Steven Cahill of Guam Homeland Security told the Mayor’s Council of Guam that existing village inundation maps are available on the GHS website but are based on an aggressive NOAA/PMEL study; GHS is working with the University of Hawai‘i to produce updated tsunami modeling.

Cahill said the current public products were computed from a high-end scenario and that geologists consider about 8.3 the upper-bound magnitude for events from the Marianas Trench. He summarized modeling outputs saying an 8.3 event could produce roughly a 9.5-foot surge arriving at roughly 12.2 knots, and emphasized the urgency for residents near coasts to evacuate immediately when they feel strong shaking.

"Feeling a strong earthquake... people need to immediately get away from the coastal areas," Cahill said, adding that local events from the Marianas Trench can arrive within about 10 minutes — a time frame too short for some external bulletin systems to respond — so recognizing natural warning signs is essential.

Cahill showed the council where to find village evacuation and assembly-area maps on the GHS website and said maps for southern villages have been updated; FY25 work will expand modeling to Tumon and Hagatna Bay. He also told mayors that some fixed sirens remain to be installed in Pago Bay and several other locations and thanked mayors for participating in AHAS monthly testing.

Cahill noted the National Tsunami Hazard Mitigation Program (NTHMP) — funded historically through NOAA — has seen cuts at the congressional level, leaving the program to “do more with what we got,” he said. Mayors raised questions about river inundation and whether village maps capture inland flow; Cahill confirmed the maps include inundation extents for rivers in affected villages and demonstrated the website’s zoom and satellite functions.

No formal action was taken; mayors were urged to review village evacuation maps, discuss vertical-evacuation and assembly-area locations with constituents, and report siren/audibility test results through the emergency group chat.