Late resonant response at Texcoco, Valley of Mexico, during distant earthquakes

Recordings of the ground motion induced by two shallow (15–25km deep), distant (300 and 605km) earthquakes made on deep, soft lacustrine sediments at Texcoco, Valley of Mexico, show a late monochromatic response at 0.48Hz. Data from a strong-motion recorder array show that this late response is consistent with slow (60m/s group velocity) Rayleigh waves generated near the 6km distant soft/stiff soil interface of the ex-lake surface margin. It is concluded that the excitation of local Rayleigh waves in soft soil deposits by arriving earthquake ground motion provides one mechanism to explain the prolonged duration of resonant motion on soft soils, and hence the extreme damage often associated with soft soils responding to distant earthquakes.