Site Characteristic of Microtremor and Velocity Models in Hanoi

Site Characteristic of Microtremor and Velocity Models in Hanoi

TEM Workshop
IESAS, Oct. 7, 2011
Site Characteristic of Microtremor and
Velocity Models in Hanoi Region, Vietnam
K. L. Wen1, 2, C. M. Lin2, C. H. Kuo2 ,
J. Y. Huang1, C. T. Chen1
1. Institute of Geophysics, NCU
2. NCREE, NARL
2
Introduction


Hanoi, the capital of
Vietnam, lies at the center
of the triangular basin of the
Red River with a population
over 3 million people, and
an area 920.97 km2.
Red-River fault zone is the
main tectonic activity of
South East Asia region. The
slip of the fault zone is right
lateral with normal fault
component. It caused the
major tectonic features in
Vietnam, such as rifting and
folding.
3
Epicenters (1900~1995) and fault distributions in north
Vietnam (Xuyen, 1995)
4
Near-Surface Geology Profile
5/20
75 microtremor
measuring points
 4 sites of arrays

6
Vel. Microtremor
Microtremor
H/V Spectral Ratio
（Nakamura,1989）
Data cutting (8192 points)
windows selection
FFT
NS component
spectra
EW component
spectra
Horizontal
component
spectra
H/V ratios
Mean H/V ratios
Vertical
component
spectra
7
H17
H05
H70
H29
8
9
Dominant Frequency
The contours of H/V ratio
for varied frequency bands
10/20
Microtremor Array
0.030
0.020
0.010
-0.030
-0.020
-0.010
0.000
0.000
-0.010
-0.020
-0.030
Frequency-Wavenumber method (F-K) ：
Total time length: 70min
Window length: 1024, 2048, 4096 points
Moving window: 200 points
S array: 32m, 2.0~7.0 Hz
L array: 64m, 0.5~4.0 Hz
XL array: 96m, 0.5~2.0Hz (only for HA2)
0.010
0.020
0.030
11
N
12
E
13
14
Maximum Likelihood Method of FrequencyWavenumber (F-K) Analyses
F-K Spectra
Dispersion Curves
15/20
Inversed Near-Surface
Vs Models
HA1
HA2
HA4
HA3
16
The comparison between theoretic SH-wave transfer function
(black line) (Haskell, 1960) and Average H/V Ratio (red line)
for the four arrays
17
徵求2012年國科會與越南科技部（NSC-MOST）
雙邊共同合作計畫
2011/5
Site Effect Estimation and Urban
Seismic Risk Assessment for Hanoi City
(2012/1~2013/12)

Vietnam
Dr. Phuong Hong Nguyen, IGP, VAST
Mr. Nguyen Tien Hung,
IGP, VAST

Taiwan, ROC
Prof. Wen, Kuo-Liang,
Dr. Lin, Che-Min,
NCU
NCREE
18
 Near-surface
S-wave velocity structures
 Site information ( predominant frequencies,
Vs30, and near-surface S-wave velocity ) for
the seismic risk assessment
 Seismic risk assessment GIS tool concerning
the site variation provide rapid, accurate and
detailed seismic risk information
 Mitigate the potential damage and loss of life
due to future earthquakes
19
Site Effect Estimation (NCU, Taiwan)




Modeling the microtremor H/V ratios (Haskell & GA)
75 Near-surface S-wave velocity structures
Vs30 and the depths of main interfaces contour maps
Relation between the S-wave velocity and SPT-N value
20
Urban Seismic Risk Assessment GIS Tool
(IGP, VAST, Vietnam)
Fault – source model and
earthquake scenarios
 Dataset on building
inventory, population and
geophysical data
 GIS based tool for urban
seismic risk assessment
for Hanoi and Vietnam
 Pilot testing of risk
analysis and loss
estimation for a
downtown area

1 Define a
study region
2. Define an
earthquake
scenario
3. Ground
motion
assessment
4. Ground
failure
assessment
Demographic
data inventory
and
vulnerability
5.Damage
and loss
estimation
Decision making:
Earthquake disaster
reduction planning
 Preparedness
 Emergency response
 Recovery
Workshop on “Earthquake, Tsunami Hazards and
Early Warning System in the Asian-Pacific Region”
5-6 September, 2011, VAST, Hanoi, Vietnam
Workshop on "Risk Modeling, Predicting and
Mitigating"
Institute for Research Development, France and IGP,
VAST, 16~18 November, 2011, Hanoi
“Taiwan-Vietnam Bilateral Meeting”, 19~22
Nov., 2011, Hanoi
Prof. Tung-Yi Lee 李通藝
Dr. Anh (head of Institute of Geology, VAST)
21
TEM Workshop
IESAS, Oct. 7, 2011
Thank You For Your Attention!
wenkl@earth.ncu.edu.tw
H/V Spectra Ratio Simulation
（GA-Haskell method）


GA-Haskell method based on the combination of the
theoretic SH-wave transfer function (Haskell, 1960) and
Genetic algorithm (GA) simulates the microtremor H/V
spectra ratio to estimate the shear-velocity model of the
measuring point.
The fitness function of GA is defined by linear correlation
coefficient and dominant frequency.
r
 x
 x
i

 x yi  y
i
i

i
x
  y
2
i

y

2

FSH  FHV
 r  1
f 
  0.8  1 
0.3  FHV
 2 


  0.2


i
The initial 8-layer model was decided based on the inversed
models of the arrays in Hanoi. And the averaged shearvelocity were used to search the thickness of every layer.