Here, we disentangle a complex disturbance deposit sequence attributed to the ~M 7 1873 CE Brookings earthquake from lower Acorn Woman Lake, Oregon, USA, using sedimentological techniques, computed tomography, and micro-X-ray fluorescence. The lower portion of the sequence is derived from schist bedrock and has characteristics similar to a local landslide deposit, but is present in all cores, suggesting that it is the result of high frequency (>5 Hz) ground motions from a crustal earthquake triggered the landslide. In contrast, the upper portion of the sequence is similar to a deposit attributed to the 1700 CE Cascadia subduction earthquake (two-sigma range of 1680-1780 CE): the base has a higher concentration of light-colored, watershed-sourced silt derived from the delta front followed by a long (2-5 cm) organic tail. The soft lake sediments are more likely to amplify the sustained lower frequency accelerations (

We infer a similar to 2700-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 a disturbance deposit in the historic portion of the sediment cores attributed to the 1700 CE Cascadia earthquake to identify Cascadia earthquake deposits downcore. This deposit is composed of light-colored silt sourced from the delta and has extended organic grading of the deposit tail and a basal contact with evidence of rapid loading or coseismic settling of silt into the organic sediment below. Eight deposits downcore have the characteristics of this deposit. An age-depth model suggests that six of these are temporal correlatives to the largest margin-wide marine turbidite event deposits from Goldfinger et al. (2012) (deposits T1 through T6), whereas the two deposits with some of the characteristics are potential correlatives of smaller deposits T5a and T5b. We use the characteristics of the lower of two deposits inferred to be the result of a crustal earthquake that occurred in 1873 CE to identify similar deposits downcore. As a result, temporal correlatives of T2a and T3a and smaller deposits in the marine record were identified as likely crustal fault earthquakes. These results suggest that small Cascadia landslide-dammed lakes from distances of 100 km inland of the coast with sufficient sedimentation rates (similar to 1-2 cm per decade) and mixed clastic and organic content may be good recorders of subduction earthquakes. Furthermore, southern Cascadia crustal earthquakes likely partially explain the more frequent earthquakes in southern Cascadia and suggest a previously unrecognized hazard in the region.

We compare event deposits from the historical portion of the sedimentary record from Lower Acorn Woman Lake, Oregon, to historical records of regional events to determine if the lake records Cascadia earthquakes. We use the sedimentological characteristics and x-Ray Fluorescence (XRF) provenance of disturbance deposits (labelled A-J) from the historical portion (post 1650 CE) of the record to discriminate between deposit types. We show that earthquake-triggered deposits can be differentiated from flood deposits, and Cascadia earthquakes deposits can be differentiated from other types of earthquake deposits. Event deposit J dates close to 1700 CE (1680-1780 CE) through multiple approaches, suggesting it was the result of shaking from the magnitude (M) 8.8-9.2 1700 CE Cascadia megathrust earthquake. Event deposits H and I are a complex sequence deposited in response to the ~M7.0 1873 CE Brookings earthquake. This earthquake has been previously interpreted to be an intraplate earthquake, is reinterpreted here as the result of an earthquake on a nearby crustal fault. Furthermore, the methods used have uncovered a previously unrecognized crustal earthquake deposit in the tail of deposit J, suggesting a stress relationship between Cascadia earthquakes and crustal earthquakes. These results not only demonstrate the usefulness of these methods to identify cryptic earthquake deposits and discriminate between subduction earthquake and other type of earthquake deposits in sediments from small, Cascadia lakes, but also suggest previously unknown relationships between subduction and crustal earthquakes in Cascadia.

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-colored 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) correlate 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.

Our understanding of the climatic teleconnections that drove ice-age cycles has been limited by a paucity of well-dated tropical records of glaciation that span several glacial–interglacial intervals. Glacial deposits offer discrete snapshots of glacier extent but cannot provide the continuous records required for detailed interhemispheric comparisons. By contrast, lakes located within glaciated catchments can provide continuous archives of upstream glacial activity, but few such records extend beyond the last glacial cycle. Here a piston core from Lake Junín in the uppermost Amazon basin provides the first, to our knowledge, continuous, independently dated archive of tropical glaciation spanning 700,000 years. We find that tropical glaciers tracked changes in global ice volume and followed a clear approximately 100,000-year periodicity. An enhancement in the extent of tropical Andean glaciers relative to global ice volume occurred between 200,000 and 400,000 years ago, during sustained intervals of regionally elevated hydrologic balance that modified the regular approximately 23,000-year pacing of monsoon-driven precipitation. Millennial-scale variations in the extent of tropical Andean glaciers during the last glacial cycle were driven by variations in regional monsoon strength that were linked to temperature perturbations in Greenland ice cores 1 ; these interhemispheric connections may have existed during previous glacial cycles.

The Cascadia subduction zone (CSZ) is an exceptional geologic environment for recording evidence of land-level changes, tsunamis, and ground motion that reveals at least 19 great megathrust earthquakes over the past 10 kyr. Such earthquakes are among the most impactful natural hazards on Earth, transcend national boundaries, and can have global impact.Reducing the societal impacts of future events in the US Pacific Northwest and coastal British Columbia, Canada, requires improved scientific understanding of megathrust earthquake rupture, recurrence, and corresponding hazards. Despite substantial knowledge gained from decades of research, large uncertainties remain about the characteristics and frequencies of past CSZ earthquakes. In this review, we summarize geological, geophysical, and instrumental evidence relevant to understanding megathrust earthquakes along the CSZ and associated uncertainties. We discuss how the evidence constrains various models of great megathrust earthquake recurrence in Cascadia and identify potential paths forward for the earthquake science community. ▪ Despite outstanding geologic records of past megathrust events, large uncertainty of the magnitude and frequency of CSZ earthquakes remains. ▪ This review outlines current knowledge and promising future directions to address outstanding questions on CSZ rupture characteristics and recurrence. ▪ Integration of diverse data sets with attention to the geologic processes that create different records has potential to lead to major progress.

Normalized remanence, a proxy for relative geomagnetic paleointensity, along with radiocarbon and U-Th age constraints, facilitates the generation of a well-constrained chronology for sediments recovered during International Continental Scientific Drilling Program (ICDP) coring of Lake Junín, Peru. The paleomagnetic record of the ∼88 m stratigraphic section from Lake Junín was studied, and rock magnetic variability constrained, through analysis of 109 u-channel samples and 56 discrete samples. Downcore variations in sediment lithology reflect climate and hydrological processes over glacial-interglacial time frames and these changes are strongly reflected in the bulk magnetic properties. Glacial sediments are characterized by higher detrital silt content, higher magnetic susceptibility and magnetic remanence values, and a magnetic coercivity that is characteristic of ferrimagnetic (titano)magnetite and/or maghemite. Interglacial sediments and low lake-level facies are dominated by carbonate lithologies and/or peat horizons that result in lower magnetic concentration values. Sediments with moderately high Natural Remanent Magnetization (NRM) intensity (>1 × 10–3 A/m) have well resolved component directions and inclination values that vary around geocentric axial dipole expectations. This remanence value can be used as a threshold to filter the lowest quality paleomagnetic data from the record. Normalized NRM intensity values are also sensitive to lithologic variability, but following NRM remanence filtering, only the highest quality ferrimagnetic dominated data are retained which then show no coherence with bulk magnetic properties. Constrained by the existing radiocarbon based chronology over the last 50 kyrs and 18 U-Th age constraints that are restricted to five interglacial sediment packages, filtered normalized remanence parameters compare well with global relative paleointensity stacks, suggesting relative variations in geomagnetic intensity are preserved. By adjusting the existing age-depth model we improve the correlation between the Junín normalized intensity record and a well-dated RPI stack and RPI model. We then incorporate these paleomagnetic tie points with the existing radiometric dates using a modeling approach to assess uncertainty and refine the age-depth model for Lake Junín. In combining relative and radiometric dating, the new age-depth model captures glacial-interglacial variations in sedimentation rate and improves the orbital-scale age model for the sediments accumulated in Lake Junín basin over most of the Brunhes.

Reconstruction of high-frequency erosion variability beyond the instrumental record requires well-dated, high-resolution proxies from sediment archives. We used computed tomography (CT) scans of finely laminated silt layers from a lake-sediment record in southwest Oregon to quantify the magnitude of natural landscape erosion events over the last 2000years in order to compare with palaeorecords of climate, forest fire, and seismic triggers. Sedimentation rates were modeled from an age-depth relationship fit through five C-14 dates and the 1964AD Cs-137 peak in which deposition time (yrmm(-1)) varied inversely with the proportion of silt sediment measured by the CT profile. This model resulted in pseudo-annual estimates of silt deposition for the last 2000years. Silt accumulation during the past 80years was strongly correlated with river-discharge at annual and decadal scales, revealing that erosion was highly responsive to precipitation during the logging era (1930-present). Before logging the frequency-magnitude relationship displayed a power-law distribution that is characteristic of complex feedbacks and self-regulating mechanisms. The 100-year and 10-year erosion magnitude estimated in a 99-year moving window varied by 1.7 and 1.0 orders of magnitude, respectively. Decadal erosion magnitude was only moderately positively correlated with a summer temperature reconstruction over the period 900-1900AD. Magnitude of the seven largest events was similar to the cumulative silt accumulation anomaly, suggesting these events returned the system' to the long-term mean rate. Instead, the occurrence of most erosion events was related to fire (silt layers preceded by high charcoal concentration) and earthquakes (the seven thickest layers often match paleo-earthquake dates). Our data show how internal (i.e. sediment production) and external processes (natural fires or more stochastic events such as earthquakes) co-determine erosion regimes at millennial time scales, and the extent to which such processes can be offset by recent large-scale deforestation by logging. Copyright (c) 2018 John Wiley & Sons, Ltd.

The Washington continental margin presents both a classic test of submarine paleoseismology, and an opportunity to explore advancement of the field through analysis of sediment dispersal in a heterogeneous system. New and archive core, bathymetric, backscatter and seismic reflection data from the Washington Cascadia margin show that during high-stand conditions, the northernmost canyons, Barkley, Nitinat, Juan de Fuca (JDF), and to some extent Quillayute are relict systems, with little Holocene recharge. The remaining canyons, Quinault, Grays, Guide, and Willapa, are recharged to a varying degrees by northward transport of Columbia River derived sediment. All systems are nonetheless active conduits for turbidity currents during the Holocene, which are weaker and more restricted than their Pleistocene counterparts. Sedimentologic and CT analysis, supported by radiocarbon ages, micropaleontology, and the Mazama ash datum show that the Holocene sedimentary sequence consists of a series of sand to mud turbidites in the active portions of all systems, interbedded with hemipelagic sediment. However, the Pleistocene Astoria and Nitinat fans are largely inactive in the Holocene, with turbidity current activity limited to the proximal parts of the main channels. Within active systems, the turbidite record is modulated by local landsliding and growth of active folds and faults.

In order to investigate the possibility of a long-term paleoseismic history from offshore sedimentary records in Sumatra, we collected 144 deep-sea sedi-ment cores in the trench and in lower slope piggyback basins of the Sumatra accretionary prism. We used multibeam bathymetry and seismic reflection data to develop an understanding of catchment basins, turbidity current pathways, and depositional styles, as well as to precisely locate our gravity cores, piston cores, Kasten cores, and multicores. We use detailed physical property data, including computed tomographic X-ray, gamma density, magnetic susceptibility, grain-size analysis, faunal analysis, and smear slides, to evaluate the turbidite stratigraphy and sedimentology at each site. We use radiocarbon age control for piggyback basin sites above the carbonate compensation depth, and use Pb-210 and Cs-137 to evaluate the timing of the most recent sedimentary deposits. Using well-log correlation methods and radiometric age control, we test for potential correlations between isolated sites in piggyback basins and the trench.We find evidence for very young surface turbidites along the northern Sumatra margin, most likely emplaced within the past few decades at the seafloor in both the 2004 and 2005 earthquake rupture zones, with no overlying hemipelagic sediment. Based on the young soupy deposits, lack of oxidation, and Pb-210 and C-14 age determinations, we interpret the uppermost turbidite in 21 cores within the 2004 rupture area to have been deposited within a few years of collection in 2007, and most likely as a result of the 2004 moment magnitude (M-w) similar to 9.2 earthquake. The likely 2004 turbidite has a distinctive stacked structure of three major fining-upward sequences observed at several basin and trench sites, similar to the pattern of moment release in the 2004 earthquake. We observe rapid die out of the 2004 and 2005 deposits with distance from the slip zones, from local sources of sediment supply, and in the segment boundary between the slip zones.Many individual turbidites show strong similarities between isolated sites, as well as having similar emplacement times. Based upon radiocarbon age control and lithostratigraphic correlations between isolated basin and trench core sites, we interpret that 43 turbidites can be linked spatially over a distance of similar to 230 km within the southern portion of the 2004 rupture zone. Sampling at deep-water sites isolated from terrestrial and shallow-water sediment sources, as well as potential storm or tsunami wave triggers, limits potential mechanisms for initiating turbidity currents to plate boundary, crustal, or slab earthquakes. Other potential triggers, such as tectonic oversteepening, random self-failures, gas hydrate destabilization, are unlikely to be correlative between any two isolated sites. The most probable explanation for the similarity of timing, turbidite sequences, and individual turbidite structure in isolated basin and trench stratigraphic sequences is a seismogenic origin.The mean emplacement time for turbidites (likely triggered by Great earthquakes, magni-tude > similar to 8) in the 2004 rupture region for the past 6.6 +/- 0.14 k.y. is 160 yr for 43 turbidites. The ages of 8 of the 10 uppermost turbidite deposits, spanning the past similar to 1500 yr, are largely consistent with the terrestrial paleoseismic and/or tsunami records in Thailand, Sumatra, India, and the Anda-man Islands, suggesting either coincidence or a common origin. The mean interseismic time from the turbidite record for this same period is 170 yr, comparable to the similar to 210 yr recurrence for regional tsunami. The turbidite record, at 180 yr (6 events), compares reasonably well to the average for all events on northern Simeulue of 220 yr, and is identical to the tsunami interval of 180 yr for the same time period (6 events). Of the 43 correlated turbidites in the 2004 earthquake region, 13 are well correlated in our cores along strike lengths of 150 km or greater, and satisfy criteria for robustness; 24 turbidites correlated along a shorter strike distance may represent other plate boundary earthquakes of shorter spatial extent and may include turbidite beds sourced from crustal and slab earthquakes.

Text: New and archive cores (N=70), bathymetric, backscatter and sub-bottom data from the Washington margin reveal patterns of Holocene sediment transport and deposition. Barkley, Nitinat, Juan de Fuca (JDF), Quillayute, Grays, Guide, and Willapa Canyons each have different post-glacial mechanisms of loading and dispersal of sediment via turbidity currents. In high-stand conditions, the northern canyons, Barkley, Nitinat, JDF, and Quillayute are mostly relict systems. The remaining canyons, Quinault, Grays, Guide, and Willapa, are recharged to varying degrees by northward transport of Columbia River derived sediment. All systems are nonetheless active conduits for turbidity currents during the Holocene. Sedimentologic and CT analyses, supported by radiocarbon ages, micropaleontology, and the Mazama Ash show that the Holocene sedimentary sequence consists of a series of sand to mud turbidites in the active portions of all systems, interbedded with hemipelagic sediment. The relict systems are finer grained, commonly not visually detected, with Holocene turbidite counts the same as recharged systems. Use of 1960’s core sketches (Atwater) fails to capture the full record, as noted by Barnard (1973). Hydrodynamic models and heavy mineral distributions show that the northern canyon systems (Barkley, Nitinat, JDF, Quillayute) are independent of the southern systems, (Quinault, Guide, Grays, Willapa) during the Holocene. Best fitting flow inversions suggest turbidity currents range in height from 80-170 m, consistent with earlier work and backscatter observations. Mass balancing suggests sediment supplied to the slope canyons and abyssal channels is 4-6 times greater than supplied by recharge to the canyon heads by external sources, strongly indicating autogenic sourcing by earthquakes. Turbidite deposition off Washington is not very sensitive to either sediment supply or slope angle. Lithostratigraphic correlation and age models of Holocene turbidite sequences suggests deposition of ~ 20 Holocene turbidites in most parts of the Canyon systems, with little variation. The explanation most consistent with the data is triggering by a series of 18-20 Holocene earthquakes, in agreement temporal and lithostratigraphic linkages to new marine sites in Canada, as well and land paleoseismic data. . u g a / / : s p t t h confex.com/agu/fm15/t/papers/confirmation.cgi?username=83594&EntryTable=Pa... 1 of 2 unusually late appearance of Mazama ash at T10 in this core 2 based on high resolution magnetic susc. Other data pending weak bioturbated mud turbidites, core outside channel. Interp uncertain. Color change and HP boundary not reached. Color indicates all Holocene all Pleistocene Radiocarbon near HP boundary, approximate time line with very low precision based on log correlation to adjacent T14, ash data not available Color change and HP boundary not reached. Color indicates all Holocene count truncated by erosion 10 Faunal HP boundary data not available 11 upper 5? Beds amalgamated and bioturbated, interp uncertain. Minimum Holocene beds present = 17 12 Color change and HP boundary not reached. Color indicates all Holocene 13 Core bottoms in T11. Count includes T10b, T10f and T4a Table 1. Holocene and Post-Mazama turbidtes, Washington Margin CT observation CT observation Faunal Color Lithostrat. + Reported In Reported by Original ref. Core Location Holocene beds Post Mazama beds H-P Change Radiocarbon phys props. Original Logs Atwater et al., 2014 Holocene/Post MA Post Mazama TT063-18PC Mid JDF Canyon >18 11 X X X X 7/3 4 Barnard (1973) TT063-20PC Mid JDF Canyon/fold 19 16 X X original bulk X 7/4 3 Barnard (1973) NV982-14GC Mid JDF Canyon > 18 na NA X NA X NA not used This paper TT039-06PC Upper JDF Channel 23 16 X X original bulk X 3/2** R likely >6 Carson (1971) TT039-27PC Upper JDF Channel >13 >11 X X original bulk X 7/6** 0? Carson (1971) M9907-05TC/PC Upper JDF Channel >19 18 X X X X 8 3-6 Goldfinger et al., 2012 TT048-08PC Mid JDF Channel >21 16 X X X+original bulk X 15/14 >6 W.D. Barnard (unpub) TT048-09PC Mid JDF Channel >21 16 X X X+original bulk X 15/12** >6 W.D. Barnard (unpub) M9907-012TC/PC Mid JDF Channel 21 14 X X X X 13 13-14 Goldfinger et al., 2012 TT029-28PC Mid JDF Channel > 17 15 X X X X 10/9 likely >6 W.D. Barnard (unpub) TT063-17PC Quillayute Basin 18 14 X X X+original bulk X 7/5 5 W.D. Barnard (unpub) TT053-14PC Quillayute Basin 20 15 X X X+original bulk X 10/8 8 W.D. Barnard (unpub) TT053-18PC Mid Quinault Canyon 19 16 X X X+original bulk X 15/14 14 W.D. Barnard (unpub) NV951-09 Mid Quinault levee >12 >12 NA X NA X NA not used this paper NV967-15 Mid Quinault levee >16 na NA ? NA X NA not used this paper NV951-06 Lower Quinault levee >12 >12 NA ? NA X NA not used this paper TT-063-10PC Lower Quinault levee 23 15 X X original bulk X 16/9 not used Carson (1971) NV967-10 Mid Quillayute levee >17 na NA X NA X NA not used this paper TT053-22PC Upper Willapa Channel >15 15 X X original bulk X 9/9 not used Barnard (1973) TT053-20PC Astoria Canyon 14 14 X X NA X 11/11 not used Barnard (1973) Note: Table 1 has been revised to correspond to the version shown at the meeting, which is slightly di erent that that submitted originally to AGU. 2 Camosun College, Department of Chemistry and Geoscience, Lansdowne Campus, 3100 Foul Bay Rd., Victoria, 1 British Columbia, Canada, V8P 5J2 tark_hamilton@yahoo.com 2 3 Instituto Andaluz de Ciencias de la Tierra (IACT) CSIC Univ. de Granada Campus de Fuentenueva s/n 1 8002 3 Granada, Spain odp@ugr.es