Microzonation considering large earthquake


Saragoni, G.R.; Carvajal, A.

International Conference on Seismic Zonation 4: 495-502

1991


MICROZONATION
CONSIDERING
LARGE
EARTHQUAKE.
G.R.Saragonir
and
A.
Carvajal"
ABSTRACT
Large
magnitude
eaethquakes
8.0)affect
Valparaiso,
Chile
among
them,
the
Richter
magnitude
8.3
of
1906
was
the
most
des-
tructive
of
this
century.
The
damage
was
concentrated
in
the
small
zone
of
"El
Almendral"
of
Valparaiso.
This
historical
damage
information
was
studied
and
classified
allowing
to
produce
a
microzonation
map
based
on
real
observed
damage
of
alarge
earth-
quake.
Furthermore
knowing
that
these
large
earthquakes
happen
every
85
years
due
to
particular
seismological
conditions
an
accelerogra-
phic
experiment
was
set
up
to
measure
the
next
large
earthquake
in
fill
and
rock
at
epicentral
conditions.
The
station
in
fill
was
located
close
to
the
zone
of
the
largest
observed
damage
of
the
1906
earthquake.
Accelerograms
were
obtain-
ed
at
both
stations
for
the
1985
chilean
earthquake
(Ms
=7.8).
The
Fourier
spectrum
of
these
records
were
analyzed
and
compared
with
theoretical
multilayer
solutions.
It
is
concluded
that
soil
amplification
obtained
can
be
explained
as
a
combination
of
soil
amplification
and
source
mechanism
effect.
The
obtained
microzoning
from
the
damages
of
1906
earthquake
is
in
agreement
with
the
resulting
from
the
damages
of
1985
with
an
in-
crease
of
Mercalli
intensity
of
1
1/4.
Microzonation
map
based
on
large
earthquake
remain
unchanged.
The
extreme
Mercalli
intensity
values
for
each
zone
must
be
estima-
ted.
I
Professor,
Structural
Engineering
Division,Dept.
of
Civil
Engineering,
University
of
Chile/Cas'illa
228-3/
Santiago,
Chile.
II
Civil
Engineer,
Structural
Engineering
Division,
Dept.
of
Civil
Engin-
eering,
University
of
Chile/Casilla
228-3/Santiago,
Chile.
*
Presenting
Author
Underlined
495
INTRODUCTION
The
central
zone
of
Chile
is
characterized
to
be
affected
with
extreme
regularity,
every
85
years,
by
large
off-shore
earthquakes
of
Richter
magnitude
larger
than
8.0.
These
earthquakes
with
epicenter
in
front
Valparaiso
stroke
Valparaiso,
Vina
del
Mar
and
Santiago.
Therefore
these
earthquakes
represent
the
extre-
me
design
condition
for
the
central
part
of
Chile.
Among
the
large
historical
earthquakes
of
Valparaiso,
the
one
of
August
16,
1906
of
Richter
magnitude
8.3
is
the
most
destructive,
with
3882
victims
and
completly
destroying
the
El
Almendral
zone
of
Valparaiso.
Due
to
this
reason
the
characteristics
and
damaging
effects
of
this
earthquake
are
studied
in
detail
in
this
paper.
The
historical
description
of
the
damage
it
was
found
to
be
of
good
quality
to
perform
a
microzoning
map
of
high
standard.
LARGE
HISTORICAL
VALPARAISO
EARTHQUAKES
The
main
characteristics
of
the
large
Valparaiso
earthquakes
are
summarized
in
Table
1.
In
this
table
are
indicated
the
estimated
values
for
the
rupture
length
L,
the
width
W,
the
average
displacement
AW,
the
Richter
magnitude
and
the
seismic
moment
Mo.
The
periodicity
of
85
years
of
the
Valparaiso
large
earthquakes
is
consecuence
of
the
stress
accumulation
at
a
constant
rate
in
an
aspirity
for
a
subduction
velocity
of
convergence
of
10
cm/year
141.
TABLE
1.
Characteristics
of
Valparaiso
Earthquakes
Date
Rupture
Length
L
1Km1
Width
W
'Km!
Average
Dis-
placement
AD
Imi
Magnitude
Seismic
Mo-
ment
Mo
10
27
dinas-cm
1575
(7-7.5)a
1647
365b
8.5a
1730
350-450c;550
01
100-150e
6-8e
8.75a
1E22
200-250b;330e
100-150
e
3-6e
8.5a
1906
365b;330e
100-150e
3_6e
8.2f;
8.3c
29-50e
1985
170b
100b
1.23b;
1.60c
7.8f
10-11.5c
a.-
Ref.
1
b.-
Ref.
3
c.-
Ref.
4
d.-
Ref.
5
e.-
Ref.
6
f.-
Ref.
2
SOIL
CHARACTERISTICS
OF
VALPARAISO
The
urban
zone
of
Valparaiso
is
located
on
an
ancient
shore
cover
with
artificial
fill.
The
"El
Almendral"
district
has
3
different
zones
of
soils.
The
Zone
I
between
the
shore
and
Brasil
Ave.
with
claimed
soil
of
5.5
to
8.5
m
depth.
The
Zone
II
between
Brasil
Ave.
and
the
hills,
with
ar-
496
tificial
fill
of
4
to
5
m
and
the
Zone
III
along
the
cliff
(Acevedo
et
al.(10)).
CHARACTERISTICS
OF
THE
DAMAGE
OF
1906
EARTHQUAKE
For
the
survey
of
the
damage
of
the
1906
earthquake
all
the
available
information
was
reviewed.
Most
of
the
information
for
this
study
was
obtai-
ned
from
the
publication
of
Rodriguez
and
Gajardo
171.
The
damage
description
for
El
Almendral
district
done
by
Rodriguez
and
Gajardo
is
given
block
by
block
with
36
photographies.
For
each
photo-
graphy
the
MSK
intensity
was
estimated
using
the
method
given
by
Monge
181.
With
the
estimated
intensities
for
each
block
of
El
Almendral
district
the
microzoning
map
of
Figure
1
was
done.
In
this
map
an
small
zone
has
the
maximum
intensity
of
X.
Perreta
and
Canales
191
performed
the
microzonation
of
Valparaiso
con-
sidering
the
damage
information
of
the
1985
chilean
earthquake.
This
micro-
zoning
map
is
shown
in
Figure
2.
The
microzonation
of
the
damages
lead
to
the
same
zones
of
the
micro-
ning
obtained
from
the
damages
of
the
1906
earthquake.
Both
microzonation
concide
with
the
soil
structure
of
El
Almendral.
The
Modified
Mercalli
intensity
relation
between
both
earthquakes
for
each
zone
of
El
Almendral
is
indicated
in
Table
2.
TABLE
2.
Comparisson
of
MMI
for
1906
and
1985
Earthquakes
at
El
Almendral
District.
Zone
Earthquakes
1906
1985
Increment
of
intensity
Zone
1
9
1/4
8
1
1/4
Zone
2
9
7
3/4
1
1/4
Zone
3
8
7
1/2
1/2
Zone
4
10
8
1/2
1
1/2
a.
Zones
according
to
Ref.
5.
The
increment
of
intensity
from
Table
2
is
about
1
1/4
for
an
incre-
ment
of
half
degree
in
the
Richter
magnitude.
It
is
observed
a
saturation
of
the
influence
of
the
Richter
magnitude
in
the
damage.
The
1906
earthquake
which
represents
the
extreme
epicentral
conditions
in
the
central
part
of
Chile
had
a
maximum
intensity
of
9
1/4,
with
the
exception
of
a
very
small
zone
of
intensity
10.
A
very
important
characteristic
of
this
large
earthquake
is
the
almost
no
damaging
condition
in
hard
soil
and
rock
in
the
hills.
This
is
a
challanging
feature
to
understand
the
reduced
destructiveness
potential
of
497
OCEANO
PACIFICO
94
r
--
0
r
-
n
I
.
sc.
C
°
C
'
VZ
C
°
V/R6LAI
olt
z
-C
Lit
IPI
A6U4
c-4
/-1LEC.
FIG.
1,
MODIFIED
MERCALLI
INTENSITY
FOR
MASONRY
BUILDINGS.
El
ALMENDRAL
DISTRICT.
1906
VALPARAISO
EARTHQUAKE.
v
rt
I C
i
c'
N
ry
7
1
/
2
lfa
ci
`,c`
Fik
S
\••
rn3.;
;
k
3,
r
FIG.
2
MODIFIED
MERCALLI
INTENSITY.
VALPARAISO.
EARTHQUAKE
MARCH
3,
1985
498
chilean
earthquakes.
SOIL
AMPLIFICATION
EFFECTS
IN
ACCELEROGRAMS
OF
1985
CHILEAN
EARTHQUAKE
Knowing
the
large
Valparaiso
earthquake
happen
every
85
years
an
acce-
lerographic
experiment
was
set
up
to
measure
the
next
large
earthquake
in
El
Almendral
district,
close
to
the
zone
of
intensity
10
of
the
1906
earthquake.
Two
acceIerograms
were
obtained
for
the
1985
chilean
earthquake
(Ms
=
7.8)
one
in
fill
in
El
Almendral
at
the
"12
ApOstoles"
church
and
one
in
rock
at
2
Km
from
the
previous
station
at
Santa
Maria
University
station.
The
main
characteristics
of
these
accelerograms
are
indicated
in
Table
3.
TABLE
3.
Characteristics
of
Valparaiso
Accelerograms.
1985
Chile
Earthquake.
Station
Component
4max
vmex
dmax
PD
vo
to
Igl
lam/s1
10'
4
g*sec
3
cross
/sec
Iseci
El
Almendral
N50°E
0.290
28.59
5.37
47.33
8.40
87.845
540°E
0.163
16.89
2.81
46.71
7.12
87.835
Vertical
520
2
E
0.164
6.40
1.33
3.44
11.61
79.425
N70°E
0.179
14.70
3.26
5.87
11.14
79.415
Vertical
0.125
5.85
1.37
1.23
14.36
79.405
U.T.F.S.M.
The
soil
characteristics
obtained
from
a
56
m
drill
done
by
IDIEM
of
University
of
Chile
up
to
rock
at
"12
ApOstoles"
church
site
are
indicated
in
Table
4.
TABLE
4.
Soil
Properties
"El
Almendral"
Station
(12
ApOstoles
Church).
Go
Eo
Imi
1Kg/cm
2
1
IKg/cm
2
1
IKg/cm
3
1
0-4
0.10
3055
6700
2700
4-20
0.12
4900
10900
2700
20-32
0.26
2250
5670
2700
32-56
0.38
1790
4960
2700
In
this
table
h
is
the
depth
in
m,
p
the
Posisson
modulus,
Go
the
shear
modulus,
E
0
the
Young
modulus
and
the
specific
weight.
The
shear
wave
velocity
were
estimated
in
350
m/sec
for
the
first
8
m,
275
m/sec
for
the
next
8
m,
300
m/sec
for
the
next
16
m
and
255
m/sec
for
the
last
24
m
in
contact
with
the
rock.
499
With
these
values
a
fundamental
period
for
the
soil
of
0.844
sec.
(W
I
=
1.1787)
was
estimated.
The
Fourier
amplitude
spectrum
ratio
between
El
Almendral
(fill)
and
Santa
Maria
University
(rock)
was
obtained.
The
result
is
shown
in
Figure
3.
In
this
figure
the
three
main
frequencies
are
identified
by
the
peaks
values.
In
Table
5
are
summarized
the
three
main
frequencies
wi
of
the
soil
with
their
corresponding
amplification
factors
RI,
R2
,
R3
obtained
from
the
Fourier
spectrum
analysis.
These
values
are
compared
with
the
theoreti-
cal
ones.
The
theoretical
values
of
the
frequencies
coincide
with
the
experimen-
tal
ones,
specially
for
w1
and
w
2
.
However
the
experimental
values
of
the
amplification
factors
Ri
are
up
to
3
times
different
from
experimental
ones.
This
difference
can
not
be
only
explained
by
the
soil
amplification
effect,
and
earthquake
mechanism
effect
should
be
considered
for
large
earthquake
in
epicentral
zone.
TABLE
5.
Soil
Amplification
Factors
and
Natural
Frequencies
for
"El
Almendral"
Station.
Fill
Rock
w
i
R1
W2
R
2
W
3
R
3
T
i
540°E
N70°E
1.2088
3.984
3.6264
2.640
6.044
1.176
0.8273
540°E
520°E
1.2210
10.165
3.5221
2.057
7.985
1.770
0.8190
N50°E
N70
2
E
0.9768
4.108
3.2360
2.460
7.057
2.468
1.0238
N50°E
520°E
0.7692
7.165
4.5675
2.573
7.741
3.352
1.3000
Theoretical
Value
1.1787
2.7951
3.5361
2.7951
5.8928
2.7951
0.8484
In
order
to
separate
the
relative
influence
of
the
dynamic
soil
ampli-
fication
and
the
source
mechanism
effect
in
the
observed
amplification,
the
ratio
between
Fourier
spectrum
was
again
considered
for
Villa
del
Mar
520°W
and
Santa
Maria
University
520°E
accelerograms;
for
the
main
shock
and
the
one
hour
after
"main
aftershock".
The
results
are
shown
in
Figure
4.
Comparison
of
both
amplification
curves
shows
that
their
values
depend
of
the
size
of
the
earthquake,
keeping
for
both
quakes
the
main
frequency
of
amplification.
This
result
shows
the
importance
of
the
source
mechanism
in
the
amplification
factor.
Therefore
soil
amplification
effect
may
not
be
adequate
estimated
using
small
quakes.
ACKNOWLEDGEMENTS
The
results
reported
herein
were
obtained
as
part
of
the
research
project
FONDECYT
0137/86.
500
R
ATI
O
O
F
FOU
RI
ER
AM
PL
I
TU
DE
12
0
11.0
10.0
1.0
8.0
7.0
0.0
5.0
4.0
3.0
2.0
0E.10.
DE
I06E010010
CIVIL
U.
DE
COILS
5110010.80
II11E5
10
.
.0
0.0
o
0
t
r
5.0
15.0
20.0
Veke
i‘Ai
25
'
.0
3010
WI
35.0
(J.
FRECuEmCIA
ICPSI
FIG
3
RATIO
SOIL
/ROCK
AL
-S/i0E
/
US
-S
20
E
14
3
13.0.
12.0
.
11.0
.
10.0
.
MAIN
SHOCK
RA
TIO
O
F
FOU
RIE
R
AM
PL
ITUDE
9.0
.
8.0
.
7.0
.
6.0
.
5.0.
4.0.
3.0
.
"1
HOUR
AFTER
AFTERSHOCK"
2.0
.
1.0
.
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
NATURAL
PERIOD
Tn
(sec.)
FIG
4
RATIO
OF
FOURIER
AMPLITUDE
BETWEEN
VIVA
DEL
MAR
S
20f'
W
AND
U
T
F
S
M
S20°E
MAIN
SHOCK
AND
1
HOUR
AFTER
AFTERSHOCK
MARCH
3,
1985
501
REFERENCES
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Lomnitz,
C.,
"Major
Earthquake
and
Tsunamis
in
Chile
during
the
Period
1535
to
1953".
Geolog.
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pp.938-960,
1970.
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Pereira,
M.L.,
J.
Crempien
y
G.R.
Saragoni,
"Study
and
Installation
of
a
Local
Accelerographic
Network
of
High
Density
in
a
Fractured
Sub-
duction
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Pardo,
M.,
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Singh,S.K.
And
SArez,
G.,
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1985
Central
Chile
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:
A
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in
the
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?",
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233,
393-500,
1986.
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Kausel,
E.,
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Process,
Focal
Parameters
and
Aftershocks
of
the
March
3,
1985
Earthquake",
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the
book
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Chile
Earthqua-
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3,
1985",
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Monge
(Editor).
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spanish).
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Carvajal,
A.
and
G.R.
Saragoni,
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the
Valparaiso
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of
1906
and
March
3,
1985",
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Division
Report,
Civil
Engineering
Dept.,
University
of
Chile,
1989.
6.
Nishenko,
S.P.,
"Seismic
Potential
for
Large
end
Great
Interplate
Earthquake
along
the
Chilean
and
Southern
Peruvian
Margins
of
South
America
:
A
Quantitative
Reapraissal", Journ.
of
Geophysical
Research,
Vol.
90,
pp.
3589-3615,
April
10,
1985.
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Rodriguez,
A.
y
Gajardo,
C.,
"La
Catastrofe
del
16
de
Agosto
de
1906
en
la
RepOblica
de
Chile",
Imprenta
Barcelona,
Santiago,
Chile,
1906.
8.
Monge,
J.,
"Earthquake
Engineering
Design"
(In
spanish),
Pub.
SES
D
1/80
(158),
1981,
Dept.
of
Civil
Engineering,
University
of
Chile.
9.
Perretta,
C.
and
J.C.
Canales,
"Study
of
March
3,
1985
Earthquake
in
Valparaiso
District",
Civil
Engineering
Thesis,
Dept.
of
Civil
Engin-
eering,
University
of
Chile,
1988
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