ADVANCES AND PROBLEMS IN UNDERSTANDING THE
SEISMIC RESPONSE OF POTENTIALLY UNSTABLE
SLOPES
1. Dipartimento di Geologia e Geofisica, Universita` di Bari, Bari, Italy.2. Istituto di Ricerca per la Protezione Idrogeologica, ConsiglioNazionale delle Ricerche, Bari, Italy.
Vincenzo Del Gaudio1 and Janusz Wasowski2
報告者:林子翔指導教授:李錫堤報告日期:01/06
National Central UniversityGraduate Institute of Applied Geology
SEISMIC RESPONSE
Seismograph
Source effect
Site effect
Path effect
Picture from :大地地理雜誌
National Central UniversityGraduate Institute of Applied Geology
September 19, 1985
SITE EFFECTS
October 17, 1989May 20 & November 15,1986
National Central UniversityGraduate Institute of Applied Geology
1. Why are we studying the site eff ects on unstable slopes?
2. What conditions will the site eff ects happen?
3. What will happen cause by site eff ects?
4. Our comprehension from previously studies in this problem
5. The expect of improvement and breakthrough through this study
Research motive
National Central UniversityGraduate Institute of Applied Geology
The influence of site eff ects on landslide triggering during earthquakes has been inferred in several studies, but its evaluation is made diffi cult 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.
ACCELEROMETRIC MONITORING OF CARAMANICO LANDSLIDE-PRONE
SLOPES.
Research motive
National Central UniversityGraduate Institute of Applied Geology
ORFENTO AND ORTA RIVER VALLEYS
high reliefactive river erosionstrong permeability
contrasts between diff erent lithologies
abundant rainfallclose to active seismogenic
structuresa case triggered by an event
that was quite far away (with epicentral distance more than 100 km)
ROMA
Study Area
National Central UniversityGraduate Institute of Applied Geology
Orfento river
Orta
river
Maiella Mts.
Alto hill
Caramanico Terme
Orfento River
CARAMANICO
0 100 m
M p
Lm
Lm
Lm
Bq
b
M p
sh
M p
1
2
3
4
5
N
LegendLm = 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; 5 = spring.
Caramanico Terme
Mt. Morrone
Study Area
1 km
CAR2
CAR1
CAR3
CAR4CAR
5
2002.10.10
2002.11.06
2004.12.03 2005.11.
11
2006.03.27
Accelerometric monitoring of a landslide-prone slopes at Caramanico Terme (Central Italy)
Study Area
accelerometric network
地質年代 (百萬年 ) 岩性代號 英文 岩性第四紀 (1.8-today) Bq Quaternary limestone megabreccias 石灰質火山角礫岩
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 泥岩第三紀中新世晚期 (7.246–
5.332)Me Messinian sandy-silty deposits with carbonate
breccia粉砂沉積物混和碳酸鹽質角礫
岩第三紀中新世 (23-5.3) Lm Miocene 石灰岩
未確認年代 L(m) limestones of uncertain Miocene age 石灰岩
Study Area
= accelerometric stations.
= microseismic noise measurements.
CAR4
CAR1
CAR2
CAR5
CAR3
National Central UniversityGraduate Institute of Applied Geology
Geologic profiles
Car1
Car2
Car3Car4
Car5
Study Area
WEAK GROUND MOTION DATA
NO. Launched
Car1 2002
Car2 2002
Car3 2004
Car4 2005
Car5 2006
Molise 2002 mainshock
2002-2008 82 152 2 5.7 161 km Period N. ev. N. record M>4 & N. rec >1 Max Mag Max Dist.
Data Acquisition
National Central UniversityGraduate Institute of Applied Geology
L’AQUILA EARTHQUAKE OF 6 APRIL 2009 (MW = 6.3)
Data Acquisition
National Central UniversityGraduate Institute of Applied Geology
Molise 2002 mainshock
L’Aquila 2009 mainshock
Period N. ev. N. record M>4 & N. rec >1 Max Mag Max Dist.
Up
North
East
Up
North
East
CAR1 recordings
2002-2008 82 152 2 5.7 161 km2009-2010 119 332 14 6.3 149 km
L’Aquila earthquake of 6 April 2009 (MW = 6.3)
Data Acquisition
WEAK MOTION DATA2002-2008
CAR1 VS CAR2
2002.11.12 09:27:49 East
-6
-4
-2
0
2
4
6
0 10 20 30 40 50
Time (s)
Acc
eler
atio
n (
gal
)
CAR2CAR1
Amplification (16 events)
PHA(gal) Ia(m/s)
Average 1.36 1.88Min 0.83 1.06Max 1.83 3.62
CAR2 (landslide site)
CAR1 (substratum outcrop)
Data Analysis
CAR3 VS CAR4
2006.06.05 00:07:50 East
-15
-10
-5
0
5
10
15
0 10 20 30 40 50
Time (s)
Acc
eler
atio
n (
gal
)
CAR3CAR4
CAR4 (reference)
CAR3 (on breccias)
Amplification (18 events)
PHA(gal) Ia(m/s)
Average 1.02 0.65Min 0.30 0.20Max 4.75 1.68
Data Analysis
National Central UniversityGraduate Institute of Applied Geology
Arias(Arias, 1970), 所定義 AI 之公式如下:
其中 g 為重力加速度( m/sec2 ); Td 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/sec2 ), AI 單位為( m/s )。
(corrected for the instrument response with 20 Hz cut-off frequency)
Calculate the Ia
Research Method
National Central UniversityGraduate Institute of Applied Geology
ellipticity ratio :the ratio between maximum and minimum of Ia values measured along horizontal directions at different azimuths.
Polar diagrams and Calculate the ellipticity
ratio
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.
min
max
Ia
Ia
Research Method
National Central UniversityGraduate Institute of Applied Geology
amplification :
1. The dynamic response of Car2 compare with Car1,an average relative amplif ication by a factor of 2.2 in total shaking energy.
2. At the site CAR2 constantly high ell ipt icity values were found, with all the Ia maxima oriented within a narrow azimuth interval around the local maximum slope direction.
PRELIMINARILY STUDY
Support:
Preliminary measurements of S-wave velocity with the technique of refraction microtremor analysis [Louie, 2001] gave values of 300–600 m/s for the landslide material and 1000–1500 m/s for the mudstone. At CAR3 a contribution to amplification likely derives from both topographic effect and impedance contrast between the carbonate breccias and underlying limestones.
Site Effects:
Hypothesis :
The relative amplification at CAR2 was attributed to impedance contrast between the colluvial (landslide) deposits and the underlying mudstone.
Discussion and Conclusions
POLAR DIAGRAMS OF NORMALIZED ARIAS INTENSITY
Max,0.99,260°
Min,0.55,170°
Max,0.90 ;min,0.83
Max,0.89 ;min,0.59
Max,0.96,290°
min,0.33,200°
Data Analysis
National Central UniversityGraduate Institute of Applied Geology
site eff ect evaluations by reference site method and non-reference sitemethod
SITE EFFECT EVALUATIONS
Reference site method
HSS=Horizontal Spectrum of Sedimentary site
HSR=Horizontal Spectrumof Reference site
HNS=Horizontal Noise of Sedimentary site
HNR=Horizontal Noise of Reference site
Borcherdt(1970)
Non-reference sitemethod
HNS=Horizontal Noise of Sedimentary site
VNS=Vertical Noise of Sedimentary site
HSS=Horizontal Spectrum of Sedimentary site
VSS=Vertical Spectrum of Sedimentary site
Lermo and Chávez-García (1993)Nakamura(1989)
Research Method
CAR1
(15 events)
CAR2
(14 events)
CAR3
CAR4
(7 events)
Horizontal - to -Vertical Spectral Ratio (HVSR) from seismic “weak motion” data until 2008
(19 events)
POLAR DIAGRAMS OF HVSR
Data Analysis
National Central UniversityGraduate Institute of Applied Geology
Site Eff ects :
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 eff ects, and hence its recognition requires the analysis of several recordings of events with sources located at diff erent station-epicentre back-azimuths and having diff erent focal mechanisms.
DIRECTIVITY
Discussion and Conclusions
STRONG MOTION DATA
2009L’AQUILA EARTHQUAKE
National Central UniversityGraduate Institute of Applied Geology
PRELIMINARILY STUDY
c) Iamax CAR2/CAR5
0
1
2
3
4
5
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Magnitude
Am
plif
ica
tio
n
b) PHA CAR2/CAR5
0.0
1.0
2.0
3.0
4.0
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Magnitude
Am
plif
ica
tio
n
2009.04.06 01:32:26 East
-100
-50
0
50
100
0 20 40 60 80 100 120
Time (s)
Acc
eler
atio
n (
gal
)
CAR2CAR5
Site response relative amplifi cation: soft soil sites
Data Analysis
National Central UniversityGraduate Institute of Applied Geology
PHA amplification vs event magnitude
b) PHA CAR2/CAR5
0.0
1.0
2.0
3.0
4.0
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
MagnitudeA
mp
lific
ati
on
a) PHA CAR2/CAR1
0.0
1.0
2.0
3.0
4.0
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Magnitude
Am
plif
ica
tio
n
Data Analysis
PHA CAR2/CAR4
0
1
2
3
4
5
6
7
1.0 2.0 3.0 4.0 5.0 6.0 7.0
Magnitude
Am
plif
ica
tio
n
National Central UniversityGraduate Institute of Applied Geology
c) Iamax CAR2/CAR5
0
1
2
3
4
5
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
MagnitudeA
mp
lific
ati
on
b) Iamax CAR2/CAR1
0
1
2
3
4
5
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Magnitude
Am
plif
ica
tio
n
Arias intensity amplification vs event magnitude
Data Analysis
Iamax CAR2/CAR4
05
10152025303540
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Magnitude
Am
plif
ica
tio
n
22.6
3.1
2.5
National Central UniversityGraduate Institute of Applied Geology
CAR2
0
1
2
3
4
5
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Magnitude
Ia e
llip
tic
ity
CAR3
0
2
4
6
8
10
12
14
16
18
20
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Magnitude
Ia e
llip
tic
ity
CAR3
0
2
4
6
8
10
12
14
16
18
20
0 20 40 60 80 100
Distance (km)
Ia e
llip
tic
ity
CAR2
0
1
2
3
4
5
0 20 40 60 80 100
Distance (km)
Ia e
llip
tic
ity
min
max
Ia
Ia
ELLIPTICITY VS EVENT MAGNITUDE &
ELLIPTICITY VS EPICENTRAL DISTANCE
Data Analysis
Source Effects
National Central UniversityGraduate Institute of Applied Geology
Arias intensity amplifi cation vs epicentre back-azimuth
Data Analysis
CAR3
0
5
10
15
20
25
30
35
Ia_max Azimuth
Nu
mb
er o
f eve
nts
CAR3 (without Aquilano events)
0
2
4
6
8
10
12
14
Ia_max Azimuth
Nu
mb
er o
f eve
nts
CAR2
0
5
10
15
20
25
30
35
Ia_max Azimuth
Nu
mb
er o
f eve
nts
CAR2 (without Aquilano events)
0123456789
10
Ia_max Azimuth
Nu
mb
er o
f eve
nts
National Central UniversityGraduate Institute of Applied Geology
HVSR RESULTS
CAR2
Discussion and Conclusions
National Central UniversityGraduate Institute of Applied Geology
CAR2: comparison HVSR (Horizontal-to-Vertical Spectral Ratios)HVNR (Horizontal-to-Vertical Noise Ratios) SSR (Standard Spectral Ratios)
Discussion and Conclusions
National Central UniversityGraduate Institute of Applied Geology
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 stil l unclear: possibly a combination of topographic, l ithological and structural factors acts to re-distribute shaking energy, focusing it on site-specific directions.
Discussion and Conclusions
National Central UniversityGraduate Institute of Applied Geology
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.
Discussion and Conclusions
The End
National Central UniversityGraduate Institute of Applied Geology
波的傳導,根據 Snell’s Law ,在不同介質中情況
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。
V
V’
i
I’
V’>V
National Central UniversityGraduate Institute of Applied Geology
National Central UniversityGraduate Institute of Applied Geology
National Central UniversityGraduate Institute of Applied Geology
場址效應: 方向性 (directivity) :提到方向性與地形無關:Vidale et al.(1991) at Los AngelesBonamassa 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 )
回顧研究方向性文獻