Field observations from 47 caves in the central and eastern USA (CEUS) show that uranium-series dating of earthquake-damaged speleothems (cave formations) and of quake-triggered new speleothem growth can yield paleoearthquake chronologies in seismogenic areas where inter-event times may span 103 – 104 years. Conventional paleoseismic techniques (trenching to date disrupted strata or liquefaction effects to identify prior earthquakes) work where faults rupture to the ground surface and sedimentation preserves events. Other techniques are needed in the CEUS, where seismogenic faults tend not to daylight and lack prominent geomorphic expression. Caves are common in the CEUS; as landscape features, caves persist for millions of years and contain speleothems that can be impacted by strong ground shaking. Speleothems commonly incorporate 0.1-10 ppm 234U at deposition that decays and produces a daughter, 230Th. With proper samples, U-series dating can span 350K-500K years with precision of a few percent (comparable to 14C). Reconnaissance of 10 caves in IL and IN and 14 caves between Knoxville, TN and the Shenandoah Valley, VA shows speleothem breakage and new-growth initiation effects are common. Moreover, the sizes of broken speleothems and sizes of post-breakage speleothem growth increase eastward from the Ozarks to the Appalachians; we infer an eastwardly increase in inter-event times of major earthquakes. Despite challenges in dating speleothems with complex histories and avoiding breakage owing to non-seismic causes, caves that contain time-synchronous effects across geographic areas offer promise for recognizing paleoearthquakes where conventional paleoseismology may not succeed.
|Original language||English (US)|
|Title of host publication||Seismological Research Letters|
|Publisher||Seismological Society of America|
|State||Published - 2015|