🇨🇴🌎 ANALYSIS — Why Monday's M7.4 Colombia earthquake was felt across multiple countries but didn't flatten a single town.
The key is depth. Per the USGS, the quake struck ~107 km down (Colombia's SGC says 96 km) — an intermediate-depth event caused by strike-slip faulting within the subducting Nazca plate, not a shallow rupture at the surface. The Nazca plate is dense oceanic crust grinding eastward and sinking beneath the South American (North Andes) plate — the same process that built the Andes.
At ~100 km down, the thick rock above acted as a buffer for the high-frequency waves that destroy houses, while transmitting low-frequency waves that travel far. Instead of concentrating energy on one town, the shaking spread hundreds of kilometers — which is why it was felt across Colombia, Ecuador, and Panama. (Reports of it being felt in Venezuela are circulating but not confirmed; the epicenter sits in Colombia's far west, near the Pacific.)
Why Cali was hit harder than its distance suggests: much of the city sits on soft sediment in the Cauca Valley, which amplifies and prolongs seismic waves through resonance — the same soil-amplification effect that made Mexico City so vulnerable in 1985. Older unreinforced brick and non-confined structures are most at risk under that prolonged shaking, and Cali is now reporting structural collapses and trapped persons. (No deaths confirmed as of now — "lethal" framing is premature.)
The USGS estimates a ~77 km rupture and energy near 1.9 megatons of TNT. No tsunami threat, precisely because it was so deep.
Sources: USGS, Servicio Geológico Colombiano, PTWC, The Watchers
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