6,432 fatalities, several detailed studies have been made of theclasses and levels of damage suffered in order to clarify the relationship between house damage and casualties (e.g., Nishimura etal., 1996). Only a few studies, however, have focused on the characteristics of ground motion. Common parameters of groundmotion used in earthquake-related casualty estimations are thepeak ground acceleration, peak ground velocity, seismic intensity,and SI value. Some studies have investigated the correlation
between the peak ground acceleration and number of casualties(Lu and Miyano, 1995) and between seismic intensity and humanbehavior. Okada (1996), focusing on the time history of groundmotion, showed in detail changes in both household and humanbehavior.
Characteristics of ground motion greatly affect evacuation
behavior and loss of human life during earthquakes. Previous casestudies on earthquake-related casualties, such as the Hyogoken
nambu (Imiya and Ohta, 2000) and Chi-Chi, Taiwan (Kuwata and
Takada, 2001) earthquakes, have noted that human behavior andsurrounding situation during ground shaking are crucial factors inthe saving of human life. As background for our present paper, we
report a site survey of casualties suffered during the 2000 Western
Tottori, Japan earthquake. This is a particularly interesting case as
no human lives were lost occurred despite the collapse of many
houses. Overall damage was only slightly less than in the
Hyogoken nambu earthquake, but this earthquake showed something novel. The intensity of ground motion changed in the shortperiod of the earthquake, and this affected human behavior. All
the case studies cited above provided precious descriptions basedon interviews and questionnaire answers given by inhabitants,
showing remarkable, although non-analytical, trends in cause andconsequence.
Past studies of ground motion and casualties were done in oneof two ways; analyses of peak ground acceleration or qualitative
characterization of various causes. Advances in this type of
research needs to take into account other parameters involved,
from the peak point to the duration of ground motion. The transitional characteristics of ground motion need to be examined inorder to assess human behavior and surrounding conditions morein detail. Two complicated problems must be tackled: how can thetransitional characteristics of ground motion be measured quantitatively and how do ground characteristics affect human behavior.
We here propose a new measure by which to express the transitional characteristics of ground motion and present a new index
that assesses the time available for evacuation. The comprehensive discussion and analysis of human behavior during earthquakes
need to take into account many factors, such as the structural
response, indoor environment disruption, and the type of humanactivity at the time of an earthquake, as well as the characteristics
of ground motion. The available evacuation time addressed in thispaper therefore does not cover all the parameters related to human

KEY WORDS: Instantaneous Instrumental Seismic Intensity (IISI), human behavior, 2000 Western Tottori, Japan earthquake

36

Y. KUWATA & S. TAKADA

evacuation behavior, rather it introduces as a relevant element thetime available for evacuation based on the Instantaneous
Instrumental Seismic Intensity.
2.

SITE SURVEY OF THE 2000 WESTERN TOTTORI,JAPAN EARTHQUAKEThe 2000 Western Tottori, Japan earthquake that occurred inwestern Tottori Prefecture (35.3N, 133.4E, 10km) at 13:30 on
October 6, 2000 had the magnitude MJMA7.3, Mw6.6 (Figure 1).
The damage survey published by Tottori Prefecture (2002) showeda total of 393 collapsed houses, 2,491 houses moderately damaged,
and 141 people injured. High seismic intensity of 6+ on the Japan
Meteorological Agency (hereafter JMA) scale occurred at
Sakaiminato City and Hino Town in Tottori Prefecture. Hino
Town (129 collapsed and 441 moderately damaged houses) is
close to the epicenter, and Sakaiminato City (71 collapsed and 287
moderately damaged houses) is 30 km northwest of it. Most of thedamage occurred in the mountainous area.
A site survey of the collapsed houses in Sakaiminato City was
made immediately after the earthquake (Takada et al., 2000). The
16 collapsed houses reported on the third day after the earthquakeby the Sakaiminato City Municipal office were surveyed. Table 1
lists them.

With respect to overall features, they are wooden structures
built more than 50 years ago. Their roofs were heavily tiled towithstand typhoons. In all cases, nearby newly constructed houses
did not suffer damage to their main structural components. Aninteresting feature was that all the completely collapsed and tilted
houses leaned to the east. People living near the damaged houses
said that only furniture set on the north-south axis was dislocated.
The peak ground acceleration recorded at the Sakaiminato
Meteorological Observatory was 748 gal for the EW component,
higher than the 299 gal for the NS component. This particular pattern of direct damage is due to the predominant direction of groundmotion.
Evacuation behavior of those whose houses collapsed wasreported. In case 3, Table 1, neighbor reported that an elderly
woman was at home during the earthquake, but she did not suffer
severe injuries although she was taken to the hospital. Her house
was heavily tilted (Photo. 1). In case 6, an elderly woman was
having an after-lunch nap. She became aware of the shaking andrushed to the front door. After she had run about 5 meters fromher house, it completely collapsed with a loud noise (Photo. 2). In

N

0
W

10

20

E

Km
S

6+ Sakaiminato City
6-

5- 5-

6-

5+

Photo 1. Case 3

Photo 2. Case 6

Photo 3. Case 10

Photo 4. Case 14

56-

6-

6-

×Epicenter

Tottori Pref.

6-

66+

6-

Fig. 1

Location of Sakaiminato City

Table 1. List of collapsed houses surveyed in Sakaiminato City

INSTANTANEOUS INSTRUMENTAL SEISMIC INTENSITY

case 13, an elderly man with a crippled leg felt the earthquake andcrawled out of his house with help of his family. That house did
not collapse completely (Photo. 3). In case 14, a young woman
and her father who were on the first floor were frightened by theshaking ran out from the entrance. Just after they got out, thehouse collapsed (Photo 4), but they were not injured.
In this earthquake, those houses that completely collapsed did
not cause death to the persons inside. The main reason for this isthat something other than structural resistance (which was not sufficient to resist the earthquake) helped to reduce the number ofcasualties. Three factors: the hour of the day, indicative of low
occupancy; the wide and multiple outlets from the houses; and thetime available for evacuation, were involved.

37

after it the vertical component was added to the ISI. The new measure uses a calculation method which computes the ISI value as
instant duration, and therefore is named Instantaneous Instrumental
Seismic Intensity (hereafter IISI).
The IISI is calculated by three steps (Figure 2). The first is tocompute the Fourier spectrum of acceleration in each component(2 horizontal and 1 vertical) and to multiply the spectrum by threekinds of filter functions (as follows), then to compute the filteredacceleration by its inverse Fourier transform.
F1 (ω) = (1/ω)1/2(1)F2 (ω) = (1+0.694X + 0.241X + 0.0557X + 0.009664X 8+ 0.00134X 10 + 0.000155X 12)1/2
(2)
2

4

6

subject to X = ω/ωc
1. Low occupancy: Most people were not at home and those who
were resting on the first floor as the earthquake occurred at
13:30 in the early afternoon hours of a weekday. People were
awake and at once perceived the shaking and moved.
According to the statistics on hourly human behavior (NHK,1990), the inhabitant occupancy (the percent at home) at 13:30
was 27 % and almost all were awake. In contrast, early in themorning when the Hyogoken nambu earthquake occurred 96 %occupancy was estimated. The number of those at home during
the Tottori Western earthquake was much lower.
2. Wide and multiple outlets: There were more and wider
entrance doors and windows in the houses in Sakaiminato City
than in Kobe. Such multiple outlets can provide inhabitants
many easy escape routes.
3. Time available for evacuation: Before houses collapsed, there
was time enough for people to get out. The ability of elderly
people to escape in earthquakes has been shown to be lower, asconfirmed by a Taiwan earthquake case study (Kuwata and
Takada, 2001), but the elderly people reported here were able tomove and get out of their houses during the earthquake. In
addition, some people said that they were able to turn off thegas in the kitchen before evacuating. In the case of Kobe, survivors said buildings suffered damage as soon as they felt theshaking, whereas in Tottori, most of the people interviewed said
that their houses collapsed only after they had escaped.
The first two factors are functional ones related to the vulnerability component, and the last is related to the characteristic of
input ground motion. Ground motion has been often assessed interms of peak intensity and predominant frequency. Our casestudy indicates that there is a transitional characteristic during
ground shaking, which allows people to move to safer locations.
Consideration of the transitional characteristic of ground motion
provides a chance to analyze human behavior in dynamic ways,
but there is no available measure besides ground motion records
with which to evaluate that instantaneous value.

F3 (ω) = (1-exp (-(ω/ω0) 3))1/2

3. TRANSITIONAL CHARACTERISTIC OF SEISMIC
INTENSITY
3.1 Instantaneous Instrumental Seismic Intensity
A new measure is proposed related to the Instrumental
Seismic Intensity (hereafter ISI) adopted by the JMA in 1996
(JMA, 1996). Whereas before the Hyogoken nambu earthquake
only the two horizontal acceleration components were considered,(3)

where F1 (ω) is a filter corresponding to human sensitivity toshaking, F2 (ω) a high cut filter, F3 (ω) a low cut filter, ω the frequency, and ωc and ω0 are parameters of the high and low cut filters (ωc = 10Hz, ω0 = 0.5Hz).
The next step is to calculate the vector acceleration,ν(t), bysumming the three components of the filtered accelerations. In thethird step, the maximum amplitude, a0, of vector acceleration thatsatisfies more than 0.3 second duration as in the ISI calculation isdetermined. The duration is defined as the sum of the time intervals between first and final peaks that exceed a threshold level ofvector acceleration. In the calculation, the vector acceleration
series (ν(k),ν(k+1),...ν(k + j)) from the beginning, time k, isFig. 2IISI calculation method

38

Y. KUWATA & S. TAKADA

selected based on a given time window. A vector acceleration
series is sorted from the large to small amplitudes (s(1), s(2),... s (j+ 1)), and the maximum amplitude is obtained based on the above
condition. The IISI (k) at time k is computed by a formula which isrelated to the Kawasumi formula (Kawasumi, 1943).
IISI (k) = 2・log a0 (k) + K(4)

where K is a parameter, equal to 0.94.
The IISI at another time can be calculated by shifting the time
window of the vector acceleration series. Almost all the parameters and conditioning functions follow those in the ISI procedure.
The IISI calculation procedure takes into account two additional

Fig. 3parameters; the duration of the time window and the shift to thefollowing time window. If the calculated value is less than 0.0, the
IISI is regarded as equal to 0.0. The point at which the value of
IISI exceeds 0.0 is defined as the beginning of the IISI.
3.2

Application to the Western Tottori and the Hyogoken
nambu earthquakes
In this application of the new index, 0.5 second time windows,
with 0.1 second shifts between, are used. Figure 3 shows the IISIs
of several accelerograms during both earthquakes (JMA Kobe
(JMA), Kobe University, Toyonaka (CEORKA, 1995), Kohhu,
Yonago (NIED), and Sakaiminato (JMA)), for which the time axes

Instantaneous Instrumental Seismic Intensity and Smoothing CurveINSTANTANEOUS INSTRUMENTAL SEISMIC INTENSITY

are set at the beginning of IISI. The peak IISI arrival time, definedas the time from the beginning of IISI to its maximum, was short(about 5 seconds) at JMA Kobe in the Hyogoken nambu earthquake. In contrast, values in the Western Tottori earthquake are
relatively long, especially at Sakaiminato (about 10 seconds).
Figures below the IISI charts show the smoothing curves ofabsolute accelerations. The IISI peak point well corresponds to thehorizontal acceleration peak. These peak characteristics are drawn
by the envelope curves of ground motion as well as by the IISI.
With respect to transitional characteristics up to the maximum IISI,
for the Western Tottori earthquake the shapes of the smoothing
curves until the peak points are similar for the three acceleration
components, whereas for the Hyogoken Nambu earthquake, firstvertical acceleration increases. Although the maximum IISI
depends on the horizontal acceleration, the transitional duration
characteristics from the beginning to the peak arrival mainly are
determined by vertical acceleration.
Acceleration records at the JMA Kobe and Kohhu observatories show almost the same peak ground accelerations, 818 and 748
gal, whereas the calculated maximum IISIs differ 6.3 and 5.6. The
maximum IISI slightly differs from that of the ISI due to the condition of the time window. The maximum IISI is almost equal to, orat most 0.3 less than, the ISI. The difference between the PGA andmaximum IISI is due to the predominant frequency of acceleration.
IISI calculation uses the filtering procedure to meet building damage and human perception. The IISI is reported to better fit building damage caused by earthquakes than the PGA (Kuwata et al.,2001). In fact, building damage at Kohhu was less than in Kobe.
Two factors explain why inhabitants had the time to evacuate
in Sakaiminato City: the peak arrival time was long, and the IISI
was not high enough to correspond to PGA as it did in Kobe.
The advantage of utilizing the IISI is that the peak arrival time
and transitional characteristics of three components can be treatedas simple integrated value that agrees well with building damage
and human perception. The weak point is that it involves complicated calculations. The IISI, however, can be used to assess past
research on human behavior during earthquakes because thesestudies were done using the seismic intensity given on the JMA
scale.

on the people who are entrapped and cannot escape.
When a given ground motion intensity increases, the period
proceeds from ① to ④, and physical factors increasingly become
more important than human behavior. In period ④, the situation iscompletely determined by the physical damage done. Period progression depends on the transitional intensity of ground motion.
The most important factor affecting human loss is the time atwhich a building starts to collapse. This needs to be determined byadopting structural perspectives. An analysis of structural
response and durability combined with the IISI has been published(Kuwata and Takada, 2002), but more investigation is required.
Our paper deals mainly with the time available for evacuation.
The following discussion therefore specifies the time available for
evacuation in period ②.
Human perception depends not only on felt ground motion,but on buildings responses to that motion. We propose a basicmodel that uses only observed acceleration records. Groundmotion characteristics that are important in assessing a building s
response will be considered in the future as added parameters.
A review of several studies on human behaviors during earthquakes shows there is a relationship between peak seismic intensity and human behavior. Okada and Kagami (1991) showed that
50% those surveyed felt they could not move at all at a level of
5.08 seismic intensity. Kosaka (1993) showed that the thresholdfor people s action, e.g., turning off fires, is a seismic intensity of
4.0. These intensities were derived from questionnaires distributed
to people affected by earthquakes.
The explanation of the scale of seismic intensity used by the
JMA (1996), completed after the 1996 revision of the JMA seismic
intensity scale, shows the typical phenomena and damage experienced at each point on the seismic intensity scale. In that list, thesituation, in which most people are very frightened and find it difficult to move around, corresponds to the ISI of 5.0, and most people in buildings can perceive an earthquake at the ISI of 1.5.

4. TIME AVAILABLE FOR EVACUATION
4.1 The human behavior period
If the IISI can be used as a new intensity measure, the problem is how can transitional characteristics used as a parameter ofground motion be used to evaluate the time available for evacuation. Our strategy in dealing with this problem was to divide theduration of ground motion into four characterized periods then to
indicate the time available for evacuation when combined with aground motion measure.
These four periods, based on human behavior and surrounding
conditions for a certain intensity of ground motion are
period ① : people do not feel any ground motion,
period ② : people are aware of the earthquake and are able toevacuate,
period ③ : people cannot move, surrounding objects fall, butbuildings do not completely collapse, andperiod ④ : buildings completely collapse, surrounding objects fall39

Fig.4 Arrival time of each IISI level

Table 2. Time available for evacuation

40

Y. KUWATA & S. TAKADA

4.2 Application
No study of the relationship between IISI and human behavior
has been done published. Our research involves the above seismic
intensities found based on answers given in a questionnaire and the
ISI. We are convinced that even though questionnaire-derived
intensities are not all that reliable from a scientific standpoint, they
well fit findings for human behavior during earthquakes (Takada
and Ueda, 1998).
Based on the above reviews, the threshold between periods ①
and ② is defined as the 1.5 IISI level, and that between periods ②
and ③ the 4.0 to 5.0 IISI level. It is difficult to give a definite
threshold between periods ② and ③ because they partially overlap
and are influenced by many factors. The time available for evacuation therefore ranges from 1.5 to 4.0, or 5.0 (Figure 4), as calculated from the acceleration records in Figure 3. Results are shownin Table 2. Sakaiminato City had the longest available evacuation
time. Results show that the time available in the Western Tottori
earthquake was relatively longer than that in the Hyogoken nambu
earthquake. The time available close to the epicenter was shorter,
for example at JMA Kobe and Kohhu. The available time, however, does not always depend solely on ground motion characteristics, but on the location and distance from the epicenter as well.
5.

FURTHER EXAMINATION AND FUTURE APPLICATIONS
The outlines of the new measure and model for evaluating thetime available for evacuation have been given. In terms of theirpractical use, further analysis is needed to deal with various
aspects. Above of all, prediction of the IISI can be used to estimate the time available for evacuation in order to reduce earthquake-related casualties. The advantage is that it takes into
account the hazard uncertainty before an earthquake occurs, as in
the hazard maps based on PGA and seismic intensity.
The entire shape of IISI history has been investigated successfully by means of some parameters focused on sites close to active
faults for shallow earthquakes (e.g., Ozaki and Takada, 2001,
2002). That research succeeded in predicting a time history ofground motion based on the IISI.
The purpose of the following examinations is to determine thethresholds between periods in order to apply the proposed model toa given earthquake. For earthquakes with focal depths shallower
than 20 km (NIED), the IISI arrival time is analyzed taking into
account the hypocentral distance and two levels of earthquake
magnitude. Acceleration records of 16 earthquakes, magnitudes ofwhich were either 7.2 or 7.3 on the JMA scale, and of 17 earthquakes whose magnitudes ranged from 6.1 to 6.3 on the same scale
were used. Figures 5 and 6 respective show IISI arrival times oflevels 4.0 and 5.0. Only 6 of the 18 acceleration records, which
had magnitudes 6.1 to 6.3, had arrivals of level 4.0. Both figures
show that each arrival time is proportional to the hypocentral distance. Magnitude differences are not closely related to IISI arrival
time 4.0. Here the arrival time is discussed mainly for near field
earthquakes, but a generic chart will be made from results of future

Fig.5 IISI arrival time related to hypocentral distance for IISI 4.0

Fig.7

Maximum IISI related to magnitude and hypocentral distance for an IISI of 4.0

Fig.6 IISI arrival time related to hypocentral distance for IISI 5.0

Fig.8

Maximum IISI related to magnitude and hypocentral distance for an IISI of 5.0

INSTANTANEOUS INSTRUMENTAL SEISMIC INTENSITY

examinations of earthquakes of various magnitudes and focal
depths and those of large magnitudes in oceanic plates.
Figures 7 and 8 show the arrival times of 112 earthquakes
with focal depths shallower than 20 km in relation to magnitudeand hypocentral distance. In Figure 7, a closed circle indicates thatthe maximum IISI reaches level 5.0, an open circle that it does not.
Figure 8 likewise shows the case for an IISI of 4.0. The maximum
IISI appears to be affected by the site ground and other local conditions, therefore, the threshold is not clear. The hypocentral distance reached at IISI 5.0 could be identified for a given earthquake
magnitude based on Figure 8. This chart can be used to obtain thecorresponding arrival time on the IISI scale by combining the magnitude level and hypocentral distance. For example, given an
earthquake of magnitude 6, the target IISI arrival time of 4.0 isobtained, which corresponds to a hypocentral distance of less than
30 km.
Results of this research on the IISI provide researchers with
beneficial information and a different view of ground motion parameters one that specifically addresses human casualties caused byearthquakes. The simpler and more easily understandable chartsthat show threshold lines in Figures 5 and 6, and hazard maps thatshow the time available for evacuation can help residents become
more aware of earthquake threats. For a comprehensive humanbehavior model, however, several parameters besides the IISI must
be considered.
CONCLUDING REMARKS
By reviewing the case of Sakaiminato City during the Western
Tottori earthquake, the need for the transitional characteristic ofground motions was brought out in studies of earthquake-related
casualties. A new measure of ground motion combined with amodel indicating the time available for evacuation is proposed, andapplications of the proposed model are shown. The following conclusions were obtained:
1. As a measure of the transitional characteristic of groundmotion, Instantaneous Instrumental Seismic Intensity is proposed. It explains not only the peak intensity and time to reachthat intensity but the transitional characteristics up to the peakintensity. This measure is more useful than the envelope curveof ground motion because as a simple measure it can treat complex characteristics that involve the vertical components.
2. To indicate the time available for evacuation, a transitionalmodel characterizing human behavior and surrounding conditions is introduced. The duration of ground motion is divided
into four characterized periods, and the time available for evacuation presented with the associated period sets.
3. The proposed measure and model were applied to the Western
Tottori and Hyogoken nambu earthquakes. The time available
for evacuation in Sakaiminato City was shown to be longer thanthat in Kobe. This longer period is supposed to have been an
important factor for facilitating peoples s escapes.
4. Practical applications of the proposed measure and model are
shown. The relationship between the IISI arrival time andhypocentral distance for two levels of earthquake magnitude
show that the time available for evacuation depends on the
hypocentral distance. Although analyses of other earthquakes
are needed, clearly the threshold for evacuation activity is limited by the closeness to the earthquakeÅfs source, when the event

41

is of large magnitude.
5. For a comprehensive model of human evacuation, more investigation is needed related to factors such as building resistance,
disruption of surrounding indoor objects, and human perception
meeting with the IISI.
ACKNOWLEDGMENT
First author thanks the Japanese Society for the Promotion of
Science (Grant-in-Aid for Scientific Research, DC1, No. 09368)
for its support of this research.
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