These and other alternating layers of soil and sediments in the slough show that subsidence--perhaps caused by large earthquakes--has occurred at least three times over the past 2,000 years.
(subsidence; perhaps caused; by large earthquakes) (These and other alternating layers of soil and sediments in the slough show that subsidence--perhaps caused by large earthquakes; has occurred; T:at least three times; T:over the past 2,000 years)
subsidence These and other alternating layers of soil and sediments in the slough show that subsidence--perhaps caused by large earthquakes
perhaps caused has occurred
by large earthquakes
T:at least three times T:over the past 2,000 years