Note: This Information Product is a first attempt to provide guidance in preparing the information needed for the CLUP. As more knowledge is gathered, the IP will be updated. Likewise, updates may be required due to new or changing land-use policies. Furthermore, data will continuously be prepared by the custodians, which may require updates.
For the latest update, please check HLURB Homepage: http://www.hlurb.gov.ph/ or contact HLURB: telephone +632 927 2698.
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| Step 1: Provide a Background and Identify the Objectives of the GIS Analysis | ||
| Hazards are great concerns for an LGU. Unlike flooding which can more or less be controlled, through flood control structures, the hazards illustrated here present permanent danger which is beyond the control of men.
A fault is a fracture in the Earth's crust along which two blocks of the crust have slipped with respect to each other. A fault may be active or inactive. An active fault is a fracture caused by an earthquake that has occurred within the last 100 years while an inactive fault is vice versa. An earthquake is a sudden rapid shaking of the earth caused by the breaking and shifting of rock beneath the earth's surface. Earthquakes can cause buildings and bridges to collapse, disrupt gas, electric and phone lines, and often cause landslides, flash floods, fires, avalanches, and tsunamis. Larger earthquakes usually begin with slight tremors but rapidly take the form of one or more violent shocks, and end in vibrations of gradually diminishing force called aftershocks. The underground point of origin of an earthquake is called its focus; the point on the surface directly above the focus is the epicenter. The magnitude and intensity of an earthquake is determined by the use of scales like the Richter scale and the Mercalli scale. Hazards that are associated with faults and earthquakes are liquefaction, earthquake induced landslides and tsunami. Active volcanoes are also risk areas if there is one in the municipality/city or in the vicinity. There is great danger to both property and lives whenever an eruption occurs. The permanent danger zone should be free from any structure and inhabitants to prevent loss of property and lives. Similarly, identified landslide prone areas should also be clear of inhabitants and permanent structures. It is also important that these be included in a dataset if there are any such areas in the municipality/city. Subsidence areas are areas where grounds are likely to fall which can endanger lives and properties. These are just some of the hazards that an area may have. Some agencies might have other datasets (fault lines (inactive), liquefaction, etc.) These areas should be likewise be investigated and their effects be discussed with experts (PHIVOLCS, NAMRIA, individual geologists, etc.) on how they can help the LGU planners include these in their plans. The information to be derived is not intended to scare aware investors but to provide information to LGUs and enforce necessary mitigating measures to manage disaster (for example through zoning, controlled development on affected areas, height requirements on buildings, additional safety features on structures, etc). The objective of this GIS analysis is to present the fault line areas/Earthquake prone areas, volcanic hazard, landslide prone and subsidence areas on the map as input to the Risk and Suitability Map. |
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| Step 2: Identify the Indicators to Evaluate Risk and Suitability | ||
| People living on steep slopes, or mountainous areas which may be in close proximity of an active fault. | ||
| People living in close proximity of an active volcano. | ||
| People who live or work in unreinforced masonry buildings built on filled land or unstable soil are more at risk | ||
| Step 3: Create the Database | ||
| Attribute | ||
| The following attribute tables may be used for this sector. Those in bold are used for the examples here.
EM05 Fault line |
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| The custodians for the data are the Philippine Institute of Volcanology and Seismology (PHIVOLCS), MGB and NDCC | ||
| Spatial | ||
| fault line |  |
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| volcano |  |
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| Step 4: Analyze the Data | ||
| The following Analyses layers can be prepared based on the Baseline Information: | ||
| There should be a buffer area of 5 m on both sides of a fault line where no development will be made. There is a possibility that fault areas are within urban areas, this will help identify these areas and plan what to do with them. | ||
| Existing built up areas prone to earthquakes (raster) | ||
| Not recommended areas for urban expansion due to earthquake hazards (raster) |  |
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| Step 5: Present the Data | ||
| The example below shows Active Fault lines passing through Agricultural and Forest lands. Direct effects of the fault line would be minimal since these areas are not so populated. However, surrounding areas will still experience the effects depending on the distance and magnitude of the earthquake. But scenarios should be made (with the aid of concerned agencies) to determine the impacts of these active faults in case an earthquake occurs, and the need for evacuation of residents. | ||
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| The next example shows faultlines directly affecting urban areas. A buffer of (250m) for the Fault lines was used for this example. | ||
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| Faultlines buffer overlaid with an aerial photo showing a densely populated urban area. This will give an idea on the possible impact when an earthquake occurs. | ||
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| Example below shows the 4 km Danger zone within active volcanoes. This area should be clear of inhabitants since they present permanent danger whenever the volcano is active. | ||
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| Attachment | Size |
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| 04.08.06_FaultEarthTsunamis.pdf | 733.77 KB |