Question now is, what sort of thing can happen in the red patch area?
WHAT SILENT DANGER LURKS
Note: the road that is a yellow line cutting through the red patch is MARCOS HIGHWAY; while the yellow line traversing the pink and then goes between the pink and red areas is SUMULONG HIGHWAY. Where these two lines intersect is Masinag. Notice also the faint bright green lines that are sort of “secret” fault lines that Phivolcs is not telling? These may well explain the unexplained danger the “red patch” hides.
Can it be in the red patch area are the slopes of mountainside that will further drop when compromised land mass breaks off at its junction to these faults, as triggered by a 7.2 magnitude quake? Notice the “scooped” stretch along Marcos Highway, where an ocular visit to the area reveals rising hills and mountains on one side while the other side is likewise rising with access roads to Sumulong Highway via Blue Mountain and Olalia Drive on Gate 2. It is the same rise in elevation that can be observed when driving along Sumulong Highway from Brgy. Mambugan to Valley Golf Subdivision and onward to St. Benilde College and so on.
The “valley” aspect (ground depression) when the east and west valley faults formed never quite followed suit along the stretch of Marcos Highway where the ground rises on its sides as mountain slopes. But the next predicted powerful earthquake may just turn the shallow scoop into a deep valley when the same land mass drops further by several tens of feet!
How big is the drop? If it is any indication, the disparity in the ground elevation of Katipunan Ave. in Quezon City and the Industial Valley Subdivision in Marikina, where these two are connected by a looping short road called Bitukang Manok, or the back of Ateneo University which is actually a ravine for the lowland Brgy. Barangka in Marikina below it, a vertical ground movement on the tell-tale red patch in Antipolo may just imitate this valley effect.
Though it is not a sink hole, but by another mechanism it can likewise have a disastrous effect with mass landslides triggered.
Videos, anyone? (you have to download them first.)
My recordings of Antipolo and the surrounding mountainsides as simulated (fairly) in the 3D environment of Google Earth.