The Joel Espanol Maturan Blog: When the Ground Moves: Earthquakes, the Philippine Fault System, and Preparing for “The Big One"

When the Ground Moves: Earthquakes, the Philippine Fault System, and Preparing for “The Big One"

Earthquakes are part of life in the Philippines — a nation sitting squarely on the Pacific “Ring of Fire.” Recent events (notably the 2013 Bohol quake and the deadly 2025 Cebu quake) remind us that seismic risk is real and persistent. This blogpost explains the Philippine fault system in plain language, compares the Bohol and Cebu events, summarizes what scientists say about the chance of a future major quake (including the oft-discussed “Big One” for Metro Manila), and — most importantly — gives practical, barangay- and household-level preparedness steps you can start now.

Quick overview: why earthquakes happen here

The Philippine archipelago lies where several tectonic plates interact. Large active faults and subduction zones produce the majority of the country’s earthquakes. Some faults (like the North Bohol Fault that ruptured in 2013) produce powerful shallow temblors that cause severe local damage. Other systems — such as the Valley Fault System (including the West Valley Fault) near Metro Manila — pose catastrophic risk because they run beneath densely populated areas. PHIVOLCS maintains active-fault maps and monitoring for these hazards. PHIVOLCS+1

The Bohol quake (Oct 15, 2013) and the recent Cebu quake (Sept 30, 2025) — dates and coincidence

Bohol earthquake: a magnitude ~7.2 event struck on 15 October 2013, with epicenter in Bohol. It produced extensive ground rupture, damaged many heritage churches and buildings, and caused hundreds of deaths and thousands displaced.
Cebu earthquake (2025): a shallow magnitude ~6.9 quake struck northern Cebu on 30 September 2025, causing major damage in Bogo City and surrounding towns and was described in news reports as the deadliest earthquake in the Philippines since 2013. Reuters+1

Note on “coincidence”: what links the two events is geographic and temporal context — both struck the central Visayas region and both produced shallow, damaging shaking. They did not occur on the same calendar date; the 2013 event was Oct 15, 2013, while the Cebu event was Sept 30, 2025. The 2025 quake is often described in media as the most lethal since the 2013 Bohol quake. PHIVOLCS+1

What scientists say about when a quake will happen (and what they don’t say)

You cannot predict the exact day or hour. Agencies like PHIVOLCS issue models, scenario studies and maps of active faults and likely shaking intensities, but they do not give precise dates for earthquakes — only probabilistic assessments and recurrence information.
The West Valley Fault (“The Big One”) scenario. PHIVOLCS and related studies identify the West Valley Fault (WVF) as one of the highest-impact sources for Metro Manila: models and scenario studies commonly show a potential ~M7–7.2 event that could produce Intensity VIII shaking near the fault, extensive building damage, liquefaction and ground rupture. Studies that feed into building-code hazard maps use probabilistic seismic hazard analysis (PSHA) to estimate ground motions for return periods (e.g., 50-year, 475-year, 2475-year) — these are probabilities of exceedance, not schedules. Media coverage and PHIVOLCS scenario work have warned that a major WVF event could result in tens of thousands of casualties and widespread infrastructure collapse if no mitigation is done. ISSMGE+1

Bottom line for “when”: experts can and do estimate the likelihood and potential impacts of a major quake in a region (and they map which areas are most vulnerable), but they cannot say when on a day/month/year scale the quake will happen. Preparation must therefore be ongoing.

Reading the technical signals — what data researchers use

Seismologists and hazard modelers combine:

active-fault mapping (surface traces, length and slip rates),
paleoseismology (past earthquakes and recurrence intervals — e.g., WVF has moved several times in the last 1,400 years; recurrence estimates inform “overdue” discussions),
instrumental seismicity (recent earthquakes), and
probabilistic seismic hazard analysis (PSHA) to estimate the ground motions likely in a given time window.
These inputs drive scenario planning (e.g., ground-shaking maps, collapse estimates) used by planners and engineers. But again: probabilistic — not deterministic. PHIVOLCS+1

Simple, practical analysis: how to assess your risk now

Find the nearest active fault — PHIVOLCS has fault maps and the FaultFinder tool to check if your barangay sits near an active trace. If your house is within the hazard zone of a mapped fault, prioritize relocation or structural mitigation. PHIVOLCS
Soil matters — soft reclaimed or alluvial soils amplify shaking and are prone to liquefaction. If you live on low-lying reclaimed ground (many metro coastal areas), expect stronger shaking and higher damage risk. Hazard maps and local government unit (LGU) land-use plans should show these zones. ISSMGE
Building vulnerability — unreinforced masonry and non-engineered structures fail more readily. If your barangay has many old or informal houses, plan phased retrofits and a contingency plan for rapid evacuations. GMA Network

Preventive measures — what barangays, LGUs, and families should do (actionable steps)

For barangay and LGU level

Map hazards & safe zones. Use PHIVOLCS maps and local surveys to tag high-risk areas (fault traces, liquefaction zones, landslide-prone slopes) and identify evacuation routes, muster points, and temporary shelter locations. PHIVOLCS
Enforce land-use and building codes. Do not allow new critical structures on mapped fault traces or high-liquefaction sites; implement stricter codes for hospitals, schools, evacuation centers, and government buildings. ISSMGE
Community retrofitting programs. Provide subsidies, training or micro-grants to help homeowners reinforce roofs, walls, anchor heavy items, and retrofit foundations. Prioritize schools, clinics, and evacuation centers. GMA Network
Early-warning and communication systems. While we don’t have long-term earthquake warnings, rapid earthquake alert systems and robust local communications (SMS trees, radio, barangay PA systems) save lives in the seconds–minutes immediately after shaking starts. PHIVOLCS
Drills and coordination. Regular barangay-wide drills (evacuation, search-and-rescue basics, first aid) and an agreed emergency inventory (food, water, medicines, tarpaulins) are crucial.

For households and individuals

Emergency kit (grab-and-go): water (3–5 liters per person/day for 3 days), nonperishable food, flashlight and extra batteries, first-aid kit, medications, copies of IDs/important documents (digital + print), cash, face masks, basic tools, whistle, portable phone charger.
Home hazard-proofing: bolt bookcases and cabinets to studs; secure heavy appliances and water heaters; place heavy items on low shelves; anchor the water heater; fit latches on cabinets; locate safe spots in each room (door frames are not always safe — identify sturdy table to “Drop, Cover, Hold On”).
Family emergency plan: agreed meeting point outside the house; emergency contact list (local barangay DRR officer, relatives); designate who will turn off utilities if safe (gas, electricity); plan for pets.
Education & drills: practice “Drop, Cover, Hold On” with family and children; teach how to turn off gas and water; know your barangay’s evacuation routes.

What to do during a quake

If indoors: Drop, Cover, and Hold On — get under sturdy furniture, protect your head, stay away from windows, exterior walls and heavy furniture that can topple. Do not run outside during shaking (falling debris is the main hazard).
If outdoors: Move away from buildings, walls, trees, streetlights, and utility wires. Find an open area.
If driving: Pull over safely, stop, and stay inside the vehicle until shaking stops; avoid bridges and overpasses if possible.

(These are standard lifesaving actions promoted by seismological agencies and disaster authorities.) PHIVOLCS

Recovery and long-term resilience (what to invest in now)

Infrastructure resilience: upgrade hospitals, water networks, lifelines and transportation links to withstand shaking and to enable faster recovery. Urban planning should avoid critical infrastructure on fault traces and liquefaction-prone land. ISSMGE
Economic preparedness: establish barangay-level contingency funds, pre-arranged supplier lists for emergency materials, and clear protocols to quickly assess building safety after quakes so neighborhoods can return to normal faster.
Public information & culture of readiness: continuous public education reduces fatalities and speeds recovery — people who know what to do are more likely to survive and help others.

Final assessment: how likely is the next big quake?

Short answer: we cannot predict when. Scientists provide probabilities and scenarios that show a real risk of large events on known faults (including the WVF scenario for Metro Manila). The existence of mapped faults, recurrence intervals, and recent seismicity (like the 2013 Bohol and 2025 Cebu events) means preparedness must remain a top priority. Use PHIVOLCS resources and LGU hazard maps to determine local risk and act accordingly. PHIVOLCS+1

Resources & references (key sources used)

PHIVOLCS — 2013 Bohol earthquake summary and active-fault maps. PHIVOLCS+1
Reuters reporting on the 2025 Cebu earthquake and impacts. Reuters
TIME coverage of the 2025 Cebu quake (context and aftermath). TIME
Technical hazard modeling and Metro Manila PSHA studies (West Valley Fault hazard and scenario assessments). ISSMGE
Recent PHIVOLCS and national press coverage summarizing the “Big One” scenario and guidance. GMA Network+1

Closing: what you can do this week

Locate PHIVOLCS hazard map for your barangay (use FaultFinder) and mark whether your home lies near a mapped fault. PHIVOLCS
Assemble a basic emergency kit (water, food, first-aid, flashlight, cash).
Run a 5-minute family drill: identify safe spots, practice Drop–Cover–Hold, decide on meeting point.
Talk to your barangay captain about community retrofitting priorities and the barangay DRRM plan.