Figure 1. Seismotectonic map of the earthquake swarms. We show the locations of the 2023 magnitude 6.8, 2002 magnitude 6.8, 1976 magnitude 8.1, and 1918 magnitude 8.3 earthquakes. The aftershock area related to the 1976 magnitude 8.1 Moro Gulf Earthquake (Badillo and Astilla, 1978) is also plotted in this map as a dashed gray ellipse. The blue dashed line projects the location of the cross-section in Figure 3. Solid lines projected on the focal mechanism solutions or beachballs (red line for the 2023 magnitude 6.8 earthquake; gray line for the 2025 Palimbang earthquake swarm; and yellow line for the 2026 Kalamansig earthquake swarm) emphasize the trend of the east-dipping fault planes. Data sources: Earthquake locations from DOST-PHIVOLCS and ISCGEM, focal mechanisms from DOST-PHIVOLCS SWIFT-CMT catalog (Bonita et al., 2025), location of active faults, potentially active faults, and trenches from DOST-PHIVOLCS, SAR-derived topography and bathymetry from NAMRIA. Credit: Llamas et al., 2026, CC BY-NC-ND 4.0

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Figure 1. Seismotectonic map of the earthquake swarms. We show the locations of the 2023 magnitude 6.8, 2002 magnitude 6.8, 1976 magnitude 8.1, and 1918 magnitude 8.3 earthquakes. The aftershock area related to the 1976 magnitude 8.1 Moro Gulf Earthquake (Badillo and Astilla, 1978) is also plotted in this map as a dashed gray ellipse. The blue dashed line projects the location of the cross-section in Figure 3. Solid lines projected on the focal mechanism solutions or beachballs (red line for the 2023 magnitude 6.8 earthquake; gray line for the 2025 Palimbang earthquake swarm; and yellow line for the 2026 Kalamansig earthquake swarm) emphasize the trend of the east-dipping fault planes. Data sources: Earthquake locations from DOST-PHIVOLCS and ISCGEM, focal mechanisms from DOST-PHIVOLCS SWIFT-CMT catalog (Bonita et al., 2025), location of active faults, potentially active faults, and trenches from DOST-PHIVOLCS, SAR-derived topography and bathymetry from NAMRIA. Credit: Llamas et al., 2026, CC BY-NC-ND 4.0

Figure 1. Seismotectonic map of the earthquake swarms. We show the locations of the 2023 magnitude 6.8, 2002 magnitude 6.8, 1976 magnitude 8.1, and 1918 magnitude 8.3 earthquakes. The aftershock area related to the 1976 magnitude 8.1 Moro Gulf Earthquake (Badillo and Astilla, 1978) is also plotted in this map as a dashed gray ellipse. The blue dashed line projects the location of the cross-section in Figure 3. Solid lines projected on the focal mechanism solutions or beachballs (red line for the 2023 magnitude 6.8 earthquake; gray line for the 2025 Palimbang earthquake swarm; and yellow line for the 2026 Kalamansig earthquake swarm) emphasize the trend of the east-dipping fault planes. Data sources: Earthquake locations from DOST-PHIVOLCS and ISCGEM, focal mechanisms from DOST-PHIVOLCS SWIFT-CMT catalog (Bonita et al., 2025), location of active faults, potentially active faults, and trenches from DOST-PHIVOLCS, SAR-derived topography and bathymetry from NAMRIA. Credit: Llamas et al., 2026, CC BY-NC-ND 4.0

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