Lembang Fault activity studies using GPS technology

Fault system (FAULT SYSTEM)

Plate boundaries in a smaller scale is known as a fault which is a boundary that connects two adjacent tectonic blocks [Puspito, 2000]. Field fault (fault plane) is a field which is the area of ​​contact between two tectonic blocks. Shifting the field of fault can range from between a few meters to reach hundreds of kilometers. Fault is a weak line, and occurs more frequently in layers of hard and brittle. The material was destroyed at the fault lines caused by the shift, can range from the gouge (a substance that is fine / fine due to friction) until the fault breccia, which has a thickness between a few centimeters to hundreds of meters (crushed fault zone width).

There are two elements to the fault of Wall hanging (the roof section) and Foot Wall (base section). Wall Hanging (roof fault) is that there is a fault blocks at the top of the field of fault, while the foot Wall (base section) is the fault blocks located at the bottom of the field of fault. Field faults formed as a result of cracks that shift.

  

 Judging from the position of fault against the surrounding rock structure (usually applied to a fault in the sedimentary rocks) (Asikin, 1978 in Puspito 2000), faults can be classified as follows:

  

 1) Strike Fault, which is the fault jurusnya direction parallel to the surrounding rock stance.

 2) Fault Dip, is the stance of the fault direction of the slope of the surrounding rock layers

 3) Diagonal or Faulting Oblique, is a fault that cuts the surrounding rock structure.

 4) Longitudinal Fault, the fault direction parallel to the main direction of the regional structure.

 5) Fault Traverse, is a section cut perpendicular / oblique to the regional structure

     (Usually found in the area folded, cut the axis of the anticline)

  

 Meanwhile, when viewed from genesanya, faults can be classified into several types as follows:

  

 1) Normal when the Hanging Wall Fault (fault roof) moves down relative to foot wall

 2) Fault Rise / lid when the Hanging Wall Fault (fault roof) move relative rise

     against Foot Wall (base section).

 3) Horizontal Fault / shear fault (Strike Slip Faulting), a separate move relative

     horizontally on the field of fault generally upright (90o).

Faulting RELATIONSHIP WITH EARTHQUAKES

Where is the usual occurrence of a natural earthquake is large enough, according to research results, the researchers concluded that the earth nearly 95 percent more earthquakes occurred in the boundary regions between Earth's crustal plates and faults in the region [Mori, 2004]. The earthquake that occurred in the fault area can bear a number of disasters, such as casualties, damage to various structures, avalanche, and others. The death toll could reach tens or even hundreds of thousands of lives and material losses could reach hundreds of millions of U.S. dollars.

Examples of the earthquake that occurred in areas such as earthquake fault that occurred in Thangsan China on July 28, 1976 claimed 240 000 lives, the earthquake happened in Iran in 1990 claimed 40,000 lives, and earthquakes occur Armenia in 1998 killed 25,000 people .

Faulting STUDY FOR MONITORING THE POTENTIAL FOR EARTHQUAKE DISASTER MITIGATION

Given the facts that show an earthquake fault may occur in the area and can provide large losses of both life and matter, then the step of monitoring potential earthquake as one form of mitigation efforts obviously important to be done to reduce the negative effects that can be left by disaster.

Geologically the area of ​​Indonesia will be found many faults (fault) which is an area that is prone to earthquakes. Examples of common faults for the research field of Earth is the fault of Sumatra (the Great Sumatran Fault), Palu Koro Fault in Central Sulawesi, Faulting and Fault Cimandiri Lembang West Java. Facts show has many records of natural disasters in the vicinity of earthquake faults like the Sumatra quake Liwa year 1932.1994, Kerinci earthquake 1909, 1995, which left the mental and material losses are quite large. Given this reality, the study of the potential for earthquakes in order to mitigate the obvious imperative to do in Indonesia.

Then exactly how the form of study can be done to see the huge potential of earthquakes following disasters? Here below is given an example of a model study of the earth's natural potential for earthquake disaster created by the U.S. National Government. To make this model combines components of their areas of study such as science and technology Seismicity, Paleoseismology, Local Site Effects, geologic Structure, Dynamic Rupture, Seismic Velocity Structure, Crustal deformation by InSAR, Crustal Motion by GPS, Stress Transfer, and Fault Information. By studying the fields of science and technology studies, and then integrate it, you will get how big the earthquake potential in the case study.

STUDY OF Lembang Fault

Lembang Fault is one of the most fascinating geological landmarks in the Highlands Bandung and a clear geomorphological expression of neotektonik activity in the Bandung Basin. Lembang Fault morphologically expressed in the form of escarpment fault (fault scrap) with the wall towards the north facing escarpment. Lembang Fault which parts can be seen, both from topographic maps or aerial photographs, especially from satellite imagery, has a length of 22 km. From east to west, the high escarpment that reflect the magnitude of the shift cesarean section (vertical jump / throw or dislocation) changed from about 450-meter at the eastern end (Maribaya, G. Pulusari) and 40-meter to the west (Cisarua) and then disappeared in the north west tip of Padalarang.

  

Geomorphic expression that distinguish the eastern section which is characterized by a steep escarpment to the west of the relatively less steep and disappeared in the West Cisarua, more detailed and easily identifiable geographically, divided right at the road-Lembang Bandung. In this area there is a flat area along the road to the city of Bandung, Lembang Lembang District. To the west of this narrow plain bounded by S. Cihideung wrenching spurs and deep, flowing north-south fault escarpment cut. To the east, fault escarpment is characterized by very steep cliffs with a relative height difference of 75 m in Lembang (West) to more than 450 m in G. Pulusari (east end) is the higher altitude due to vertical penyayatan (incise) volcanic deposits on its feet. While in the western escarpment fault is not so high and only reaches a height of 40 m in area relative Cihideung, Cisarua. In this section, fault escarpment covered with volcanic deposits younger.

Stone Mountain is one of the best location for observation of the Lembang Fault. Rock made up of igneous andestik. Lava flow is estimated as compassionate column shows the burly-burly that can be observed on the northern slopes. However, many geologists and geophysicists who have other opinions about the rock andestik in the Rock. Some expect it as an intrusion or volcanic neck, a few more suspect as the product of the eruption crack (fissure Eruption). The results of age dating by K-Ar method show that the rocks formed at Stone Mountain andestik 0.51 Ma (Sunardi and Koesoemadinata, 1997), or 510,000 years ago.

A relatively new research results from Nossin et al. (1996) suggests that the possibility of the first shift in Lembang Fault (in particular the formation of the eastern Lembang Fault) which coincides with the formation of the caldera in the cataclysmic eruption occurred 100,000 years ago. While the western part of the Lembang Fault diperkiakan younger than 27,000 years ago. This is caused by the presence of pyroclastic deposits which was unbroken by the fault.

The flow of lava broke through the wall of the eastern section through Ci Kapundung in Maribaya, but this does not happen in the east. Thus, the western section allegedly younger than phase-B van Bemmelen, but broke deposits van Bemmelen-C phase. Nossin et al. (1996) analyzed the dating of peat samples from Kampung Penyairan located at Lembang Fault valley in the west. The results of the analysis of K-Ar dating by Sumardi and Koeseomadinaa (1997) showed in the basalt lava waterfall Dago was 48,000 years ago, and old lava flows in Maribaya 150,000 years ago. Black basaltic lava is constantly from the upstream river Cikapundung (Maribaya) until ending around Curug Dago, estimated to consist of several "layers". If the fault is active in the west end about 24,000 years ago, so if the eastern part active, lava-lava should come broken, too.

Mount Tangkubanparahu appear on fault lines trending west-east, where most of the intrusion of magma have been frozen to form a dike. Weak zone located on the south and west, allowing the ongoing activity of Mount Tangkubanparahu today. Switching points of activity (crater) Mount Tangkubanparahu have a trend toward the east-west fault. Very prominent fault structures displayed by the residual magnetic anomaly pattern (Example: Faulting Lembang). Hot springs in Ciater, made possible due to the heating subsurface water derived from G. Tangkubanparahu flowing through the field of fault.

Study In Movement Geodetic Lembang Fault

 

 In early 2006, KK Geodesy in collaboration with the resource geologists began to re-examine the status of Lembang Fault characteristics by utilizing GPS technology. Earlier in cooperation with the University of Japan, which had conducted research in 1994-1998 and 2003. As it is known that the Lembang Fault lies not far from the city of Bandung is loaded resident. Therefore, research on this fault clearly necessary, because the region can have a potential earthquake fault. GPS technology can see the geometric characteristics of the dynamics around the fault, then can then be used as a parameter in the determination of fault activity model.

  

  

 The principle of fault activity determination using GPS survey method is by putting some points in some selected locations, periodically coordinates accurately determined using GPS survey methods. By studying the pattern and pace of change the coordinates of the points from the survey that one to the next survey, then along with other supporting data in mathematically modeling the characteristics of fault activity will be seen and studied further in order to manufacture models of potential earthquake . Models that can be made such as: elastic deformation model, which then shows the fault parameters such as fault location, fault geometry and the rate of accumulation of deformation on the fault. Then from this model we can determine the accumulated strain, locking depth, energy prediction earthquake that may occur in the fault area. In other words, through GPS data input and output models of fault activity, then we can determine the model of potential natural disasters in the earthquake fault that we examine.

  

 As mentioned above, previous GPS survey was conducted in the area surrounding Lembang Fault in the period 1994 to 2003. The data obtained can be combined with data to be taken in this research program to use as the main parameter in determining the pattern shift Lembang Fault.

The location and distribution of GPS points to study the activity of Lembang Fault by GPS deployed close to the fault and in some places far from the fault to see its far-field velocity. Monitoring net is later processed by including IGS data are scattered around Asia and Australia as a global binding points.

Characteristics of fault shifts obtained from GPS surveys in Lembang Fault This information will then be integrated with fault activity history, tectonic setting information to create models of potential earthquakes around the Lembang fault, and then the model is expected to assist mitigation efforts.

Posted in: EARTHQUAKES,Faulting