10th International Workshop of Seismic Microzoning and Risk Reduction
September 25, 2013, Tokyo, Japan

Microzonation Study in the Hanoi,Vietnam
K. L. Wen1, 2, C. M. Lin2, C. H. Kuo2, N. H. Phuong3, and N.
T. Hung3
1. Dept.
1
D t off Earth
E th Sciences,
S iNCU,NCU Taiwan
Ti
2. NCREE, NARLabs, Taiwan
3 IGP,
3.
IGP VAST,VAST Vietnam

Hanoi
Capital of Vietnamz Center of the Red River
triangular basinz Area 920.97 km2
z Population over 3millionz

Geology
Surface geology is mostly
sand and clayy sedimentaryyof Holocene or Pleistocene
z The bottom of Holocene
deposits is at the depth of
10 ~ 45 m
z The bottom of Pleistocene
deposits that overly theNeogene deposits is at thedepth of 45 (north) ~ 110(south) mzSeismicityz

Red-River fault zone isth mainthei tectonic
t t i activity
ti itof South East Asia
region The slip of theregion.
fault zone is right lateralwith normal fault
component. It caused themajor
j tectonic featuresin northern Vietnam.

Works in this study
1st Phase (2008~2009):
z 75 single-station microtremor measurements⇒ Site response of H/V spectral ratios
z 4 microtremor arrays⇒ Near-surface shear-velocity modelz Simulations of H/V spectral ratios⇒ Detail subsurface shear-velocity structure
2nd Phase (2012~2013):
z DenseDmicrotremoritsurvey⇒ Total 700 single-station microtremor points⇒ 4 more microtremor arraysz Microzonation⇒ Vs30 distribution⇒ Seismic microzonation

Microtremor H/V Spectral Ratio (75 points of 1st phase)

Apparent dominant frequency ofseismic site effectDominant Frequency of H/V ratios (0.8 ~ 2.0 Hz)

Microtremor Array (4 arrays of 1st phase)

0.030

0.020

Freq enc Wa en mber method (F-K)
Frequency-Wavenumber(F K) ：0.010

-0.030-0.020-0.010

0.000
0.000

-0.010-0.020-0.030

0.010

0.020

0.030

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,96m 0.5~2.0Hz
0 5~2 0Hz (only for HA2)

Maximum Likelihood Method ofFrequency Wavenumber (FFrequency-Wavenumber(F-K)
K) Analyses
F KS
F-KSpectra
t2Hz

3Hz

4Hz

6Hz

Inversed Near-Surface
Vs Models

HA1

HA2

HA4
HA3Di
Dispersion
i CurvesC

Simulations of H/V Spectral Ratios
Simulating the microtremor H/V spectra ratios to estimate theVs model of the 75 points based on the theoretic SH-wave
transfer function (Haskell,(Haskell 1960)z The initial 8-layer model was decided by the inversed modelsof the arrays in Hanoi. And the averaged Vs were used as thefixed Vs to estimated the thickness of each stratumz

1D Vs Model for 75 sites

Main Interface of the Vs Structure
VS > 0.5 km/sec

VS > 0.8 km/sec

Comparable with the bottomof Holocene deposits which isat the depth of 10 (north) ~45 (south) m

Comparable with the bottomof Pleistocene deposits which
is at the depth of 45 (north) ~110 (south) m

Dense Microtremor Survey (2nd phase)zDense survey, especiallyat urban region, isnecessary to provide
detail site information forseismic microzonation
and risk assessmentz

Total 700 single-station
microtremor points and 4more arrays werecompletedDominant Frequency of Dense Microtremor Survey

Seismic Microzonation of Hanoi

Vs30 Map of Hanoi
All the H/V spectral ratios
were simulated to estimate
the Vs models andcalculatel ltheh seismic site
conditions (Vs30).
z Vs30 decreases from North
to South in Hanoi
z The highest Vs30 is moreththan
300300m/s/ ini thethnorthern part. The lowest
Vs30 is less than 180 m/s/in the southern part,
including a part of theurban region.
regionzConclusions
 The dense microtremor surveys, including 700 single-station

measurements and array measurements at 8 sites,
sites have been
conducted in Hanoi region.
 H/V spectral ratios in Hanoi region show an apparent dominantfrequency between 0.8 and 2.0 Hz. It was proved that theapparent site amplification is dominated by the thicknesses ofnear-surface deposits.
 All the observed microtremor H/V spectral ratios were simulated
to figure out the overall detail subsurface Vs structure in Hanoi
region.
 According to the site characteristics and Vs structure, the seismic
micro onation and Vs30 map of Hanoi weremicrozonation
ere accomplished toprovide the site information for the seismic risk assessment.

Strong motion station: 69
500 stations
I t
Intervall ~ 1 kmkLocations of the microtremor survey points in the Taipeiarea. Red
R d symbols
b l iindicate
di t ththe strong
tmotionti stations.
t ti

Dominant frequency contour in the Taipei basin area,
result from the H/V ratio of dense microtremor survey

0 5 Hz0.5

2 0 Hz2.0H/V spectral ratio contours at 0.5 and 2.0 Hz.

H/V spectral ratio contour
at 0.5 Hz.

Sungshan Formation Bottom--- Taipei Basin2011.1修訂後公告之臺北盆地設計地震微分區圖
Microzonation Map of Taipei Basin in the Building Code Modified on 2011.

Thanks for your attention!
wenkl@earth ncu edu tw
wenkl@earth.ncu.edu.tw