Types of faults
PHIVOLCS names three main types of fault movement: normal, reverse and strike-slip. For a household, the more useful question is whether a fault is active, which PHIVOLCS defines as having moved in the last 10,000 years and expected to move again.
This page belongs with the earthquake preparedness guide, which covers what to do before the shaking starts.
Written for the Philippines. In an emergency here, the number is 911.
What a fault is
PHIVOLCS defines faults as fractures in the Earth's crust where blocks of rock move relative to one another. A fault can be small and local, or hundreds of kilometers long.
Sudden movement along faults and plate boundaries is what produces a tectonic earthquake, one of the two kinds PHIVOLCS names. The other kind, a volcanic earthquake, comes from magma rising beneath an active volcano.
Source: PHIVOLCS, Earthquake Hazards. Read 23 October 2026.
Source: PHIVOLCS, Introduction to Earthquake. Read 23 October 2026.
The three types of fault movement
PHIVOLCS defines the first two by what the hanging wall does, relative to the footwall. The third moves sideways instead of up or down.
- Normal fault
- The hanging wall has moved down relative to the footwall. PHIVOLCS says normal faults happen where two blocks of rock are pulled apart by tension.
- Reverse fault
- The hanging wall has moved up relative to the footwall. PHIVOLCS says reverse faults happen where two blocks of rock are forced together by compression.
- Strike-slip fault
- The ground on either side moves sideways past the other, seen here from above. Standing on one side and looking across, if the far side has moved to your left it is left-lateral, and to your right it is right-lateral. The drawing shows right-lateral.
The dashed red line is the fault and the orange arrows show the movement. Drawn for this page from the PHIVOLCS definitions.
Source: PHIVOLCS, Earthquake Hazards. Read 23 October 2026.
PHIVOLCS uses the words hanging wall and footwall without defining them, so this is the site's own explanation: picture the fault as a slope running down into the ground. The block resting on top of it is the hanging wall, and the block underneath it is the footwall.
Two that moved here
These are the examples PHIVOLCS uses, with the places and dates it gives.
- Strike-slip: the Digdig segment of the Philippine Fault, in the magnitude 7.8 earthquake of 16 July 1990. The ground ruptured for 125 kilometers, from Dingalan, Aurora to Kayapa, Nueva Vizcaya, and rice paddies in Imugan, Nueva Vizcaya were displaced sideways to the left.
- Reverse: the North Bohol Fault, in the magnitude 7.2 Bohol earthquake of 15 October 2013. In Brgy. Anonang, Inabanga, the ground moved up by about 2 meters.
Source: PHIVOLCS, Earthquake Hazards. Read 23 October 2026.
Active or potentially active
PHIVOLCS sorts faults by how recently they moved. These are its two classes, closely paraphrased.
| Class | PHIVOLCS definition |
|---|---|
| Active fault | Moved within the last 10,000 years and will move again in the future. |
| Potentially active fault | Shows evidence of deformation, but whether it moved in the last 10,000 years is unclear. PHIVOLCS says future movement should not be discounted, and the fault can be reclassified as active when more information becomes available. |
The hazard that belongs to an active fault is ground rupture: the ground surface breaking and shifting along the fault. It is one of six hazards on the earthquake hazards page.
Source: PHIVOLCS, Earthquake Hazards. Read 23 October 2026.
How to find the active fault nearest you
PHIVOLCS's FaultFinder is a web tool that measures the shortest distance from a point to the nearest active fault, either from where your phone is or from a place you pick. These are the steps from the PHIVOLCS page.
- Step 1
Choose the fault system
In the Greater Metro Manila Area, click "Valley Fault System (VFS)" on the opening page. Anywhere else, click "Other Fault Systems".
- Step 2
Measure from where you are
Turn on your phone’s location, then click "VFS Fault Nearest You" or "Active Fault Nearest You".
- Step 3
Or measure from another place
Use the "Active Fault Based on Location" tab for a barangay, or "Double Click a Place on the Map" and double click the spot you want.
- Step 4
Read the result
It gives the distance to the nearest active fault, the fault and segment name, the year it was mapped and the map scale used.
PHIVOLCS adds that it keeps improving the fault information in the tool and advises the public to consult it directly for an official hazards assessment.
Source: PHIVOLCS, The PHIVOLCS FaultFinder. Read 23 October 2026.
HazardHunterPH, the GeoRiskPH tool, gives the distance to active faults and to volcanoes, and assesses more hazards than distance alone; how to use it is on the HazardHunterPH page.
This site gives no safe distance from a fault, because neither tool's page gives one.
Source: GeoRiskPH, DOST-PHIVOLCS, HazardHunterPH Frequently Asked Questions. Read 23 October 2026.
If a fault runs near you
What to do before the shaking, during it and after it is on these pages.
The earthquake guide The West Valley Fault Duck, cover and hold