Seismic microzonation of hamirpur city using microtremor measurements
1. SEISMIC MICROZONATION OF HAMIRPUR CITY
USING MICROTREMOR MEASUREMENTS
CENTRAL UNIVERSITY OF HIMACHAL PRADESH
Master of Science in Environmental Science
Submitted by: Pandit Prashant Shera
CUHP18ENV18
Submitted to: Prof. Ambrish Kumar
Mahajan
2. INTRODUCTION
The effect of natural disasters have been increasing multifold in the past
few decades due to geological and meteorological hazards especially in
developing countries. These disasters causes heavy damage to
infrastructure, loss of life and termination of the development practices.
Man tries to reduce the impact of the natural disasters by technological
advancement and developing early warning system.
An earthquake is one of the worst natural disasters that may cause
devastating damage in a short period of time
In the present study, geophysical instrument i.e microtremor
system(tromino/tromograph) have been utilized for subsurface
characterization in Hamirpur city of Himachal Pradesh to estimate
ground motion characteristics, stiffness parameters of soil that will help
to modify existing building code of the area for effective disaster
management.
3. STUDY AREA (HAMIRPUR)
Hamirpur is town and headquarters of hamirpur district of himachal
Pradesh, located in the lower west central outer Himalayas.
District is situated between 31°25’ and 31°52 north latitude and
between 76°18’ and 76° 44’ east longitudes.
4. GEOLOGY AND GEOMORPHOLOGY OF HAMIRPUR
Almost the whole district is underlain by tertiary formations, represented by Shivalik group
of rocks (lower, middle and upper)
Lower Shivalik constitutes of massive dark gray sandstone and purple shales which are
overlain by micaceous sandstone and gray clay/shales of middle Shivalik.
Upper Shivalik comprises of coarse grained sandstones conglomerates, inter bedded with
grey and pink clays/slits and stans stones or pebbles beds
AGE FORMATION LITHOLOGY
Post-tertiary
(Quaternary)
Alluvium Sand, Gravel, Pebble & Boulders and
clay
Tertiary
upper Conglomerates, Boulders and pebbly
sandstone
middle Micaceous sandstone and shale
lower Hard, purple sandstone & shale
5. OBJECTIVES OF STUDY
• Learning methodology of microtremor data acquisition, its analysis and
processing by using GRILLA SOFTWARE.
• To find out predominant frequency from h/v spectral ratio, of different sites up
to bedrock level.
• To estimate ground motion characteristics and sesimic microzonation
• To get information about soil vibrations properties of sites,
6. METHODOLOGY
The site characterization of hamirpur city has been carried
out using microtremor system (tromino/tomograph). The
microtremor system was installed to record ambient noise
from 5 sites in the hamirpur city.
To derive natural/predominant frequency (fₒ) of different
sites up to the bedrock level microtremor system has been
utilized
The predominant/natural frequency(fₒ) is related to the
maximum amplitude of the ground motion in frequency
domain. The proximity of predominant frequency (fₒ) of the
soil and buildings brings higher vulnerability to the built
environment in strong motion excitation.
The tromino was utilized in passive mode for ambient noise
measurement to deduce fundamental/predominant/natural
frequency (fₒ) and amplification (A)
The Horizontal To Vertical Spectral Ratio Analysis (H/V) leads
to the computation of predominant frequency of each site,
which was further used to derive of sediment thickness
above bedrock.
7. METHODOLOGY
INTRODUTION TO TECHNIQUE
AMBIENT NOISE/MICROTREMOR MEASUREMENT
The ambient noise is related to seismic tremor, commonly called seismic noise,
exists even at the quietest site on earth.
The noise in frequency range of < 2Hz was produced from the natural sources like
the ocean and atmosphere, while the noise > 2Hz was produced from
anthropogenic sources like traffic and footsteps
The noise was recorded using tromino seismometer. The instrument works in the
frequency range from 0.1Hz to 1024Hz. The ambient noise measurement is a
passive data collection that provides a non-invasive recordings of seismic noise in
three orthogonal directions (N-S, E-W, and UP-DOWN) to derive predominant
frequency (fₒ) and amplification (A) through HVSR analysis.
8. METHODOLOGY
DATA ACQUISITION USING
MICROTREMOR SYSTEM (TROMINO)
The ambient noise measurement was
performed at 5 sites, within the Hamirpur city
using tromino seismometer.
Better coupling of the instrument was
ensured by fixing tromino with three long
spikes in a pit to avoid any interference from
direct wind and footsteps.
The data is acquired for 20 minutes at the
sampling frequency of 128Hz, which is
consistent with sesame criteria (SESAME
2004).
Location of study sites within Hamirpur city
9. METHODOLOGY
DATA ANALYSIS
The data was collected by running the
Tromino instrument for 20 minute and
later the data was imported and analyzed
using GRILLA SOFTWARE to obtain
Horizontal to Vertical Spectral Ratio
(HVSR) curve.
During data processing frequency range
of 0.2-64Hz was selected and were
computed using a triangular window with
10% smoothening and corrected for
sensor transfer function.
HVSR analysis showed that most of the
SESAME criteria for reliable H/V curve
and clear H/V peak are fulfilled
10. RESULTS
SITE-A
GOVERNMENT DEGREE COLLEGE
HAMIRPUR (synthetic track)
This site is located north of Hamirpur
city. The latitude and the longitude of
the site is 32⁰42’08.89”N and
76°31'13.39"E.
H/V ANALYSIS
The ambient noise spectrum shows
maximum peak at around 9.0Hz having
high impedance contrast due to
presence of alluvium fan deposits of
sand, gravel, pebbles and clay of post
tertiary age
11. RESULTS
SITE B
HPPWD CIRCUIT HOUSE GROUND
The site located in northwest of
Hamirpur city. The latitude and the
longitude of the site is 31°41'35.79"N
and 76°30'52.25"E.
H/V ANALYSIS
The ambient noise spectrum shows
maximum peak at around 26.25Hz
having no impedance contrast but
presence of hard rock, pebbly
sandstone and boulders
12. RESULTS
SITE C
KENDRIYA VIDHALAYA HAMIRPUR
(ground)
This site is located northwest of
Hamirpur city. The latitude and the
longitude of the site is 32⁰41’53.39”N
and 76°30'27.03"E.
H/V ANALYSIS
The ambient noise spectrum shows max
peak at 15.31Hz having high impedance
contrast due to presence of hard
sandstone and shale of tertiary age at
shallow depth.
13. RESULTS
SITE-D
POLICE LINE COLONY HAMIRPUR
(ground)
This site is located southeast of
Hamirpur city. The latitude and the
longitude of the site is 32⁰40’26.56”N
and 76°31'38.67"E.
H/V ANALYSIS
The ambient noise spectrum shows
maximum peak at around 12Hz. having
low impedance contrast due to
presence of weathered to hard rock of
micaceous sandstone and shale
14. RESULTS
SITE-E
GOVERNMENT POLYTECHNIC HAMIRPUR
(ground)
This site is located southeast of Hamirpur
city. The latitude and the longitude of the
site is 32⁰40’46.21”N and 76°32’21.91"E.
H/V ANALYSIS
The ambient noise spectrum shows
maximum peak at around 7.70Hz having
low impedance contrast due to presence of
conglomerates, pebbly sandstone and
boulder at shallower depth.
15. CONCLUSION AND RECOMMENDATION
The Nakamura technique has a large number of applications: besides its well-
known use for microzonation purposes.
Microtremor HVSR methods have been proven to be a good and fast,
economically feasible method in free field to estimate local site amplification in
terms of HVSR peak amplitude with a similar predominant peak frequency, but at a
different site amplification level to the site response analysis
According to the result and observation, area is having soft soil cover
that is prone to site amplification during earthquake hazard. Soft soil will amplify
low- frequency bedrock motion more than stiffer soil and reverse will be observed
in higher frequency. Therefore, it shows that in this area there is mostly soft soil
cover with hard rock at deeper depth. HVSR provides a good estimate of the
natural frequency of resonance of layered sediments.
Also, the accuracy of the measurements, reliability and clarity of the
peak in the H/V curve have been checked by SESAME guidelines. As final
conclusion, it is possible to say that, microtremor analysis using the Nakamura
technique proved to be a valuable tool to determine peak frequency and
amplification factor of shallow soft soils with simple layer distribution
