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kinds of geological hazards are landslide, mountain eruption, earthquake,
flooding, erosion, salination, and drought Noor, 2006.
The types of geological hazard which have often been occurring are cause by four factors; soil movement, mountain eruption, debris avalanches, and earthquake
Noor, 2006. That kind of geological hazard is the main hazard which cause more property damage and death toll. In this research study, the focus is in geological
hazard caused by earthquake.
2.3.3 Earthquake
Earthquake is a shaking and trembling of the crust of the earth, caused by collision between ground plates, active fault from volcanic activity, and detritus of rock
BNPB, 2007. An earthquake is a sudden, rapid shaking of the earth caused by the breaking and shifting of rock beneath the earths surface Earthquake, 2007.
Earthquake is an energy released phenomenon that cause dislocation in the inside part of earth with instant change.
Refer to USGS 2008, term of earthquake is the vibration, sometimes violent, of the earths surface that follows a release of energy in the earths crust. This energy
can be generated by a sudden dislocation of segments of the crust, by a volcanic eruption, or event by manmade explosions.
The main causes of earthquakes BNPB, 2007 can be classified as follows: 1.
Tectonic activity caused by ground plate displacement. 2.
Fault activity in earth surface. 3.
Local geomorphologic displacement, for example soil detritus. 4.
Volcanic activity. 5.
Nuclear explosion.
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Figure 2.1 Illustration earthquake caused by tectonic activity Bakornas PB, 2007.
Earthquakes can occur at any time without warning. An earthquake sequence happen in the place where earthquakes occurred in the past and it will happen
again Earthquake, 2007.
2.3.4 Impacts of Earthquake
The impact of earthquake depends on many factors related to ground seismicity and activities on the surface. The factors depend on each other’s and it can
strengthen the earthquake. The most earthquake effect is building damage caused by ground shaking and trembling.
Refers to Bell Bell, 1999, the most serious direct effect of earthquake in terms of building and structures is ground shaking. Researchers prove ground condition is
a main factor shaking effect and it cause damaging for building and structures. Although building and structures standing on the firm bedrock, it can still be
affected, so the susceptible buildings should not be located near to a fault trace. The most effects caused by earthquake classify into 4 four types Upseis, 2008:
1. Ground Shaking
Buildings can be damaged by the shaking itself or by the ground beneath them settling to a different level than it was before the earthquake subsidence.
14 Figure 2.2
Friday earthquake in Anchorage, Alaska Walker, 1982
Figure 2.3 The ruins in Bantul,
Yogyakarta Province, 2006.
2. Ground Displacement
The second main earthquake hazard is ground displacement ground movement along a fault. If a structure a building, road, etc. is built across a fault, the ground
displacement during an earthquake could seriously damage or rip apart that structure.
3. Flooding
The third main hazard is flooding. An earthquake can rupture break dams or levees along a river. The water from the river or the reservoir would then flood the
area, damaging buildings and maybe sweeping away or drowning people.
4. Fire
The fourth main earthquake hazard is fire. These fires can be started by broken gas lines and power lines, or tipped over wood or coal stoves. They can be a
serious problem, especially if the water lines that feed the fire hydrants are broken, too.
2.3.5 Yogyakarta and Bantul Earthquake
Yogyakarta earthquake occurred on 27
th
May 2006, which destroyed all settlements and public facilities surrounding Yogyakarta. The strike hit not only in
Yogyakarta city, but it happened also in Bantul and Klaten regencies. Those areas have high density population, and affected to a number of death tolls.
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The epicenter Yogyakarta earthquake located in the west side of Opak fault line, which has geographic coordinate; 8.24º S and 110.43º E USGS, 2006 in Haifani,
. 2008. Alongside that coordinate is the central of damaging, which was through in Merapi alluvial materials formation. That formation are consists of
alluvial, tuff, breksi, agglomerate, and lava current Haifani, 2008.
Figure 2.4 Epicentrum Yogyakarta Earthquakes UNOSAT, 2006
The numbers of victims in Yogyakarta earthquake were 4,680 people killed, and 19,897 injured Table 2.1. The administrative area has a lot a number of death
tolls located in Bantul Regency with 4,141 people, that statistic is over than 90 percent all sum of dead people. Almost the dead victims were caused by struck
down of building materials.
Table 2.1 Victim Data in Yogyakarta Earthquake
No. Local Government
Victims Death
Injured
1. Bantul
4.121 12.056
2. Sleman
232 3.789
3. Yogyakarta
204 318
4. Kulon Progo
22 2.678
5. Gunung Kidul
81 1.086
Total 4.660
19.927
Source: Yogyakarta Earthquake Media Center 2006 in Haifani, . 2008.
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Yogyakarta earthquake also caused a lot of destruction of many houses in some area. Bantul has the highest number of damaging houses compared to other areas,
at least 96,360 houses were totally damaged totally loss, and 70,769 heavily damaged Table 2.2.
Table 2.2 Number of house damage in Yogyakarta Earthquake
No. Local Government
Number of House Damage Totally
Damage Heavy
Damage Light
Damage
1. Bantul
71.482 71.718
2. Sleman
5.243 16.003
3. Yogyakarta
7.161 14.535
4. Kulon Progo
4.527 5.178
5. Gunung Kidul
7.746 10.670
Total 96.159
118.104 156.568
Source: Yogyakarta Earthquake Media Center 2006 in Haifani, . 2008.
2.4 Methodology 2.4.1
Method of Research
The method of research mapping earthquake hazard is shown in figure 2.5. First part research method is to review and identify hazard potential factor. Those
factors were selected and examined by geological experts, which was explained in manual of spatial planning for mountain eruption vulnerability area, and
earthquake vulnerability area. Rock structure, slope and relief, earthquake intensity, and geological structure are the most affected when earthquake occurs.
Figure 2.5 Schematic diagram of ground stability mapping methodology
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2.4.2 Review and Identify Earthquake Hazard Criteria
There are many criteria related to earthquake hazard that can determine the level of damage. Most of the researchers believed the closeness to fault way were the
most important criteria in earthquake hazard Bell, 1999, ITC, 2005, BNPB, 2007, Erdik, 2007. Bell 1999 explained although a land had solid firm bed rock
wasn’t effect when in the land had or through fault way. Some experiences describe which higher damage area located near or precise in fault way.
Fault Way
Fault way is the vulnerable place when interCplate movement and intraCplate movement occur, which is divided into two categories; horizontal and vertical
movements Gulati, 2005 Figure 2.6. The movement plate in fault way is the primary threat, which causes ground shaking effect. The bigger intensity in
ground shaking cause higher damage for building and infrastructure Bell, 1999.
a Dip Slip Fault b Dip Slip Fault c Strike Slip Fault
Figure 2.6 Type of slip plate movement at fault Kadarisman Gulati, 2005
Earthquake Intensity
Second criterion which is important in earthquake hazard is earthquake intensity. Earthquake intensity is the function of magnitude, distance from epicentrum,
vibration time, earthquake deep, soil condition, and structure condition PIRBA. The measurement of earthquake intensity states in mercalli modified intensity
MMI. Earthquake intensity is closely related to another intensity criteria; gravity force α, and richter scale Table 2.3. Levels in MMI scale can be described as
follows in state earthquakes Table 2.4.
