Geology topics

Kelin Wang

Publications and source records attributed to Kelin Wang.

12 recordsLinked to original sources

USGS2021

Global resorption efficiencies of trace elements in leaves of terrestrial plants

Leaf nutrient resorption is a critical nutrient conservation strategy. Previous studies focus mainly on resorption patterns of macronutrients, but resorption patterns of trace elements remain poorly understood. A meta-analysis was conducted to explore the general patterns of the leaf resorption of eight trace elements [i.e. copper (Cu), molybdenum (Mo), zinc (Zn), boron (B), manganese (Mn), sodium (Na), aluminium (Al) and iron (Fe)], and a macronutrient [i.e. sulphur (S)] using data collected from 53 published studies. Sulphur (49.6%) had the highest average resorption efficiency followed by Cu (30.3%), Mo (29.5%), Zn (19.5%) and B (17.6%). Two structural elements, Na and Mn, were not resorbed, whereas two potentially toxic elements, Al (−55.6%) and Fe (−25.4%), were accumulated in senesced leaves. Both climatic factors and growth types affected leaf nutrient resorption efficiency, but the magnitudes and directions of the effects differed greatly between S and the trace elements. The resorption efficiencies of S, Cu, Mo and Zn decreased as leaf nutrient concentrations increased, but the structural or potentially toxic elements (i.e. B, Mn, Na, Fe and Al) presented no response or opposite trends. Our results provide global mean resorption efficiencies of trace elements for the first time, and highlight that structural and potentially toxic elements have relatively lower or no leaf resorption, which should be fully considered in biogeochemical models.

Functional Ecology↗

USGS2021

Coexistence of multiple leaf nutrient resorption strategies in a single ecosystem

Leaf resorption is critical for considerations of how plants use and recycle nutrients, but fundamental unknowns remain regarding the controls over plant nutrient resorption. Empirical studies suggest at least three basic types of resorption control, including (i) stoichiometric control, (ii) nutrient limitation control, and (iii) nutrient concentration control strategies. However, which strategies are adopted in given conditions and whether multiple strategies coexist in an ecosystem are still open questions. To address these unknowns, leaf nitrogen (N) and phosphorus (P) resorption efficiency (NRE and PRE) and proficiency were measured for seven woody species at a nutrient-rich but potentially N-limited secondary forest and a nutrient-poor and potentially P-limited secondary forest. NRE was higher in the N-limited forest while PRE was higher in the P-limited forest, suggesting that plants responded to nutrient limitation with preferential resorption of the more limiting nutrient. NRE:PRE was positively related to leaf N:P ratios within each forest, demonstrating a role for stoichiometric control. Nutrient concentration controls were also found, with higher nutrient resorption proficiency in the nutrient-poor forest than in the nutrient-rich forest. The controls of stoichiometry and nutrient concentration were community-wide, but the nutrient limitation control was species-specific. Our results highlight the coexistence of multiple nutrient resorption strategies in a single ecosystem, and suggest these strategies are scale-dependent.

Science of the Total Environment↗

USGS2021

Toward an integrative geological and geophysical view of Cascadia subduction zone earthquakes

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 U.S. 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.

British Columbia, Oregon, Washington↗

USGS2017

New constraints on coseismic slip during southern Cascadia subduction zone earthquakes over the past 4600 years implied by tsunami deposits and marine turbidites

Forecasting earthquake and tsunami hazards along the southern Cascadia subduction zone is complicated by uncertainties in the amount of megathrust fault slip during past ruptures. Here, we estimate slip on hypothetical ruptures of the southern part of the megathrust through comparisons of late Holocene Cascadia earthquake histories derived from tsunami deposits on land and marine turbidites offshore. Bradley Lake in southern Oregon lies ~600 m landward of the shoreline and contains deposits from 12 tsunamis in the past 4600 years. Tsunami simulations that overtop the 6-m-high lake outlet, generated by ruptures with most slip south of Cape Blanco, require release of at least as much strain on the megathrust as would accumulate in 430–640 years (>15–22 m). Such high slip is inconsistent with global seismic data for a rupture ~300-km long and slip deficits over the past ~4700 years on the southern Cascadia subduction zone. Assuming slip deficits accumulated during the time intervals between marine turbidites, up to 8 of 12 tsunami inundations at the lake are predicted from a marine core site 170 km north of the lake (at Hydrate Ridge) compared to 4 of 12 when using a core site ~80 km south (at Rogue Apron). Longer time intervals between turbidites at Hydrate Ridge imply larger slip deficits compared to Rogue Apron. The different inundations predicted by the two records suggest that Hydrate Ridge records subduction ruptures that extend past both Rogue Apron and Bradley Lake. We also show how turbidite-based estimates of CSZ rupture length relate to tsunami source scenarios for probabilistic tsunami hazard assessments consistent with lake inundations over the last ~4600 years.

Oregon↗

USGS2017

Microfossil measures of rapid sea-level rise: Timing of response of two microfossil groups to a sudden tidal-flooding experiment in Cascadia

Comparisons of pre-earthquake and post-earthquake microfossils in tidal sequences are accurate means to measure coastal subsidence during past subduction earthquakes, but the amount of subsidence is uncertain, because the response times of fossil taxa to coseismic relative sea-level (RSL) rise are unknown. We measured the response of diatoms and foraminifera to restoration of a salt marsh in southern Oregon, USA. Tidal flooding following dike removal caused an RSL rise of ∼1 m, as might occur by coseismic subsidence during momentum magnitude (M w ) 8.1–8.8 earthquakes on this section of the Cascadia subduction zone. Less than two weeks after dike removal, diatoms colonized low marsh and tidal flats in large numbers, showing that they can record seismically induced subsidence soon after earthquakes. In contrast, low-marsh foraminifera took at least 11 months to appear in sizeable numbers. Where subsidence measured with diatoms and foraminifera differs, their different response times may provide an estimate of postseismic vertical deformation in the months following past megathrust earthquakes.

Oregon↗

USGS2015

Intertidal biological indicators of coseismic subsidence during the Mw 7.8 Haida Gwaii, Canada, earthquake

The 28 October 2012 M w 7.8 Haida Gwaii earthquake was a megathrust earthquake along the very obliquely convergent Queen Charlotte margin of British Columbia, Canada. Coseismic deformation is not well constrained by geodesy, with only six Global Positioning System (GPS) sites and two tide gauge stations within 250 km of the rupture area. To better constrain vertical coseismic deformation, we measured the upper growth limits of two sessile intertidal organisms, which are controlled by physical conditions, relative to sea level at 25 sites 5 months after the earthquake. We measured the positions of rockweed ( Fucus distichus , 617 observations) and the common acorn barnacle ( Balanus balanoides , 686 observations). The study focused on the western side of the islands where rupture models indicated that the greatest amount of vertical displacement, but we also investigated sites well away from the inferred rupture area to provide a control on the upper limit of the organisms unaffected by vertical displacement. We also made 322 measurements of sea level to relate the growth limits to a tidal datum using the TPXO7.2 tidal model, rather than ellipsoid heights determined by GPS. Three methods of examining the data all indicate 0.4–0.6 m subsidence along the western coast of Moresby Island as a result of the 28 October 2012 Haida Gwaii earthquake. Our data are, within the errors, consistent with data from two campaign GPS sites along the west coast of Haida Gwaii and with rupture models that indicate megathrust rupture offshore, but not beneath, the islands.

Bulletin of the Seismological Society of America↗

USGS2014

A large mantle water source for the northern San Andreas Fault System: A ghost of subduction past

Recent research indicates that the shallow mantle of the Cascadia subduction margin under near-coastal Pacific Northwest U.S. is cold and partially serpentinized, storing large quantities of water in this wedge-shaped region. Such a wedge probably formed to the south in California during an earlier period of subduction. We show by numerical modeling that after subduction ceased with the creation of the San Andreas Fault System (SAFS), the mantle wedge warmed, slowly releasing its water over a period of more than 25 Ma by serpentine dehydration into the crust above. This deep, long-term water source could facilitate fault slip in San Andreas System at low shear stresses by raising pore pressures in a broad region above the wedge. Moreover, the location and breadth of the water release from this model gives insights into the position and breadth of the SAFS. Such a mantle source of water also likely plays a role in the occurrence of Non-Volcanic Tremor (NVT) that has been reported along the SAFS in central California. This process of water release from mantle depths could also mobilize mantle serpentinite from the wedge above the dehydration front, permitting upward emplacement of serpentinite bodies by faulting or by diapiric ascent. Specimens of serpentinite collected from tectonically emplaced serpentinite blocks along the SAFS show mineralogical and structural evidence of high fluid pressures during ascent from depth. Serpentinite dehydration may also lead to tectonic mobility along other plate boundaries that succeed subduction, such as other continental transforms, collision zones, or along present-day subduction zones where spreading centers are subducting.

California↗

USGS2014

Tsunami impact to Washington and northern Oregon from segment ruptures on the southern Cascadia subduction zone

This paper explores the size and arrival of tsunamis in Oregon and Washington from the most likely partial ruptures of the Cascadia subduction zone (CSZ) in order to determine (1) how quickly tsunami height declines away from sources, (2) evacuation time before significant inundation, and (3) extent of felt shaking that would trigger evacuation. According to interpretations of offshore turbidite deposits, the most frequent partial ruptures are of the southern CSZ. Combined recurrence of ruptures extending ~490 km from Cape Mendocino, California, to Waldport, Oregon (segment C) and ~320 km from Cape Mendocino to Cape Blanco, Oregon (segment D), is ~530 years. This recurrence is similar to frequency of full-margin ruptures on the CSZ inferred from paleoseismic data and to frequency of the largest distant tsunami sources threatening Washington and Oregon, ~M w 9.2 earthquakes from the Gulf of Alaska. Simulated segment C and D ruptures produce relatively low-amplitude tsunamis north of source areas, even for extreme (20 m) peak slip on segment C. More than ~70 km north of segments C and D, the first tsunami arrival at the 10-m water depth has an amplitude of <1.9 m. The largest waves are trapped edge waves with amplitude ≤4.2 m that arrive ≥2 h after the earthquake. MM V–VI shaking could trigger evacuation of educated populaces as far north as Newport, Oregon for segment D events and Grays Harbor, Washington for segment C events. The NOAA and local warning systems will be the only warning at greater distances from sources.

Oregon;Washington↗

USGS2013

Heterogeneous rupture in the great Cascadia earthquake of 1700 inferred from coastal subsidence estimates

Past earthquake rupture models used to explain paleoseismic estimates of coastal subsidence during the great A.D. 1700 Cascadia earthquake have assumed a uniform slip distribution along the megathrust. Here we infer heterogeneous slip for the Cascadia margin in A.D. 1700 that is analogous to slip distributions during instrumentally recorded great subduction earthquakes worldwide. The assumption of uniform distribution in previous rupture models was due partly to the large uncertainties of then available paleoseismic data used to constrain the models. In this work, we use more precise estimates of subsidence in 1700 from detailed tidal microfossil studies. We develop a 3-D elastic dislocation model that allows the slip to vary both along strike and in the dip direction. Despite uncertainties in the updip and downdip slip extensions, the more precise subsidence estimates are best explained by a model with along-strike slip heterogeneity, with multiple patches of high-moment release separated by areas of low-moment release. For example, in A.D. 1700, there was very little slip near Alsea Bay, Oregon (~44.4°N), an area that coincides with a segment boundary previously suggested on the basis of gravity anomalies. A probable subducting seamount in this area may be responsible for impeding rupture during great earthquakes. Our results highlight the need for more precise, high-quality estimates of subsidence or uplift during prehistoric earthquakes from the coasts of southern British Columbia, northern Washington (north of 47°N), southernmost Oregon, and northern California (south of 43°N), where slip distributions of prehistoric earthquakes are poorly constrained.

British Columbia;Washington;Oregon;California↗

USGS2013

Simulated tsunami inundation for a range of Cascadia megathrust earthquake scenarios at Bandon, Oregon, USA

Characterizations of tsunami hazards along the Cascadia subduction zone hinge on uncertainties in megathrust rupture models used for simulating tsunami inundation. To explore these uncertainties, we constructed 15 megathrust earthquake scenarios using rupture models that supply the initial conditions for tsunami simulations at Bandon, Oregon. Tsunami inundation varies with the amount and distribution of fault slip assigned to rupture models, including models where slip is partitioned to a splay fault in the accretionary wedge and models that vary the updip limit of slip on a buried fault. Constraints on fault slip come from onshore and offshore paleoseismological evidence. We rank each rupture model using a logic tree that evaluates a model’s consistency with geological and geophysical data. The scenarios provide inputs to a hydrodynamic model, SELFE, used to simulate tsunami generation, propagation, and inundation on unstructured grids with <5–15 m resolution in coastal areas. Tsunami simulations delineate the likelihood that Cascadia tsunamis will exceed mapped inundation lines. Maximum wave elevations at the shoreline varied from ∼4 m to 25 m for earthquakes with 9–44 m slip and Mw 8.7–9.2. Simulated tsunami inundation agrees with sparse deposits left by the A.D. 1700 and older tsunamis. Tsunami simulations for large (22–30 m slip) and medium (14–19 m slip) splay fault scenarios encompass 80%–95% of all inundation scenarios and provide reasonable guidelines for land-use planning and coastal development. The maximum tsunami inundation simulated for the greatest splay fault scenario (36–44 m slip) can help to guide development of local tsunami evacuation zones.

Oregon↗

USGS2011

Observing the Greatest Earthquakes: AGU Chapman Conference on Giant Earthquakes and Their Tsunamis: Viña del Mar and Valparaíso, Chile, 16–20 May 2010

An AGU Chapman Conference commemorated the fiftieth anniversary of the 1960 M 9.5 Chile earthquake. Participants reexamined this earthquake, the largest ever recorded instrumentally, and compared it with Chile's February 2010 M 8.8 earthquake. They also addressed the giant earthquake potential of subduction zones worldwide and strategies for reducing losses due to tsunamis. The conference drew 96 participants from 18 countries, and it reached out to public audiences in Chile.

Eos, Earth and Space Science News↗

USGS2002

The Cascadia Subduction Zone and related subduction systems: Seismic structure, intraslab earthquakes and processes, and earthquake hazards

The following report is the principal product of an international workshop titled “Intraslab Earthquakes in the Cascadia Subduction System: Science and Hazards” and was sponsored by the U.S. Geological Survey, the Geological Survey of Canada and the University of Victoria. This meeting was held at the University of Victoria’s Dunsmuir Lodge, Vancouver Island, British Columbia, Canada on September 18–21, 2000 and brought 46 participants from the U.S., Canada, Latin America and Japan. This gathering was organized to bring together active research investigators in the science of subduction and intraslab earthquake hazards. Special emphasis was given to “warm-slab” subduction systems, i.e., those systems involving young oceanic lithosphere subducting at moderate to slow rates, such as the Cascadia system in the U.S. and Canada, and the Nankai system in Japan. All the speakers and poster presenters provided abstracts of their presentations that were a made available in an abstract volume at the workshop. Most of the authors subsequently provided full articles or extended abstracts for this volume on the topics that they discussed at the workshop. Where updated versions were not provided, the original workshop abstracts have been included. By organizing this workshop and assembling this volume, our aim is to provide a global perspective on the science of warm-slab subduction, to thereby advance our understanding of internal slab processes and to use this understanding to improve appraisals of the hazards associated with large intraslab earthquakes in the Cascadia system. These events have been the most frequent and damaging earthquakes in western Washington State over the last century. As if to underscore this fact, just six months after this workshop was held, the magnitude 6.8 Nisqually earthquake occurred on February 28th, 2001 at a depth of about 55 km in the Juan de Fuca slab beneath the southern Puget Sound region of western Washington. The Governor’s Office of the State of Washington estimated damage at more than US$2 billion, making it among the costliest earthquakes in U.S. history.

California, Oregon, Washington↗