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HAR Manual Logic Guide

A distilled logic reference for the PHIVOLCS Hazard Assessment Report (HAR) Engine.

🟢 Part 1: The Universal Boilerplate

Mandatory statements for every report, regardless of hazard status.

1. Introduction (Choose Source)

If your source is... Copy This:
Vicinity Map All hazard assessments are based on the latest available hazard maps and on the location indicated in the vicinity map provided.
Coordinates (GPS) All hazard assessments are based on the latest available hazard maps and on the location indicated by the coordinates provided.
No Map Provided All hazard assessments are based on the latest available hazard maps. In the absence of vicinity maps, the location of the property used were those indicated in Google Earth, Google Maps, or Wikimapia.

2. The "Supersedes" Clause (End of Report)

"This hazard assessment supersedes any previous assessment made by this office regarding the site."

🔵 Part 2: Earthquake Hazards Logic

Flow: Check Map → Select Status → Copy Explanation.

A. Active Fault (Ground Rupture)

Rule: ALWAYS explain, even if Safe.

Map Status Assessment Text Required Explanation / Recommendation
SAFE (> 5m away) Safe; Approximately [X] km [Direction] of the [Fault Name] Explanation: Ground rupture hazard assessment is the distance to the nearest known active fault.

Rec: The recommended buffer zone, or Zone of Avoidance, against ground rupture hazard is at least 5 meters on both sides of the active fault or from its zone of deformation.
PRONE (Buffer) Prone; Within the buffer zone Same as above.
PRONE (Transected) Prone; Transected by the [Fault Name] Same as above.

B. The "Silent if Safe" Hazards

Rule: If the map says SAFE, you write "Safe" and add no explanation. Only explain if PRONE.

Hazard If Map says PRONE, add this text:
EIL (Landslide) Expl: Earthquake-induced landslides are the downward slope movement of rocks, soil and other debris triggered by strong ground shaking.
Rec: Avoidance is recommended for sites with earthquake-induced landslide hazard unless appropriate engineering interventions are in place.
Tsunami Expl: A tsunami is a series of sea waves commonly generated by under-the-sea earthquakes and whose heights could be greater than 5 meters.
Rec: Tsunami threat to people's lives can be addressed by community preparedness and tsunami evacuation plan... (standard Tsunami evacuation text)

EIL — Standard Parameters (for General Elevation Profile / no regional data):

  • Slope Threshold: ≤ 15° (≤ 25%) → Safe. > 15° (> 25%) → Susceptible.
  • Depositional Zone: Safe if horizontal distance H > 3 × ΔE, where ΔE = Elev_Max − Elev_Min. If H ≤ 3 × ΔE, assess as: "Prone; Within the depositional zone."

Tsunami — No Map Data (Low-Lying Coastal Area): If the site is in a low-lying coastal area and no specific tsunami hazard map is available, use: "Low-lying coastal area is prone to local tsunami due to offshore fault or submarine landslide."

C. Liquefaction (The Exception)

Rule: Unlike EIL/Tsunami, Liquefaction has a mandatory recommendation even if Safe.

  • Assessment: Safe / Susceptible / Highly Susceptible
  • Mandatory Recommendation: "Ground shaking and liquefaction hazards can be mitigated by following the provisions of the National Building Code and the Structural Code of the Philippines."

GMMA-READY Maps — Special Formatting Rule: For GMMA-READY liquefaction maps, the output must be exactly "Low Potential", "Moderate Potential", or "High Potential". Never use the modifiers "partly" or "largely" for GMMA-READY maps, regardless of how much of the site falls within a given zone.

D. Ground Shaking (Universal)

  • Standard: "All sites may be affected by strong ground shaking."
  • Palawan/Sulu Only: Remove the word "strong".

🟠 Part 3: Volcano Hazards Logic

Follow this flowchart to avoid errors.

Step 1: The "50km Gatekeeper"

Measure distance to the nearest active volcano.

  • IF > 50 KM — or — outside the volcano watershed:

    1. Write: "Considering the distance of the site from the volcano, the site is safe from volcanic hazards such as pyroclastic density currents, lava flows, and ballistic projectiles that may originate from the volcano."
    2. Add Ashfall Statement (See Step 4).
    3. STOP. You are done. Do not assess Lahar/PDC/Lava.

    Island Volcano Exception: For sites outside a volcano island (e.g., Biliran, Hibok-Hibok), use instead: "Considering the distance of the site from the volcano, the site is safe from erupted products of a hazardous volcanic eruption."

  • IF < 50 KM — and — inside the volcano watershed:

    • Proceed to Step 1b, then Step 2.

Step 1b: AV vs. PAV Distance Conflict

Only applies when both an Active Volcano (AV) and a Potentially Active Volcano (PAV) are within 50 km.

Scenario Action
AV is nearer than PAV (both < 50 km) Assess the AV only.
PAV is nearer than AV (both < 50 km) Assess both the AV and PAV. Consult the Volcano Officer of the Day (VOOD).
Both AV and PAV are > 50 km away Assess the AV only.

Step 2: The PDZ Check (Permanent Danger Zone)

Does the site fall inside the circle?

Status Assessment Text Required Explanation
INSIDE PDZ The site is inside the [X]-kilometer Permanent Danger Zone... The Permanent Danger Zone (PDZ) is a zone that can always be affected by small-scale eruptions of [Volcano Name] Volcano. Human settlement is not recommended within the PDZ.
OUTSIDE PDZ The site is outside the [X]-kilometer Permanent Danger Zone... Same as above.

CRITICAL EXCEPTIONS:

  • Taal: PDZ is "Taal Volcano Island" (Not a radius).
  • Pinatubo: Uses "10-kilometer danger zone" (Not "PDZ").
  • Kanlaon/Bulusan/Hibok-Hibok: 4km radius.
  • Mayon: 6km radius.

Step 3: The "Silent if Safe" Volcano Hazards

Rule: Like Earthquake, generally only explain if PRONE.

Hazard If Map says PRONE, add this text:
Lahar Expl: Lahars are rapidly flowing mixtures of volcanic sediment and water...
Rec: Lahar threat to people's lives can be addressed by 1) observing or implementing legal easement... and 2) community preparedness...
PDC Expl: Pyroclastic Density Currents (PDCs)... are turbulent, fast-moving mixtures of volcanic fragments...
Rec: Avoidance is recommended for site/sites that may potentially be affected by PDCs and lava flows.
Lava Flow Expl: Lava flows are rivers of hot molten rock that can burn and bury land...
Rec: Use PDC recommendation above.
Ballistic Expl: Ballistic projectiles are fragments thrown at a close distance from the vent...
Volcanic Tsunami Expl: Volcanic tsunami can be generated by the sudden displacement of sea/lake water during volcanic eruption, flank collapse, or other volcanic processes. Volcanic tsunamis can cause inundation and washout of communities, drowning, physical injuries, and damage to infrastructure and properties.
Rec: Be aware of the three natural signs of tsunami: 1) strong ground shaking; 2) unusual rise or fall of lake/sea level; and 3) strong or unusual sound coming from the lake/sea. Evacuate immediately to higher ground upon observing any of these signs.

Step 4: Ashfall (Universal)

Rule: ALWAYS include this for Volcano reports, regardless of distance.

"In case of future eruptions of [Volcano Name] Volcano and other nearby volcanoes, the site/s may be affected by tephra fall/ ashfall depending on the height of the eruption plume and prevailing wind direction..."

🔴 Part 4: The "Red Flags" (Special Exceptions)

Check this list before finalizing any report.

1. TAAL VOLCANO

  • PDZ: Do not use kilometers. Use: "Taal Volcano Island is designated as the Permanent Danger Zone of the volcano."
  • Base Surge: If prone, explain: "Prone; Within the base surge buffer zone."
  • Fissures:
    • If Safe: "Safe; Approx [X] meters from mapped fissure."
    • Mandatory Note: "Stakeholders are advised to report to the Institute fissures that may be observed..."

1b. FISSURES — MUNTINLUPA

  • Fissure assessment is required for Muntinlupa sites that are less than 1 kilometer from the nearest mapped fissure.
  • Use the same Safe/Prone language and mandatory note as Taal fissures above.

2. PINATUBO

  • Lahar Zones: Do not use Prone/Safe. Use Zones (1-5).
    • Zone 1: High susceptibility to large-magnitude lahars.
    • Zone 4: Safe from lahars but susceptible to sediment-laden stream flows.
    • Zone 5: Safe from lahars but susceptible to flooding/backflooding.

3. MAYON

  • Lahar Categories:
    • Highly Prone: Adjacent to active river channels.
    • Moderately Prone: Medial/distal portions of lahar fans.
    • Least Prone: Distal portions or between river channels.

4. Potentially Active Volcanoes (PAV)

If the nearest volcano is a PAV (e.g., Mt. Arayat, Mt. Isarog).

  • Definition: "[Name] Volcano is currently classified... as a potentially active volcano... morphologically young-looking but with no historical or analytical records of eruption."
  • Lahar Warning: "The site is located on the alluvial fan near [Name] and may be potentially affected by lahars in the event of severe/prolonged precipitation..."