The Philippines records about 20 earthquakes a day, and most are too small to feel. Each one is still detected, located and logged. This guide follows a quake from the first tremor to the dot that appears on a map. It also explains how to read the numbers, and why they sometimes change.
The Philippine Seismic Network
The backbone of earthquake monitoring is the Philippine Seismic Network (PSN), operated by PHIVOLCS under the Department of Science and Technology. It has grown steadily. There were 64 stations in 2010 and more than 90 by 2016. Recent reports put the total at about 128–129 stations, spread from Batanes to Tawi-Tawi.
Seismic stations
Seismometers that record ground motion around the clock. Some are staffed observatories and others run unmanned.
Intensity meters
Instruments that measure how strongly the ground actually shakes at a site, using the PHIVOLCS intensity scale.
Volcano networks
Dedicated stations around active volcanoes such as Taal, Mayon and Kanlaon that track volcanic earthquakes.
All station data flows to the Data Receiving Center at the PHIVOLCS main office in Diliman, Quezon City, which is staffed 24 hours a day. PHIVOLCS has also opened regional cluster monitoring centers, starting with one in San Fernando, Cebu for the Visayas, so monitoring doesn't depend on a single site.
From first tremor to bulletin: what happens
- Waves spread out. When a fault slips, it sends out fast P-waves (primary waves) followed by slower, stronger S-waves (secondary waves).
- Stations record them. Seismometers closest to the epicenter pick up the waves first, then stations farther away do. The data is sent to Quezon City in near real time.
- The quake is located. Comparing when the waves reached at least three stations pins down the epicenter (the point on the surface) and the depth.
- Magnitude is estimated. The size of the recorded waves, adjusted for distance, gives the magnitude, a single number for the energy released.
- A preliminary bulletin goes out. An automatic solution is typically published about 5–10 minutes after the quake.
- Analysts review it. Seismologists check the solution, add felt and instrumental intensity reports, and issue updated bulletins. Magnitude and location may change slightly.
Why the first numbers sometimes change
The automatic solution relies on the first few stations to report. As more data comes in, the estimate gets better. A quake first reported as magnitude 5.9 might be revised to 6.1, or its epicenter may shift a few kilometers. Revisions are normal and show the system improving its estimate.
Magnitude vs. intensity: two different measurements
A bulletin contains two kinds of numbers, and they measure different things:
- Magnitude (for example 6.2) is the quake's size at its source. There is one value per earthquake.
- Intensity (for example Intensity V) is how strongly shaking was felt in a particular place. It is reported in Roman numerals from I to X on the PHIVOLCS Earthquake Intensity Scale (PEIS), and it differs from town to town.
Intensity comes from two sources. Instrumental intensity is recorded by intensity meters. Reported intensity comes from local officials and the public describing what they felt and saw. For a deeper look, see our guide to magnitude vs. intensity.
Why PHIVOLCS and USGS numbers can differ
Large Philippine quakes are also measured by international agencies such as the U.S. Geological Survey (USGS). Their figures often don't match exactly:
| PHIVOLCS | USGS | |
|---|---|---|
| Stations used | Dense local network inside the Philippines | Global network, with fewer stations close to the quake |
| Small quakes | Detects and reports many below magnitude 3 | Mostly catalogs around magnitude 4–4.5 and up in this region |
| Local intensity | Official PEIS intensities and felt reports | "Did You Feel It?" estimates (a different scale) |
| Official advisories | Yes: the mandated source for the Philippines | No: for information only |
Differences of a few tenths of a magnitude and a few kilometers in location are common, especially in early reports. Neither agency is "wrong." They use different data and methods. For anything affecting safety in the Philippines, such as tsunami warnings, evacuations or school suspensions, follow PHIVOLCS.
Tsunami monitoring
When a strong, shallow quake strikes offshore, PHIVOLCS assesses whether it could generate a tsunami and issues tsunami information or warnings for affected coastlines. It does this alongside regional warning centers in the Pacific. Mobile networks can push these alerts to phones as emergency cell broadcasts. But for a local tsunami, the waves can arrive before any message does. Strong shaking near the coast is your warning: move to high ground right away.
What monitoring can't do
No one can predict earthquakes
Seismic networks detect earthquakes after they begin. No agency in the world can predict the exact time, place and size of a future quake. Messages claiming "a magnitude 8 will hit Manila on Friday" are always fake. What monitoring does provide is long-term hazard mapping of active faults, aftershock forecasts and rapid tsunami assessment.
How you can follow seismic activity
- PHIVOLCS: official bulletins, tsunami advisories and the PEIS guide.
- HazardHunterPH: check the earthquake, volcano and flood hazards at any address. See our guide on checking if your house is near a fault line.
- Earthquakes PH live map: recent quakes across the Philippines on one map, with magnitude, depth, active faults and daily activity.
- Report what you felt. PHIVOLCS uses public felt reports to map intensity, so your report helps.
Track live seismic activity across the Philippines and check what's near you.
Frequently asked questions
How does PHIVOLCS detect earthquakes?
Through the Philippine Seismic Network, roughly 130 stations whose seismometers send data in near real time to a 24/7 center in Quezon City. There, the arrival times at several stations are used to calculate the epicenter, depth and magnitude.
How fast does PHIVOLCS report an earthquake?
The automatic preliminary bulletin usually comes out within about 5 to 10 minutes. A reviewed bulletin follows, and may include small revisions.
Why do PHIVOLCS and USGS report different magnitudes?
They use different stations, methods and sometimes different magnitude types. Small differences are normal. In the Philippines, PHIVOLCS is the official source.
Can PHIVOLCS predict earthquakes?
No. No agency can predict earthquakes. Monitoring detects quakes as they happen and supports warnings and hazard planning.
How do I report an earthquake I felt?
Use the PHIVOLCS Earthquake Intensity Scale to judge what you experienced, then report it through PHIVOLCS's official channels.
Related: why the Philippines has so many earthquakes, aftershocks explained, and the earthquake safety guide.
Sources: PHIVOLCS (seismic monitoring network, earthquake monitoring system, earthquake information bulletins, PEIS); DOST news releases on the Visayas cluster monitoring center; USGS Earthquake Hazards Program. Station counts change as the network expands under the PHIVOLCS Modernization Act (RA 12180, 2025).