Robert Karlin

Paleoearthquakes in the puget sound region recorded in sediments from lake washington, u.s.a.

Holocene sediments in Lake Washington contain a series of turbidites that were episodically deposited throughout the lake. The magnetic signatures of these terrigenous layers are temporally and areally correlatable. Large earthquakes appear to have triggered slumping on the steep basin walls and landslides in the drainage area, resulting in turbidite deposition. One prominent turbidite appears to have been deposited about 1100 years ago as the result of a large earthquake. Downcore susceptibility patterns suggest that near-simultaneous slumping occurred in at least three separate locations, two of which now contain submerged forests. Several other large earthquakes may have occurred in the last 3000 years.

A sixty thousand year paleomagnetic record from Gulf of California sediments: secular variation, late Quaternary excursions and geomagnetic implications

A unique inclination record of geomagnetic secular variation for the past 60, 000 years (60 ka) has been obtained from continuously deposited sediments in the Gulf of California, recovered during Deep Sea Drilling Project (DSDP) Leg 64 by hydraulic piston coring at Site 480. The chronology of Hole 480 was determined by δ18O stratigraphy and varve counts, indicating sedimentation rates approaching 1 m/ka. The paleomagnetic results of the upper 49 m show: (1) The average inclination over this interval is identical to the geocentric axial dipole value at the sampling site. (2) Excursion directions occur between about 53 and 22 ka before present (BP). During this time, the geomagnetic field was generally “noisier” than in the overlying and underlying sections, with greater dispersion of the inclination. (3) The Laschamp excursion was apparently recorded at Hole 480 between about 51 and 49 ka BP and the Mono Lake excursion between about 29 and 26 ka BP. In addition, a narrow 0.3–0.4 m zone near 23 ka BP has a very similar paleomagnetic signature as the excursion observed at Summer Lake, Oregon [1], and we suggest that the Summer Lake is distinct from and younger than the Mono Lake excursion by 3–5 ka and of considerably shorter duration, lasting no more than a few hundred years. (4) Recurring inclination fluctuations were identified at Site 480, characterized by end points with steep inclinations and shallow intermediate value(s), as compared with the geocentric axial dipole. The inclination cycles are particularly apparent from 54 to 24 ka BP with a characteristic period of about 4.4 ka. (5) The “noisier” inclination record between 54 and 24 ka BP might be related to the generally reduced dipole moment between about 20 and 50 ka, and particularly low paleointensities for the Laschamp and Mono Lake excursions.

Holocene landslides and a 3500-year record of Pacific Northwest earthquakes from sediments in Lake Washington

Lake Washington, which forms the eastern boundary of Seattle, is located in a tectonically active area containing several strands of the Seattle fault. High-resolution seismic reflection profiling, sidescan swath imagery, and sediment coring were used to define deformation of Holocene lake sediments and the distribution, geometry, age, and causes of submarine landslides. Numerous large block slides, sediment slumps, and debris flows are present throughout the lake, and large landslides obscure the surficial structure of Seattle fault strands as they pass through the lake. In addition, most bays along the lake margin are the headwalls of large submarine slides. Submerged forests show evidence of deep- seated block failures that have exposed glacial sediments and Tertiary rocks. The massive submarine block slides, and retrogressive submarine slope failures were triggered most likely by large (m b >7) earthquakes on the Seattle fault and/or large to great (m b >8) temblors occurring elsewhere in Cascadia. Buried landslides suggest that submarine slope failures and mass wasting occurred more than once in the last 11,000 yr. Sediments in Lake Washington preserve a record of episodic deposition of turbidites possibly caused by seismically induced submarine landslides. Magnetic susceptibility profiles on 36 gravity cores show a characteristic series of magnetic peaks that can be traced throughout the lake. X- radiography and grain size analyses suggest that the magnetic peaks represent anomalous detrital layers that in some cases are turbidites. The areal extent and magnetic signatures of many of the deposits suggest multiple sources, which is consistent with numerous local landslides caused by large earthquakes. Radiocarbon dating and correlation of the downcore magnetic profiles establish a sediment record in which episodic sedimentary disturbances occurred seven times in the last 3500 yr. If these deposits are seismically induced turbidites (seismites), then large earthquakes have occurred about every 300–500 yr in the Puget Sound region.

Carbonate Variations in the Northeast Pacific during the Late Quaternary

Quaternary glacial/interglacial changes in the carbonate compensation depth (CCD) have been determined from core suites in three regions of the NE Pacific. The cores have sedimentation rates ranging from 1.6 to 16 cm/kyr, based on oxygen isotope, radiocarbon, and/or carbonate stratigraphies. Carbonate values are higher in glacial than interglacial times and generally follow a pattern similar to that of the central equatorial Pacific. The sediments carbonate profiles can be readily intercorrelated, allowing the construction of a regional carbonate stratigraphy. The extent of carbonate preservation is very sensitive to small changes in water depth but does not depend on geographic location. A depth transect of cores off northern California and Oregon provides a detailed record of glacial/interglacial shifts in the CCD through time. During the late Holocene, intensified carbonate dissolution at ∼7 ka is coincident with shifts in continental climatic indicators and may suggest the onset of the modern upwelling regime along the NW U.S. margin. During the last 45 ka the CCD has migrated more than 1800 m between glacial and interglacial times. Although carbonate patterns are similar to those in the equatorial Pacific, the amplitude of the carbonate fluctuations is much greater in the northeast Pacific. This suggests that regional mechanisms, such as glacial deepwater formation or enhanced dissolution due to interglacial noncarbonate productivity related to coastal upwelling, may modulate carbon cycling.

Carbonate deposition and benthicδ13C in the subarctic Pacific: implications for changes of the oceanic carbonate system during the past 750,000 years

Abstract Carbonate deposition at two core sites in the subarctic Pacific (48°N, 133°W; 2.9 km and 3.7 km water depth) follows the standard Pacific carbonate cycles, with glacial values being increased over interglacial values. Benthicδ13C follows the global trend; that is, glacial values are more negative than interglacial values. Comparison with the benthicδ13C record of North Atlantic DSDP Site 552 (56°N, 23°W; 2.3 km water depth) shows the North Pacific records to be nearly in phase with and continuously more negative relative to the North Atlantic record. This suggests that concentrations of∑CO2(org) were permanently higher in the North Pacific than in the North Atlantic during the past 750,000 years conceivably supporting the hypothesis that there was no deep-water forming in the late Pleistocene North Pacific. Whereas one would expect that the North Pacific deep waters were continuously more corrosive to carbonates than deep waters in the North Atlantic, carbonate deposition at the deep North Pacific core sites is enhanced during glacial periods, and occasionally higher than at shallow North Atlantic Site 552 even though Site 552 was probably above lysocline-depth during most of the late Pleistocene. This apparent paradox can be resolved only by invoking an increase in alkalinity in the glacial North Pacific which would have increased the degree of carbonate ion saturation and thereby improved the state of carbonate preservation.

New Constraints on Deformation, Slip Rate, and Timing of the Most Recent Earthquake on the West Tahoe-Dollar Point Fault, Lake Tahoe Basin, California

High-resolution seismic compressed high intensity Radar pulse (CHIRP) data and piston cores acquired in Fallen Leaf Lake (FLL) and Lake Tahoe provide new paleoseismic constraints on the West Tahoe-Dollar Point fault (WTDPF), the western- most normal fault in the Lake Tahoe Basin, California. Paleoearthquake records along three sections of the WTDPF are investigated to determine the magnitude and recency of coseismic slip. CHIRP profiles image vertically offset and folded strata along the southern and central sections that record deformation associated with the most recent event (MRE) on the WTDPF. Three faults are imaged beneath FLL, and the maximum vertical offset observed across the primary trace of the WTDPF is ∼3:7 m. Coregis- tered piston cores in FLL recovered sediment and organic material above and below the MRE horizon. Radiocarbon dating of organic material constrained the age of the MRE to be between 3.6 and 4.9 k.y. B.P., with a preferred age of 4.1-4.5 k.y. B.P. In Lake Tahoe near Rubicon Point, approximately 2.0 m of vertical offset is observed across the WTDPF. Based on nearby core data, the timing of this offset occurred be- tween ∼3-10 k:y: B.P., which is consistent with the MRE age in FLL. Offset of Tioga- aged glacial deposits provides a long-term record of vertical deformation on the WTDPF since ∼13-14 k:y: B.P., yielding a slip rate of 0:4-0:8 mm=yr. In summary, the slip rate and earthquake potential along the WTDPF is comparable to the nearby Genoa fault, making it the most active and potentially hazardous fault in the Lake Tahoe Basin.

Holocene subaqueous paleoseismology of Lake Tahoe

Gravity-flow deposits recovered in a suite of sediment cores in Lake Tahoe were examined to determine if the event deposits were triggered by strong shaking from earthquakes on active faults within and in close proximity to the Lake Tahoe Basin. The acoustic character and distribution of individual lacustrine deposits as well as potential source regions were constrained by high-resolution seismic Chirp reflection and multibeam bathymetric data. Between 14 and 17 Holocene event deposits have been identified in Lake Tahoe, and examination of their source areas suggests they originated from different initiation points along the steep margin, with some being synchronous around the basin, as opposed to flood-related deposits. Lithologic characteristics, magnetic susceptibility, carbon and nitrogen isotopic signatures, opal content, and 14 C dating indicate that these event deposits are reworked lacustrine material. Radiocarbon dates indicate that the emplacement of these event deposit sediments correlates well with the late Holocene paleoseismic earthquake record developed for the Tahoe Basin. When taken alone, the causality of these events may appear ambiguous, but when the evidence is examined comprehensively, it suggests that strong shaking may likely have been the primary trigger for many of the event deposits observed in the lake throughout the Holocene. For example, four event deposits are assigned to Tahoe Basin faults. The most recent earthquakes occurred on the Incline Village fault (between 630 and 120 cal. yr B.P.); the southern segment of the West Tahoe fault (between 4510 and 4070 cal. yr B.P.); on the central and northern segments of the West Tahoe fault (5600–5330 cal. yr B.P.); and on the West Tahoe fault (between 7890 and 7190 cal. yr B.P.). The oldest of the four associated Tahoe Basin events coincides with the beginning of an extended period when Lake Tahoe was likely not spilling or spilling intermittently, and this suggests that active faulting and footwall uplift cut off the outlet at this time, exaggerating drought conditions downstream. Likewise, the event between 5600 and 5330 cal. yr B.P. on the West Tahoe fault may have exaggerated a smaller drought reflected downstream in Pyramid Lake. This event may also be the most recent event (MRE) on the largest segment of the West Tahoe fault. If correct, the period since the last rupture is approximately twice the estimated average recurrence interval for the Rubicon segment of the West Tahoe fault. A more complete Holocene record of strong shaking greatly extends the paleoseismic record in the region and indicates a combined recurrence interval of between 750 and 800 yr for all faults in the region.

A history of Pacific Northwest earthquakes recorded in Holocene sediments from Lake Washington

Large earthquakes can trigger slumping of the steep walls of lake basins and landslides in the drainage area, resulting in turbidite deposition in the lake and increased detrital flux from inlets. Holocene sediments in piston cores from Lake Washington contain a series of terrigenous layers that were episodically deposited in the lake. Sedimentological, geochemical, and paleomagnetic analyses on nine piston cores show that the detrital layers are temporally and areally correlatable, indicating basinwide disruptions. These layers are opaque on X-radiographs, are coincident with magnetic susceptibility peaks, have abundant aluminosilicate minerals, are relatively coarse grained, and have low organic carbon and biogenic silica contents. The thicknesses and geographic distributions of the layers suggest that they are not due to floods or delta destabilization. Side scan swath imagery and subbottom profiling show that large slumps, subaqueous landslides, and debris flows are common along the margins of the lake. A detailed chronology, established from 21 radiocarbon ages on five cores, show that a prominent turbidite was deposited about 1000–1100 years ago. This turbidite apparently was triggered by a large earthquake that probably occurred on the Seattle fault. Other depositional events in the sediment record at 1500–1700, 2400–2500, and 2800–3200 years ago coincide with periods of landsliding that have been previously inferred from the dating of drowned trees in the lake. More than 30 depositional events have occurred in the last 12,000 years and 21 disturbances have occurred since the deposition of the Mazama ash about 7,600 years ago. If all the events are due to earthquakes, the Puget Sound region has been subject to major shaking every 300 to 400 years. The strong intensities needed to trigger subaqueous slides may not be generated by just local sources such as the Seattle fault but could also be caused by great subduction earthquakes occurring along the coast.

Paleoseismic history of the Fallen Leaf segment of the West Tahoe–Dollar Point fault reconstructed from slide deposits in the Lake Tahoe Basin, California-Nevada

The West Tahoe–Dollar Point fault (WTDPF) extends along the western margin of the Lake Tahoe Basin (northern Sierra Nevada, western United States) and is characterized as its most hazardous fault. Fallen Leaf Lake, Cascade Lake, and Emerald Bay are three subbasins of the Lake Tahoe Basin, located south of Lake Tahoe, and provide an opportunity to image primary earthquake deformation along the WTDPF and associated landslide deposits. Here we present results from high-resolution seismic Chirp (compressed high intensity radar pulse) surveys in Fallen Leaf Lake and Cascade Lake, multibeam bathymetry coverage of Fallen Leaf Lake, onshore Lidar (light detection and ranging) data for the southern Lake Tahoe Basin, and radiocarbon dates from piston cores in Fallen Leaf Lake and Emerald Bay. Slide deposits imaged beneath Fallen Leaf Lake appear to be synchronous with slides in Lake Tahoe, Emerald Bay, and Cascade Lake. The temporal correlation of slides between multiple basins suggests triggering by earthquakes on the WTDPF system. If this correlation is correct, we postulate a recurrence interval of ∼3–4 k.y. for large earthquakes on the Fallen Leaf Lake segment of the WTDPF, and the time since the most recent event (∼4.5 k.y. ago) exceeds this recurrence time. In addition, Chirp data beneath Cascade Lake image strands of the WTDPF offsetting the lake floor as much as ∼7.5 m. The Cascade Lake data combined with onshore Lidar allow us to map the WTDPF continuously between Fallen Leaf Lake and Cascade Lake. This improved mapping of the WTDPF reveals the fault geometry and architecture south of Lake Tahoe and improves the geohazard assessment of the region.

Recent faulting in western Nevada revealed by multi-scale seismic reflection

Roxanna N. Frary∗†, John N. Louie†, William J. Stephenson‡, Jackson K. Odum‡, Annie Kell†, Amy Eisses†, Graham M. Kent†, Neal W. Driscoll§, Robert Karlin¶, Robert L. Baskin‖, Satish Pullammanappallil∗∗, Lee M. Liberty†† †Nevada Seismological Laboratory, University of Nevada ‡United States Geological Survey, Golden, Colorado §Scripps Institution of Oceanography, University of California, San Diego ¶Department of Geological Sciences and Engineering, University of Nevada ‖United States Geological Survey, West Valley City, Utah ∗∗Optim, Reno, Nevada ††Center for the Geophysical Investigation of the Shallow Subsurface, Boise State University