Transcript Site Effects

ADVANCES AND PROBLEMS
IN UNDERSTANDING THE
SEISMIC RESPONSE OF
POTENTIALLY UNSTABLE
SLOPES
Vincenzo Del Gaudio1 and Janusz Wasowski2
1. Dipartimento di Geologia e Geofisica, Universita` di Bari, Bari, Italy.
2. Istituto di Ricerca per la Protezione Idrogeologica, Consiglio
Nazionale delle Ricerche, Bari, Italy.
報告者：林子翔
指導教授：李錫堤
報告日期：01/06
SEISMIC RESPONSE
Site effect
Picture from：
大地地理雜誌
Source
effect
Path effect
National Central University
Graduate Institute of Applied Geology
SITE EFFECTS
 May
20 &17,
November
September
October
19,
1989
1985 15,1986
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Graduate Institute of Applied Geology
Research
motive
1. Why are we studying the site effects on
unstable slopes?
2. What conditions will the site effects happen?
3. What will happen cause by site effects?
4. Our comprehension from previously studies in
this problem
5. The expect of improvement and breakthrough
through this study
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Research
motive
ACCELEROMETRIC MONITORING OF
CARAMANICO LANDSLIDE-PRONE SLOPES.
The influence of site ef fects on landslide triggering during
earthquakes has been inferred in several studies, but its
evaluation is made dif ficult by the complexity of factors
controlling the dynamic response of potentially unstable slopes
and also by the lack of local ground motion instrumental
observations.
Considering the above, a local permanent network of
accelerometric stations was sited in2002 on unstable slopes in
a mountainous area of central Italy, around the town of
Caramanico.
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Study Area
ORFENTO AND ORTA RIVER VALLEYS
 high relief
 active river erosion
 strong permeability contrasts
between dif ferent lithologies
 abundant rainfall
 close to active seismogenic
structures
 a case triggered by an event that
was quite far away (with
epicentral distance more than
100 km)
ROMA
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Study Area
Maiella Mts.
Caramanico Terme
Mt. Morrone
Alto hill
N
Lm
1
2
3
4
Orfento River
CARAMANICO
Caramanico Terme
5
ta
Or
ver
Ri
Or
fen
to R
ive
r
Bq
ta
Or
b
sh
ver
Ri
Mp
Mp
Lm
0
100 m
Legend
Lm = limestones - Miocene;
Mp = marly mudstones, Early Pliocene;
Bq= carbonate megabreccias – Quaternary (?);
Sh = soils (colluvial materials, landslide deposits,
water-laid and eluvial sediments, artificial ground
– Holocene);
b = carbonate brecciaz (Quaternary);
1 = overthrust front of the Morrone Mt;
2 = faults;
3 = steep scarp of the megabreccia caprock;
4 = lithological limit;
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5 = spring.
Graduate Institute of Applied Geology
Study Area
Accelerometric monitoring of a landslide-prone slopes
at Caramanico Terme (Central Italy)
CAR3
CAR1
CAR2
2004.12.0
3
CAR4
CAR5
1 km
2002.10.10
2005.11.1
1
2006.03.27
2002.11.06
Study Area
accelerometric network
CAR2
CAR4
CAR1
= accelerometric stations.
= microseismic noise
measurements.
CAR5
地質年代(百萬年)
第四紀(1.8-today)
岩性代號
Bq
Quaternary limestone megabreccias
第四紀全新世(0.01-today)
Sqh
Quaternary and Holocene soils (colluvium and artificial
ground)
土壤(崩積層與人工地面)
第三紀上新世(5.3-1.8)
Mp
Pliocene mudstones
Me
Messinian sandy-silty deposits with carbonate breccia
泥岩
粉砂沉積物混和碳酸鹽質角礫
岩
石灰岩
石灰岩
第三紀中新世晚期(7.246–5.332)
第三紀中新世(23-5.3)
未確認年代
CAR3
Lm
L(m)
英文
Miocene
limestones of uncertain Miocene age
岩性
石灰質火山角礫岩
Study Area
Geologic profiles
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Data
Acquisition
WEAK GROUND MOTION DATA
Period
2002-2008
N. ev.
82
N. record
152
M>4 & N. rec >1
2
NO.
Launched
Car1
2002
Car2
2002
Car3
2004
Car4
2005
Car5
2006
Max Mag Max Dist.
5.7
161 km
Molise 2002 mainshock
Data
Acquisition
L’AQUILA EARTHQUAKE OF 6 APRIL 2009 (M W = 6.3)
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Data
Acquisition
L’Aquila earthquake of 6 April 2009 (MW = 6.3)
Period
2002-2008
2009-2010
N. ev.
82
119
N. record
152
332
M>4 & N. rec >1
2
14
Max Mag Max Dist.
5.7
161 km
6.3
149 km
Molise 2002 mainshock
L’Aquila 2009 mainshock
Up
Up
North
North
East
East
CAR1 recordings
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Graduate Institute of Applied Geology
WEAK MOTION DATA
2002-2008
Data
Analysis
CAR1 VS CAR2
CAR2
CAR1
2002.11.12
CAR2 (landslide site)
09:27:49 East
Acceleration (gal)
6
4
2
0
-2
-4
-6
0
10
20
30
40
50
Time (s)
CAR1 (substratum outcrop)
Amplification (16 events)
Average
Min
Max
PHA(gal)
1.36
0.83
1.83
Ia(m/s)
1.88
1.06
3.62
Data
Analysis
CAR3 VS CAR4
CAR3
CAR4
2006.06.05
00:07:50
East
Acceleration (gal)
15
CAR4 (reference)
10
5
0
-5
-10
-15
0
10
20
30
40
50
Time (s)
CAR3 (on breccias)
Amplification (18 events)
Average
Min
Max
PHA(gal)
1.02
0.30
4.75
Ia(m/s)
0.65
0.20
1.68
Research
Method
Calculate the Ia
Arias ( A r i a s ,
1 97 0 ) ,所定義AI之公式如下：
𝜋
𝐼𝑎 =
2𝑔
𝑇𝑑
𝑎 𝑡
2
𝑑𝑡
0
其中g為重力加速度（m/sec 2 ）；T d 為時間（recording duration）
（sec）；a(t)為測站接收到地震所產生的加速度值（m/sec 2 ），AI
單位為（m/s）。
(corrected for the instrument response with 20 Hz cut-of f frequency)
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Research
Method
Polar diagrams
and Calculate the ellipticity ratio
ellipticity ratio：
the ratio between maximum and minimum of Ia values
measured along horizontal directions at different Ia max

azimuths.
Ia
min
Using E-W and N-S components of the recordings to
calculate the Arias Intensity on accelerograms rotated at
10° azimuth intervals.
Polar diagrams show the directional variations of AI,
normalized by its maximum value.
Diagrams are given for a representative sample of
events differing for magnitude, distance and back-azimuth,
together with the average normalized AI values (NAIav),
calculated in different directions for all the recorded
events.
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Discussion and
Conclusions
PRELIMINARILY STUDY
Site Effects：
Support：
amplification
：
Hypothesis
： measurements of S-wave velocity with the technique of
Preliminary
1.
The dynamic
response
of Car2
compare
with Car1,an
average
refraction
microtremor
analysis [Louie,
2001]
gave values
of 300–600
m/s for
relative
byCAR2
a factor
ofattributed
2.2
in total
shaking
relativeamplification
amplification
at
was
to impedance
contrasta
theThe
landslide
material
and 1000–1500
m/s
for the
mudstone.
At energy.
CAR3
between
the site
colluvial
(landslide)
deposits
and
the both
underlying
mudstone.
contribution
to amplification
likely
derives
from
topographic
effect
and
2.
At the
CAR2
constantly
high
ellipticity
values
were
found,
impedance
carbonate
breccias
and underlying
with allcontrast
the Iabetween
maximatheoriented
within
a narrow
azimuth
limestones.
interval around the local maximum slope direction.
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Data
Analysis
POLAR DIAGRAMS OF NORMALIZED ARIAS INTENSIT Y
Max,0.90；min,0.83
Max,0.99,260°
Min,0.55,170°
Max,0.96,290°
min,0.33,200°
Max,0.89；min,0.59
Research
Method
SITE EFFECT EVALUATIONS
site ef fect evaluations by reference site method and nonreference sitemethod
HSS=Horizontal Spectrum of Sedimentary site
Reference
site method
HSR=Horizontal Spectrumof Reference site
HNS=Horizontal Noise of Sedimentary site
HNR=Horizontal Noise of Reference site
Borcherdt(1970)
HNS=Horizontal Noise of Sedimentary site
Non-reference
sitemethod
VNS=Vertical Noise of Sedimentary site
HSS=Horizontal Spectrum of Sedimentary site
VSS=Vertical Spectrum of Sedimentary site
Nakamura(1989)
Lermo and Chávez-García (1993)
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Data
Analysis
POLAR DIAGRAMS OF HVSR
CAR1
Horizontal - to Vertical Spectral
Ratio (HVSR)
from seismic
“weak motion”
data until 2008
(15 events)
CAR3
(19 events)
CAR2
(14 events)
CAR4
(7 events)
Discussion and
Conclusions
DIRECTIVIT Y
Site Effects：
Directivity ：
Given the occurrence of directivity in landslides, fault zones and
fault-bounded slopes, both with or without the presence of
ground motion amplification
This phenomenon can be masked by directivity related to source
ef fects, and hence its recognition requires the analysis of
several recordings of events with sources located at dif ferent
station-epicentre back-azimuths and having dif ferent focal
mechanisms.
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Graduate Institute of Applied Geology
STRONG MOTION DATA
2009L’AQUILA EARTHQUAKE
Data
Analysis
PRELIMINARILY STUDY
b)
2009.04.06
01:32:26 East
100
Acceleration (gal)
4.0
Amplification
CAR2
CAR5
50
PHA CAR2/CAR5
3.0
2.0
1.0
0.0
0.0
1.0
2.0
0
3.0
4.0
5.0
6.0
7.0
Magnitude
-50
-100
0
20
40
60
80
100
c)
120
Amplification
Time (s)
Iam ax CAR2/CAR5
5
4
3
2
1
0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Magnitude
 Site response relative amplification: soft soil sites
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Graduate Institute of Applied Geology
Data
Analysis
PHA amplification vs event magnitude
PHA CAR2/CAR1
4.0
3.0
2.0
b)
1.0
0.0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Magnitude
PHA CAR2/CAR4
Amplification
7
Amplification
Amplification
a)
4.0
3.0
2.0
1.0
0.0
0.0
6
5
PHA CAR2/CAR5
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Magnitude
4
3
2
1
0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Magnitude
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Data
Analysis
Arias intensity amplification vs event magnitude
Iam ax CAR2/CAR1
5
4
3.1
3
1
0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Magnitude
Iam ax CAR2/CAR4
Amplification
c)
2
Amplification
Amplification
b)
5
4
3
2
2.5
1
0
0.0
40
35
30
25
20
15
10
5
0
Iam ax CAR2/CAR5
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Magnitude
22.6
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Magnitude
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Data
Analysis
ELLIPTICITY VS EVENT MAGNITUDE &
Ia max

Ia min
ELLIPTICITY VS EPICENTRAL DISTANCE
CAR2
CAR3
5
Ia ellipticity
Ia ellipticity
4
3
2
1
0
0.0
1.0
2.0
3.0
4.0
5.0
6.0
20
18
16
14
12
10
8
6
4
2
0
7.0
0.0
1.0
2.0
3.0
Magnitude
Source
Effects
5
Ia ellipticity
Ia ellipticity
4
3
2
1
0
20
40
60
Distance (km)
5.0
6.0
7.0
Magnitude
CAR2
0
4.0
80
100
CAR3
20
18
16
14
12
10
8
6
4
2
0
0
20
40
60
80
100
Distance (km)
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Data
Analysis
A ri as i nte ns i t y am p l i fic at ion
v s e p i c ent re b ac k - azimut h
CAR2
CAR2 (without Aquilano events)
Ia_max Azimuth
CAR3
CAR3 (without Aquilano events)
35
14
Number of events
30
25
20
15
10
5
0
12
10
8
6
4
2
0
0
0
18
16
0
0
14
12
80
10
60
40
0
20
0
0
18
0
Ia_max Azimuth
16
0
0
14
12
10
80
60
0
40
0
Ia_max Azimuth
20
80
10
0
12
0
14
0
16
0
18
0
60
40
0
0
Number of events
5
80
10
0
12
0
14
0
16
0
18
0
10
60
15
40
20
0
25
10
9
8
7
6
5
4
3
2
1
0
20
Number of events
30
20
Number of events
35
Ia_max Azimuth
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Discussion and
Conclusions
HVSR RESULTS
CAR2
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Discussion and
Conclusions
CAR2: comparison HVSR (Horizontal-to-Vertical Spectral Ratios)
HVNR (Horizontal-to-Vertical Noise Ratios)
SSR (Standard Spectral Ratios)
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Discussion and
Conclusions
 There is evidence that seismic ground motion on slopes
covered by thick colluvia or by deep-seated landslides
can be considerably amplified and that in some cases this
amplification can have a pronounced directional character
with maxima oriented along potential sliding directions.
 The causes of the directivity phenomena are still unclear:
possibly a combination of topographic, lithological and
structural factors acts to re -distribute shaking energy,
focusing it on site-specific directions.
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Discussion and
Conclusions
 Limiting the observations to few nearby and small
magnitude events can cause an underestimate of site
response amplification.
 The wide range of shaking energy amplification (1.4 –36.4)
observed for different events relatively to a reference
station on rock highlights the difficulty in quantifying local
amplification factors.
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波的傳導，根據Snell’s Law，在不同介質中情況
sin 𝑖 sin 𝑖′
=
𝑣
𝑣′
i
V
V’
I’
V’>V
此為討論建立於平行層狀構造上，但事實上地震波所經過的地
球內部應是呈現球狀層狀構造。
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回顧研究方向性文獻
場址效應：
方向性 (directivity) ：
提到方向性與地形無關：
Vidale et al.(1991) at Los Angeles
Bonamassa and Vidale (1991) at California ( 認為是非均質地質條件造成)
提到方向性與地形有關：
Squdich et al.(1996) at California (沿著最大坡面有方向性)
與山崩構造有關：
Xu et al.(1996) (透過模型發現沿著山崩滑脫面S波產生偏振現象)
其他：
Rial(1996)(波被滯留在山波內低速物質而產生放大)
Vahdani and Wikstrom(2002)(地震波通過基盤時產生傾斜)
Gallipoli and Mucciarelli(2007)(HVSR峰值方向與滑移方向相同)
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