Fast Identification of Near-Trench Earthquakes along the Mexican Subduction Zone Based on Characteristics of Ground Motion in Mexico City

摘要

We explore the versatility of three parameters computed from recordings at station CU, located in Mexico City, similar to 300-600 km from the trench, for quick detection (<= 7 min after the origin time) of near-trench earthquakes for potential use in tsunami warning. The parameters are (1) E-R, the ratio of total to high-frequency energy, (2) Sa*(6), the pseudoacceleration response spectrum with 5% damping at 6 s normalized by peak ground acceleration (PGA), and (3) R-ESN, the PGA residual with respect to a newly derived ground-motion prediction equation at CU. Because neartrench earthquakes are relatively deficient in high-frequency radiation, we expect E-R and Sa*(6) to be relatively large and R-ESN to be negative for such events. Tests on CU recordings of 65 interface earthquakes occurring along the Mexican subduction zone (4.8 <= M-w <= 8.0; 270 <= R <= 615 km) show that if E-R >= 100, Sa*(6) >= 0.70, and R-ESN <= 0, then the earthquake is near the trench. Such an event has greater tsunami potential and produces low acceleration. Few misidentifications and missed events are probably a consequence of poor location, although unusual depth and source characteristics may also be responsible in some cases.