Preprints
https://doi.org/10.21203/rs.3.rs-2277419/v2
https://doi.org/10.21203/rs.3.rs-2277419/v2
24 Aug 2023
 | 24 Aug 2023

A 2700-yr record of Cascadia megathrust and crustal/slab earthquakes from Upper and Lower Squaw Lakes, Oregon

Ann Elizabeth Morey and Chris Goldfinger

Abstract. We infer a ~2,700-year history of Cascadia megathrust and other earthquakes from two small mountain lakes located 100 km inland of the coast near the California/Oregon border. We use the characteristics of disturbance deposits in the historic portion of the sediment cores from the lower lake to identify a deposit from the 1700 CE Cascadia earthquake (deposit J). This deposit is composed of light-coloured silt (indicating it is enriched in watershed-sourced sediment), without visible mica grains (which would indicate a lake bedrock source), organic grading of the deposit tail, and a basal contact with evidence of rapid loading.

Seven deposits downcore have some of the characteristics of deposit J. An age-depth model suggests that the five deposits most similar to deposit J (including deposit J) are temporal correlatives to the largest margin-wide marine turbidite event deposits from Goldfinger et al., 2012, (T1, T2, T3, T4, T5 and T6), whereas the two deposits with some of the characteristics are potential correlatives of smaller turbidites T5a and T5b. Other thinner deposits are temporal correlatives of T2a and T3a and other smaller deposits of uncertain origin. Lake core physical property data can be correlated to those from other regional lake records and offshore cores. These results suggest that small Cascadia lakes with sufficient sedimentation rates (~1–2 cm/decade) with mixed clastic and organic sedimentation may be good recorders of earthquakes, that subduction earthquake deposits are different from those from other types of earthquake deposits and deposits from other types of disturbances, such as floods.

Ann Elizabeth Morey and Chris Goldfinger

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1638', Anonymous Referee #1, 18 Sep 2023
    • AC2: 'Reply on RC1', Ann Morey, 27 Nov 2023
  • AC1: 'Comment on egusphere-2023-1638', Ann Morey, 03 Oct 2023
  • RC2: 'Comment on egusphere-2023-1638', Amotz Agnon, 07 Oct 2023
    • AC3: 'Reply on RC2', Ann Morey, 27 Nov 2023
Ann Elizabeth Morey and Chris Goldfinger
Ann Elizabeth Morey and Chris Goldfinger

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Short summary
This study uses the characteristics from a deposit attributed to the 1700 CE Cascadia earthquake to identify other subduction earthquake deposits in sediments from two lakes located near the California/Oregon border. Seven deposits were identified in these records and an age-depth model suggests that these correlate in time to the largest Cascadia earthquakes preserved in the offshore record suggesting that inland lakes can be good recorders of Cascadia earthquakes.