AS an engineer who advises companies on how to make their buildings survive earthquakes, I have visited the aftermath of nearly every key quake since 1970, observing how new and old buildings have performed when the ground shook beneath them. I try to learn from each new disaster how to change our design techniques, construction practices and building codes to reduce future losses of life and damage. From my perspective, the shock that hit Chile in February was the most important earthquake of the last 100 years.

It was the first mega-quake, its magnitude near 9, to strike a developed country with rigorous building codes. Modern cities full of state-of-the-art buildings were tested by intense ground-shaking that lasted about 120 seconds  compared to about 40 seconds for the 1906 and 20 seconds for the 1989 San Francisco earthquakes, which had magnitudes of 7.9 and 6.9, respectively. Despite Chile’s exacting construction codes, which often exceed those of California and Japan, the performance of numerous high-rise buildings was worryingly poor.

We engineers and seismologists need to gather and study as much data as we can from Chile’s quake. But one thing is already clear: based on the kind of damage that buildings suffered in Chile, tall structures in the earthquake zones of the United States appear to be at much higher risk than we thought. This lesson should be of obvious concern to San Francisco and Los Angeles. But it is actually the Pacific Northwest that is most vulnerable to a mega-quake like Chile’s.

Just off Northern California, Oregon, Washington and British Columbia sits the 600-mile-long Cascadia fault. Like the Nazca tectonic plate that caused the quake and tsunami in Chile, Cascadia can produce temblors with magnitudes of 9 or greater, more powerful than anything we’ve experienced or expect from California’s famous San Andreas fault.