The Vigan-Aggao Fault is a 140-km-long complex active fault system consisting of multiple traces in the westernmost part of the Philippine Fault Zone (PFZ) in northern Luzon, the Philippines. In this paper, its traces, segmentation, and oblique left-lateral strike-slip motion are determined from horizontal and vertical displacements measured from over a thousand piercing points pricked from displaced spurs and streams observed from Google Earth Pro satellite images. This work marks the first instance of the extensive use of Google Earth as a tool in mapping and determining the kinematics of active faults. Complete 3D image coverage of a major thoroughgoing active fault system is freely and easily accessible on the Google Earth Pro platform. It provides a great advantage to researchers collecting morphotectonic displacement data, especially where access to aerial photos covering the entire fault system is next to impossible. This tool has not been applied in the past due to apprehensions on the positional measurement accuracy (mainly of the vertical component). The new method outlined in this paper demonstrates the applicability of this tool in the detailed mapping of active fault traces through a neotectonic analysis of fault-zone features. From the sense of motion of the active faults in northern Luzon and of the major bounding faults in central Luzon, the nature of deformation in these regions can be inferred. An understanding of the kinematics is critical in appreciating the distribution and the preferred mode of accommodation of deformation by faulting in central and northern Luzon resulting from oblique convergence of the Sunda Plate and the Philippine Sea Plate. The location, extent, segmentation patterns, and sense of motion of active faults are critical in coming up with reasonable estimates of the hazards involved and identifying areas prone to these hazards. The magnitude of earthquakes is also partly dependent on the type and nature of fault movement. With a proper evaluation of these parameters, earthquake hazards and their effects in different tectonic settings worldwide can be estimated more accurately.

A 75 km-long, generally NE-striking ground rupture associated with the 6 February 2012 M_W 6.7 (M_b 6.9) Negros earthquake was mapped on the eastern side of Negros Island, Philippines. It closely follows a previously unmapped, pre-existing fault trace along the coast which is marked mostly by terrace-forming scarps. The dominance of vertical separation (west side up) is consistent with a west-dipping reverse fault, as indicated by focal mechanism solutions. The ground rupture map eliminates the ambiguity in the focal mechanism solution regarding the orientation, sense of motion, and location of the seismogenic fault plane, which are indispensable in the assessment of seismic hazards and the nature and distribution of deformation. This study uses the ground rupture map of the 2012 Negros earthquake in sorting out the mechanism of deformation in the Visayas Islands region. The ground rupture’s length is well within the aftershock area while its scarp heights are consistent with an earthquake of its magnitude and nature of movement. The 2012 Negros earthquake rupture’s pattern, scarp types, and offset of man-made structures are similar to those of recent reverse/thrust ground ruptures mapped globally and are distinct from those associated with erosion, landslide, and liquefaction. The onshore coseismic reverse fault of the Negros earthquake, which contradicts a model of coseismic slip on an offshore blind thrust fault by previous workers, represents the first thoroughly mapped ground rupture of its kind in the Philippines. The ground ruptures of the 2012 Negros and 2013 Bohol earthquakes, along with the Philippine Trench and the Philippine Fault Zone (PFZ), represent a complex shear partitioning mechanism in the Visayas Islands region. This departs from the current simple shear partitioning model for the region and is distinct from those for other regions along the PFZ and adjacent subduction zones. This study shows how an appreciation of morphotectonic features can lead to a better understanding of the distribution of deformation and the nature of earthquake hazards.

Accelerated creep, primarily through vertical displacement, has been occurring along 15 en-echelon faults belonging to a 15 km-long and 1.5 km-wide, N-S-trending dilational jog of the active West Valley Fault (or West Marikina Valley Fault), on the southeastern part of Metro Manila, Philippines. The much-larger-than-known tectonic slip rates had been the only reliable evidence in support of excessive groundwater withdrawal as the trigger of creep in the 1990s. Recently available groundwater extraction data (1977–2019) could more directly and consistently link groundwater withdrawal to accelerated creep in the 1990s. Twenty years (1999–2019) of precise displacement measurements could also reveal significant spatial and temporal links between slip rate changes and patterns of groundwater extraction. Our analysis shows that greater rates of vertical displacement are related to the timing of faster extraction rates. Variations in slip rates between the northern and southern measurement sites are primarily due to regional differences in groundwater extraction, which are influenced by differences in the implementation of water extraction reduction regulations. Proximity to the key source of groundwater recharge (Laguna Lake) is also an influencing factor. Although there are many unknowns inherent to this type of study, continued depressurization could induce static stress changes that could modulate the timescale of earthquake occurrence due to the natural course of stress loading driven by regional tectonics. The current and potential effects of continued depressurization in the areas with high slip rates and surrounding regions are paramount considerations in crafting and implementing tighter and extended groundwater extraction regulations.

Contemporary reverse faults, marked by offset boreholes, were identified in two roadcuts, and recently formed pop-ups, which are surficial chevron folds, have been recognized in a quarry in the Ottawa-Hull area of Ontario and Quebec, Canada. Displacement directions of the hanging walls, marked by the offset boreholes, are commonly north-northeast to east-northeast, though one set shows displacement to the northwest. The pop-ups recorded during this investigation show average orientations of 120 and 063°. These are similar to the average trends of 136 and 074° documented in a previous study from a quarry about 20 km away. East-southeast- to southeast-trending pop-ups predominate in the two quarries and are kinematically compatible with most of the offset borehole directions recognized to date in the Ottawa-Hull area. Moreover, the quarry-floor pop-up trends in the Ottawa-Hull area are consistent with those of open field, lake bottom and other quarry-floor pop-ups in an area extending from the Miramichi region of New Brunswick into the east-central U.S.A. The compressional origin of the reverse faults and pop-ups, and the predominant orientations of those structures, are compatible with the current ambient stress field in eastern North America. This implies that both the displaced boreholes and quarry-floor pop-ups are products of that stress field, and, despite their presence in excavations, are tectonic in origin.