Extreme multi-millennial slip rate variations on the Garlock fault, California: Strain super-cycles, potentially time-variable fault strength, and implications for system-level earthquake occurrence

Pronounced variations in fault slip rate revealed by new measurements along the Garlock fault have basic implications for understanding how faults store and release strain energy in large earthquakes. Specifically, dating of a series of 26.0+3.5/−2.5 m fault offsets with a newly developed infrared-stimulated luminescence method shows that the fault was slipping at >14.0+2.2/−1.8 mm/yr, approximately twice as fast as the long-term average rate, during a previously documented cluster of four earthquakes 0.5–2.0 ka. This elevated late Holocene rate must be balanced by periods of slow or no slip such as that during the ca. 3300-yr-long seismic lull preceding the cluster. Moreover, whereas a comparison of paleoseismic data and stress modeling results suggests that individual Garlock earthquakes may be triggered by periods of rapid San Andreas fault slip or very large-slip events, the “on–off” behavior of the Garlock suggests a longer-term mechanism that may involve changes in the rate of elastic strain accumulation on the fault over millennial time scales. This inference is consistent with most models of the geodetic velocity field, which yield slip-deficit rates that are much slower than the average latest Pleistocene-early Holocene (post-8–13 ka) Garlock slip rate of 6.5±1.5 mm/yr. These observations indicate the occurrence of millennia-long strain “super-cycles” on the Garlock fault that may be associated with temporal changes in elastic strain accumulation rate, which may in turn be controlled by variations in relative strength of the various faults in the Garlock-San Andreas-Eastern California Shear Zone fault system and/or changes in relative plate motion rates

Paleoseismology of the southern Panamint Valley fault: Implications for regional earthquake occurrence and seismic hazard in southern California

Paleoseismologic data from the southern Panamint Valley fault (PVF) reveal evidence of at least four surface ruptures during late Holocene time (0.33-0.48 ka, 0.9-3.0 ka, 3.3-3.6 ka, and >4.1 ka). These paleo-earthquake ages indicate that the southern PVF has ruptured at least once and possibly twice during the ongoing (≤1.5 ka) seismic cluster in the Mojave section of the eastern California shear zone (ECSZ). The most recent event (MRE) on the PVF is also similar in age to the 1872 Owens Valley earthquake and the geomorphically youthful MRE on the Death Valley fault. The timing of the three oldest events at our site shows that the PVF ruptured at least once and possibly thrice during the well-defined 2-5 ka seismic lull in the Mojave section of the ECSZ. Interestingly, the 3.3-3.6 ka age of Event 3 overlaps with the 3.3-3.8 ka age of the penultimate (i.e., pre-1872) rupture on the central Owens Valley fault. These new PVF data support the notion that earthquake occurrence in the ECSZ may be spatially and temporally complex, with earthquake clusters occurring in different regions at different times. Coulomb failure function modeling of the Panamint Valley and Garlock faults reveals significant stress interactions between these two faults that may influence future earthquake occurrence. Specifically, our models suggest a possible rupture sequence whereby an event on the southern Panamint Valley fault can lead to the potential triggering of an event on the Garlock fault, which in turn could trigger the Mojave section of the San Andreas Fault. Key Points Four surface ruptures during late Holocene on the Panamint Valley faultData support notion that earthquake occurrences in the ECSZ are complexCFF modeling of the Garlock and Panamint Valley fault

Deriving the dietary approaches to stop hypertension (DASH) score in women from seven pregnancy cohorts from the European alphabet consortium

The ALPHABET consortium aims to examine the interplays between maternal diet quality, epigenetics and offspring health in seven pregnancy/birth cohorts from five European countries. We aimed to use the Dietary Approaches to Stop Hypertension (DASH) score to assess diet quality, but different versions have been published. To derive a single DASH score allowing cross-country, cross-cohort and cross-period comparison and limiting data heterogeneity within the ALPHABET consortium, we harmonised food frequency questionnaire (FFQ) data collected before and during pregnancy in ≥26,500 women. Although FFQs differed strongly in length and content, we derived a consortium DASH score composed of eight food components by combining the prescriptive original DASH and the DASH described by Fung et al. Statistical issues tied to the nature of the FFQs led us to re-classify two food groups (grains and dairy products). Most DASH food components exhibited pronounced between-cohort variability, including non-full-fat dairy products (median intake ranging from 0.1 to 2.2 servings/day), sugar-sweetened beverages/sweets/added sugars (0.3–1.7 servings/day), fruits (1.1–3.1 servings/day), and vegetables (1.5–3.6 servings/day). We successfully developed a harmonized DASH score adapted to all cohorts being part of the ALPHABET consortium. This methodological work may benefit other research teams in adapting the DASH to their study’s specificities

Assessing uncertainties in crop and pasture ensemble model simulations of productivity and N2O emissions

Simulation models are extensively used to predict agricultural productivity and greenhouse gas emissions. However, the uncertainties of (reduced) model ensemble simulations have not been assessed systematically for variables affecting food security and climate change mitigation, within multi‐species agricultural contexts. We report an international model comparison and benchmarking exercise, showing the potential of multi‐model ensembles to predict productivity and nitrous oxide (N2O) emissions for wheat, maize, rice and temperate grasslands. Using a multi‐stage modelling protocol, from blind simulations (stage 1) to partial (stages 2–4) and full calibration (stage 5), 24 process‐based biogeochemical models were assessed individually or as an ensemble against long‐term experimental data from four temperate grassland and five arable crop rotation sites spanning four continents. Comparisons were performed by reference to the experimental uncertainties of observed yields and N2O emissions. Results showed that across sites and crop/grassland types, 23%–40% of the uncalibrated individual models were within two standard deviations (SD) of observed yields, while 42 (rice) to 96% (grasslands) of the models were within 1 SD of observed N2O emissions. At stage 1, ensembles formed by the three lowest prediction model errors predicted both yields and N2O emissions within experimental uncertainties for 44% and 33% of the crop and grassland growth cycles, respectively. Partial model calibration (stages 2–4) markedly reduced prediction errors of the full model ensemble E‐median for crop grain yields (from 36% at stage 1 down to 4% on average) and grassland productivity (from 44% to 27%) and to a lesser and more variable extent for N2O emissions. Yield‐scaled N2O emissions (N2O emissions divided by crop yields) were ranked accurately by three‐model ensembles across crop species and field sites. The potential of using process‐based model ensembles to predict jointly productivity and N2O emissions at field scale is discussed

Spatial structure in lotic macroinvertebrate communities in England and Wales: relationship with physicochemical and anthropogenic stress variables

We describe the relationship between macroinvertebrate community composition, the physicochemical environment and anthropogenic impacts, in running water sites across a range of water qualities in England and Wales. We have also investigated the degree of spatial structure present in both the macroinvertebrate community and the measured environment. Selected explanatory variables could account for 26% of the variation in lotic macroinvertebrate assemblage composition across England and Wales. The explanatory power of the CCA model was based predominantly on a combination of local scale variables (substrate, alkalinity, urban run-off) and regional scale variables (discharge category, northing). The physicochemical gradient associated with changes in stream type from headwaters to estuary dominated assemblage composition. The influence of pollution and habitat modification were of secondary importance. There was a substantial level of spatial structure to both the physicochemical (47% of its explanatory power spatially structured) and anthropogenic stress data (63% of its explanatory power spatially structured), which resulted in a high level of predictable spatial structuring in macroinvertebrate assemblages. Almost 40% of the variation in assemblage composition accounted for by the explanatory model exhibited spatial structure. Positive spatial autocorrelation in macroinvertebrate community composition extended to sites up to 150 km apart. As a consequence, community composition could be described from northing and easting with 75% of the explanatory power of the eight physicochemical variables. Our study has confirmed the importance of the longitudinal gradient within catchments, as well as the geographical position of the catchment to macroinvertebrate communities. We have also demonstrated how quantifying the spatial structure in the dataset can improve our understanding of the factors influencing macroinvertebrate community structure

Measuring medium-term sheet erosion in gullies from trees: A case study using dendrogeomorphological analysis of exposed pine roots in central Iberia

The assessment of gully erosion poses a great challenge because of the complexity and connectivity of the geomorphic processes involved. This study focuses on the quantification of sheet erosion rates in a set of slope gullies located on the northern piedmont of the Guadarrama Mountains (Spanish Central System). In order to delineate accurately the gully areas in which sheet erosion was predominant, the Hydrologic/Erosion Response Unit (HRU/ERU) approach was used and a dendrogeomorphological analysis of exposed tree roots was carried out to quantify sheet erosion rates in one selected HRU/ERU. Identification of the first year of exposure by erosion from anatomical criteria was therefore critical. The 29 samples taken were prepared for anatomical analysis and cross-dated. Anatomical analysis of the samples showed a reduction in the lumen area of earlywood tracheids following root exposure and also, in most cases, a slight increase in growth rings. Moreover, at the end of the ring, latewood tissue and visible annual borders were very clearly defined by several rows of thick-walled tracheids. A non-parametric test was used on the findings derived from this qualitative analysis to objectify determination of the first year of exposure. Estimates of sheet erosion were obtained by dividing the height of eroded soil by the number of years that each root was exposed. The mean value of soil erosion for the entire study site was then determined from statistical inference. Using this procedure, a range of sheet erosion rates between 6.2 and 8.8 mm y−1 (125.2 and 177.8 t ha−1 year−1) was obtained for the dominant HRU/ERU of these gullies in central Iberia. These estimates of eroded soil thickness were adjusted based on the recent finding that root anatomical changes occur prior to their exposure by erosion