At 00:43 UTC on 27 July 2022, a 15-km deep major earthquake with magnitude (M_w) 7.0 struck Northwestern Luzon, Philippines. The strongest ground shaking felt was at PHIVOLCS Earthquake Intensity Scale (PEIS) VII (destructive), equivalent to Modified Mercalli Intensity (MMI) VII, in Abra and along the coastal areas of Ilocos Sur. More than a thousand landslides, rockfalls and tension cracks were mapped, near the epicentral region, in the northwestern part of the Central Cordillera. Most of the landslides were shallow-seated, many of which were situated along road cuts. Liquefaction manifested as lateral spreads, sand boils, fissures, ground subsidence, and localized swelling was documented along the coastal areas of Ilocos Sur and river channels in Abra and Ilocos Sur. Sea level disturbance was also observed in some coastal areas of Ilocos Sur and La Union. Damages to buildings and infrastructures were documented in areas that experienced PEIS VI (very strong), equivalent to MMI VI and PEIS VII (destructive). Earthquake data, including hypocentral location, aftershock distribution, focal mechanism solutions and strong motion data, and InSAR observation indicate that the earthquake was generated by an almost north-south striking reverse left-lateral oblique fault that is gently dipping to the east. There is no clear indication of a surface rupture based on InSAR analysis and field investigation. The spatial distribution of geologic impacts, such as earthquake-induced landslides and liquefaction, is strongly controlled by the causative fault, the direction of rupture propagation and geology. Peak ground acceleration (PGA) records show a unidirectional rupture propagation and are congruent with the spatial distribution of earthquake impacts. Although earthquake parameters, deformation analysis and field data suggest that the Abra River Fault is the probable causative fault, the derived geometry and kinematics from the seismotectonic analysis challenge our existing understanding of the nature of the Abra River Fault, as well as the other segments of the Philippine Fault. The need to understand these earthquake sources in the country is needed for a better seismic hazard and risk assessment.

In the period of October–December 2019, the Cotabato–Davao del Sur region (Philippines) was hit by a seismic sequence comprising four earthquakes with magnitude M_W > 6.0 (EQ1-4; max magnitude M_W 6.8). The earthquakes triggered widespread environmental effects, including landslides and liquefaction features. We documented such effects by means of field surveys, which we supplemented with landslide mapping from satellite images. Field surveys allowed us to gather information on 43 points after EQ1, 202 points after EQs2–3 and 87 points after EQ4. Additionally, we built a multi-temporal inventory of landslides from remote sensing, comprising 190 slope movements triggered by EQ1, 4737 after EQs2–3, and 5666 at the end of the sequence. We assigned an intensity value to each environmental effect using the environmental seismic intensity (ESI-07) scale. Our preferred estimates of ESI-07 epicentral intensity are VIII for the first earthquake and IX at the end of the sequence, which is in broad agreement with other events of similar magnitude globally. This study, which is the first case of the application of the ESI-07 scale to a seismic sequence in the Philippines, shows that repeated documentation of environmental damage and the evaluation of the progression through time may be useful for providing input data for derivative products, such as susceptibility assessment, evaluation of residual risk or investigation of the role played by ground shaking and by other mechanisms able to trigger environmental effects.

On 15 January 2023, a shallow, moderate earthquake with a magnitude (M_w) of 4.7 and a depth of one kilometer struck the northern part of Leyte Island in the central Philippines. Originating along the northern Leyte segment of the Philippine Fault, a well-established creeping fault, the earthquake caused significant geologic, structural, and socio-economic impacts despite its low magnitude. Probable surface rupture and landslides were reported, leading to a comprehensive field investigation. Our investigation revealed an ~8 km discontinuous surface rupture along the northern Leyte segment of the Philippine Fault, with a maximum left-lateral displacement of 2 cm. This was the first documented occurrence of such a phenomenon associated with an earthquake of a magnitude less than 6, particularly along a creeping fault segment. The maximum ground shaking felt was reported on the PHIVOLCS Earthquake Intensity Scale (PEIS) to be VI (very strong), equivalent to a Modified Mercalli Intensity (MMI) of VI along the fault strike. However, strong motion accelerographs recorded a peak ground acceleration (PGA) of 0.407 g, equivalent to PEIS VIII (very destructive), attributed to local site amplification influenced by subsurface geology. In the area where the local site amplification occurred, limited liquefaction was observed on marshlands with recent and alluvial deposits. Two landslides were observed in the mountainous area west of the fault. Structural damages were noted in areas with PEIS VI intensity and areas transected by the surface rupture. Despite the earthquake’s low magnitude, the event documented significant impacts, including surface ruptures, liquefaction, landslides, and severe structural damage. The peculiarities of this event are attributed to the shallowness of the earthquake source, and local site conditions, including geology, geomorphology, and soil properties, contributed to the severity of the impacts. Moderate in size, this earthquake emphasizes the importance of documenting moderate-sized earthquakes as a tool and guide for medium- and long-term earthquake risk assessment and resiliency.