Figure 1 Seismotectonics of the two earthquakes affecting the province of Abra in northern Philippines in less than three months this year, namely a magnitude 7.0 July 27 and a magnitude 6.4 October 25. Result of Coulomb stress change modeling shown, using the July earthquake as source and the northeast striking, southeast dipping nodal plane of the focal mechanism solutions of the October earthquake as the receiver. Aftershocks of the two seismic events are shown as light purple circles with purple outline for the July earthquake, and light green circles with green outline for the October earthquake. Gray circles with white outline are background historical earthquake epicenters. Inset map on the lower right corner indicates place names of towns and provinces discussed in the text. Locations of CST cross sections A-A’, B-B’ and C-C’ shown in Figure 2 indicated as light green lines. References: Jarvis et al., 2008 for SRTM topography; Weatherall et al., 2020 for bathymetry; Toda et al., 2011 for CST modeling; PHIVOLCS for earthquake data. GMT (Wessel and Smith, 1995) was used to generate the map. See text for more discussion. Credit: Aurelio, Catugas, Ramirez, Aurelio, Lagmay.

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Figure 1 Seismotectonics of the two earthquakes affecting the province of Abra in northern Philippines in less than three months this year, namely a magnitude 7.0 July 27 and a magnitude 6.4 October 25. Result of Coulomb stress change modeling shown, using the July earthquake as source and the northeast striking, southeast dipping nodal plane of the focal mechanism solutions of the October earthquake as the receiver. Aftershocks of the two seismic events are shown as light purple circles with purple outline for the July earthquake, and light green circles with green outline for the October earthquake. Gray circles with white outline are background historical earthquake epicenters. Inset map on the lower right corner indicates place names of towns and provinces discussed in the text. Locations of CST cross sections A-A’, B-B’ and C-C’ shown in Figure 2 indicated as light green lines. References: Jarvis et al., 2008 for SRTM topography; Weatherall et al., 2020 for bathymetry; Toda et al., 2011 for CST modeling; PHIVOLCS for earthquake data. GMT (Wessel and Smith, 1995) was used to generate the map. See text for more discussion. Credit: Aurelio, Catugas, Ramirez, Aurelio, Lagmay.

Figure 1 Seismotectonics of the two earthquakes affecting the province of Abra in northern Philippines in less than three months this year, namely a magnitude 7.0 July 27 and a magnitude 6.4 October 25. Result of Coulomb stress change modeling shown, using the July earthquake as source and the northeast striking, southeast dipping nodal plane of the focal mechanism solutions of the October earthquake as the receiver. Aftershocks of the two seismic events are shown as light purple circles with purple outline for the July earthquake, and light green circles with green outline for the October earthquake. Gray circles with white outline are background historical earthquake epicenters. Inset map on the lower right corner indicates place names of towns and provinces discussed in the text. Locations of CST cross sections A-A’, B-B’ and C-C’ shown in Figure 2 indicated as light green lines. References: Jarvis et al., 2008 for SRTM topography; Weatherall et al., 2020 for bathymetry; Toda et al., 2011 for CST modeling; PHIVOLCS for earthquake data. GMT (Wessel and Smith, 1995) was used to generate the map. See text for more discussion. Credit: Aurelio, Catugas, Ramirez, Aurelio, Lagmay.

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