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Microtremor Analysis Using HVSR Method for
Microzonation Mapping of Earthquake Prone Areas in Klaten
District, Central Java
Rizqi Prastowo1
, Melfa Utari1
, Fitri Puspasari1
, Rita Desiasni1
, Rizka Anggraini1
,Achmad Nabil Zulfaqar2, Muhammad Rizki Fitraldi2
1Master Program of Geophysical, Universitas Gadjah Mada, Indonesia2Bachelor Program of Geological Engineering, Universitas Pembangunan Nasional Veteran
Yogyakarta, Indonesia
Email :[email protected] [email protected]
Abstract. Klaten District is one of districts in Central Java that on 27 May 2006 were affected
by powerful earthquake (also known as Bantul Earthquake) with a moment of magnitude 6,3
Richter scale based on (USGS, 2006). The shock occurred by the movement Opak Fault, where
located in Yogyakarta , with a distance of 40 km south-southeast from Klaten District. Based
on Indonesian Social Ministry, more than 18.000 people injured and 90.000 houses damaged.Therefore, mitigation steps are needed such as the distribution of earthquake prone
microzonation to reduce a risk that will occur in Klaten District. This microzonation is using
microtremor analysis then processed by HVSR method. Datas was collecting on 31 points
which cover the area of 67 km2. Based on analysis using HSVR method, value of quake
vulnerability obtained range 4,92-2489, the value of land amplification between 2,48113 -
21,4151, the value of natural frequency between 0,1842 1,7808 Hz and a maximum ground
acceleration values between 6,55 31,74 gal. From these result, Klaten District could be
divided into 2 earthquake prone microzonation. That is area with MMI VI-VII index in Central
Klaten Sub-district and Kalikotes Sub-district also the area with MMI
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There are several factors should be considered such as consisted lithology, hydrological condition, and
peak ground acceleration (Seed and Idris 1971). Generally, the lithologies in Klaten areas consisted by
volcanic deposits and alluvial deposits (soft sediment). These lithologies if passed by the earthquakewaves will tend to reinforce the wave, thus making the area a high risk of damage. Therefore, a study
on the potential hazards of earthquakes in a region is important.
One effort that could be done is to divide the earthquake-prone areas in detail. The measurement
microtremor using HSVR method could be done HVSR microtremor measurement method can be
done for these activities. The result is the value of natural frequency (fo), soil amplification (Ao), soil
vulnerability index (kg), and peak ground acceleration (PGA) microzonation . Study of this
microzonation is limited only to the coordinates x: 452000-462000 and y: 9143000 - 9152000.
Figure 1. Map location of study area
2. Methodology
The process of data collection is divided into two phases: survey design and data collection stage
microtremor. In the design phase of the survey, the study area includes Ngawen Sub-district,
Kebonarum sub-district, Northern Klaten Sub-district, Southern Klaten Sub-district, Wedi Sub-district,
Gantiwarno Sub-district and Kalikotes Sub-district. Data retrieval of microtremor measurements
obtained from 31 points of data retrieval locations by the distance between the point about 1-2 km.
Seismometer Short Period Tools Lennartz LE-3D is used in microtremor measurements with long time
70-75 minutes at each measurement point. Then data of Microtremor measurement is processed by
geopsy software with HVSR method to determine the value of natural frequency and amplification
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values could be calculated so that the value of land vulnerability and the acceleration of ground motion
could obtained.
Figure 2.Research flow diagram
3. Result and Discussion
Natural Frequency
Theoretically magnitude or frequency of the vibration period of soil or rock is a reflection of the
physical condition of the soil or rock. Soil or rock that is soft and loose rock will have a more compact
(Pusat Survey Geology, 2007). From the overall retrieval points obtained Fo value: 0.1842 with long
periods of vibration. The Softer rocks have a higher risk when shaken by earthquakes wave, because
of a greater amplification than 1.7808 Hz. Regions with high Fo value is in the south area of research.
Fo relatively uniform indicating the same rock lithology that consisted the area, which is material
deposit of Merapi.
Figure 3.Map of natural frequency (f0)
Soil Amplification
From whole retrieval points obtained values of Ao between 2.48113 - 21.4151. Great value ofamplification is located in the northeast area of research. Great value of amplification indicates that
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zone prone to earthquake vibrations. Because the greater value of Ao, the tremor with a certain
frequency that pass through the area will be amplified greater.
Figure 4. Map of soil amplification
Soil Vulnerability Index
Vulnerability of land in Klaten area has a value of 4.92 - 2489. The higher Kg, indicates the area more
vulnerable to earthquakes. Kg max value in the northeast area of research that indicates areas are
relatively more vulnerable if hit by an earthquake in compare airfares with other regions.
Figure 5. Map of Soil Vulnerability Index
Peak Ground Acceleration (PGA)
From the results of data processing in Klaten area values obtained Peak Ground Acceleration (PGA)
from 6.55 - 31.74 gal. Highest PGA located in the south of the research area which covers Central
Klaten Sub-districts and Kalikotes Sub-district.
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Figure 6. Map of Peak Ground Acceleration
Theoretically, the peak ground acceleration is the impact of earthquake waves at the measurement
location, so it could be a measure of earthquake intensity experienced. Based on PGA Klaten District
data could be divided into two categories the level of risk that the Central Klaten sub-district and
Kalikotes Sub-district included in the category of small risk to the value of the acceleration 25-50 gal
and intensity VI-VII whereas for the Ngawen sub-district, Kebonarum Sub-distict, Northern Klaten
Sub-district, Southern Klaten Sub-district, Wedi Sub-district, and the Gantiwarno Sub-district includedin very small category of risk with the acceleration values
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Acceleration (PGA). Simply microzonation illustrates grouping regions based on a risk level to the
earthquake region. Where in Klaten district, the Central Klaten Sub-district and Kalikotes Sub-district
included in the category of less risk with intensity VI-VII whereas for the Ngawen sub-district,Kebonarum Sub-distict, Northern Klaten Sub-district, Southern Klaten Sub-district, Wedi Sub-district,
and the Gantiwarno Sub-district in very small category of risk with intensity
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6. Acknowledgments
This microzonation in Klaten district is expected to help goverment and local community to mapping
the city from the possibility of earthquake and build awareness the importance of disaster mitigation.
But for now this microzonation not covered all of Klaten District. So it is expected to further research
can cover the whole of the district klaten and can complete the data from previous studies that still has
not been reached.