San Andreas Fault Earthquake Chronology and Lake Cahuilla History at Coachella, California

The southernmost ~100 km of the San Andreas fault has not ruptured historically. It is imperative to determine its rupture history to better predict its future behavior. This paleoseismic investigation in Coachella, California, establishes a chronology of at least five and up to seven major earthquakes during the past ~1100 yr. This chronology yields a range of average recurrence intervals between 116 and 221 yr, depending on assumptions, with a best-estimate average recurrence interval of 180 yr. The most recent earthquake occurred c.1690, more than 300 yr ago, suggesting that this stretch of the fault has accumulated a large amount of tectonic stress and is likely to rupture in the near future, assuming the fault follows a stress renewal model. This study also establishes the timing of the past 5–6 highstands of ancient Lake Cahuilla since A.D. 800. We found that earthquakes do not tend to occur at any particular stage in the lake cycle

Shock-induced color changes in nontronite: Implications for the Martian fines

Riverside nontronite, a candidate for the major mineral in the Martian fines, becomes both redder and darker upon shock loading between 180 and 300 kbar. The change from olive-yellow (2.5 Y 6/6) to strong brown (7.5 YR 4/6) in the 300-kbar sample brackets the range of color observed at the Viking lander sites. Optical microscopy, X-ray diffraction, optical, infrared, and ^(57)Fe Mössbauer spectroscopy were applied to understand the physical basis of the color change. The Riverside nontronite experienced partial dehydroxylation, probably due to shock-induced heating, that changed the coordination of the Fe3+ in the octahedral layer of the clay to a mixture of 4- and 6-fold or a distorted 5-fold coordination. These changes in the clay cause the O^(2−)-Fe^(3+) charge transfer absorption edge to shift from the near ultraviolet into the visible, producing a redder and darker phase. The absorption spectra of both impacted and nonimpacted Riverside nontronite contains the basic features of the reflectance spectra of the bright regions of Mars: a steep drop in absorption from the near UV into the visible and a featureless near IR region. Calculations indicate that significant impact induced color changes (and dehydration) can occur on Mars, though it seems likely that the mechanism would be more effective, volumetrically, at producing variations in color rather than affecting the absolute color

Ground-Rupturing Earthquakes on the Northern Big Bend of the San Andreas Fault, California, 800 A.D. to Present

Paleoseismic data on the timing of ground-rupturing earthquakes constrain the recurrence behavior of active faults and can provide insight on the rupture history of a fault if earthquakes dated at neighboring sites overlap in age and are considered correlative. This study presents the evidence and ages for 11 earthquakes that occurred along the Big Bend section of the southern San Andreas Fault at the Frazier Mountain paleoseismic site. The most recent earthquake to rupture the site was the Mw7.7–7.9 Fort Tejon earthquake of 1857. We use over 30 trench excavations to document the structural and sedimentological evolution of a small pull-apart basin that has been repeatedly faulted and folded by ground-rupturing earthquakes. A sedimentation rate of 0.4 cm/yr and abundant organic material for radiocarbon dating contribute to a record that is considered complete since 800 A.D. and includes 10 paleoearthquakes. Earthquakes have ruptured this location on average every ~100 years over the last 1200 years, but individual intervals range from ~22 to 186 years. The coefficient of variation of the length of time between earthquakes (0.7) indicates quasiperiodic behavior, similar to other sites along the southern San Andreas Fault. Comparison with the earthquake chronology at neighboring sites along the fault indicates that only one other 1857-size earthquake could have occurred since 1350 A.D., and since 800 A.D., the Big Bend and Mojave sections have ruptured together at most 50% of the time in Mw ≥ 7.3 earthquakes

Late Quaternary slip rates across the central Tien Shan, Kyrgyzstan, central Asia

Slip rates across active faults and folds show that late Quaternary faulting is distributed across the central Tien Shan, not concentrated at its margins. Nearly every intermontane basin contains Neogene and Quaternary syntectonic strata deformed by Holocene north‐south shortening on thrust or reverse faults. In a region that spans two thirds of the north‐south width of the central Tien Shan, slip rates on eight faults in five basins range from ∼0.1 to ∼3 mm/yr. Fault slip rates are derived from faulted and folded river terraces and from trenches. Radiocarbon, optically stimulated luminescence, and thermoluminescence ages limit ages of terraces and aid in their regional correlation. Monte Carlo simulations that sample from normally distributed and discrete probability distributions for each variable in the slip rate calculations generate most likely slip rate values and 95% confidence limits. Faults in basins appear to merge at relatively shallow depths with crustal‐scale ramps that underlie mountain ranges composed of pre‐Cenozoic rocks. The sum and overall pattern of late Quaternary rates of shortening are similar to current rates of north‐south shortening measured using Global Positioning System geodesy. This similarity suggests that deformation is concentrated along major fault zones near range‐basin margins. Such faults, separated by rigid blocks, accommodate most of the shortening in the upper crust

A multiple-methods vertical land movement analysis and its integration into probabilistic sea level rise projections for coastal Washington

In order to support climate change planning and adaptation at the community scale, climate projections should ideally be down-scaled, and also provide meaningful representations of uncertainty. As part of the NOAA-funded Washington Coastal Resilience Project, our team developed new sea level projections for Washington State that feature two innovations. First, the projections include an assessment of the likelihood of occurrence of different sea level magnitudes at decadal intervals through 2150. Next, sea level is projected in a relative framework using vertical land movement information. This presentation will describe the development of the most comprehensive database of vertical land movement observations, along with their uncertainties, ever assembled for coastal Washington State. Vertical land movement observations are derived from multiple sources, including 6 different continuous GPS databases, a single-differencing approach using tide-gauge data, and repeat leveling of survey control monuments near highways. The observations were coupled with a tectonic deformation model of the Cascadia Subduction Zone to develop a best-fit surface for all of coastal Washington, along with its associated uncertainty. The best fit surface and its uncertainty was principally guided by the observations, but in locations with sparse data tectonic deformation model dominated the fit of the surface. The results suggest considerable variability in coastal vertical land movement in coastal Washington State. Rates can vary by \u3e 3 mm/yr over spatial scales of only 10s of kms. Uncertainties also vary, ranging from less then 0.5 mm/yr in places with dense observational data, to \u3e2 mm/yr along parts of the coast of Washington and parts of northern Puget Sound. Using a Monte Carlo approach, vertical land movement estimates and their uncertainties are integrated into probabilistic absolute sea level projections. Then, relative sea level projections are derived at high resolution along Washington\u27s coast. These relative projections are also presented in a probabilistic format, and take into account the uncertainty in sea level projections and the uncertainty in the vertical land movement estimates. The variability in vertical land movement translates into spatial differences in projected relative sea level change of ~0.3 m by 2100. Coastal locations in Washington State with the highest rates of uplift are assessed to have, as a best estimate (i.e. median projection), a relative sea level by 2100 of ~0.4 m relative to contemporary sea level. By contrast the best estimate of relative sea level 2100 at locations with land subsidence may exceed ~0.7 m relative to contemporary sea level

20th to 21st Century Relative Sea and Land Level Changes in Northern California: Tectonic Land Level Changes and their Contribution to Sea-Level Rise, Humboldt Bay Region, Northern California

Sea-level changes are modulated in coastal northern California by land-level changes due to the earthquake cycle along the Cascadia subduction zone, the San Andreas plate boundary fault system, and crustal faults. Sea-level rise (SLR) subjects ecological and anthropogenic infrastructure to increased vulnerability to changes in habitat and increased risk for physical damage. The degree to which each of these forcing factors drives this modulation is poorly resolved. We use NOAA tide gage data and ‘campaign’ tide gage deployments, Global Navigation Satellite System (GNSS) data, and National Geodetic Survey (NGS) first-order levelling data to calculate vertical land motion (VLM) rates in coastal northern California. Sea-level observations, highway level surveys, and GNSS data all confirm that land is subsiding in Humboldt Bay, in contrast to Crescent City where the land is rising. Subtracting absolute sea-level rate (~1.99 mm/year) from Crescent City (CC) and North Spit (NS) gage relative sea-level rates reveals that CC is uplifting at ~2.83 mm/year and NS is subsiding at ~3.21mm/year. GNSS vertical deformation reveals similar rates of ~2.60 mm/year of uplift at Crescent City. In coastal northern California, there is an E-W trending variation in vertical land motion that is primarily due to Cascadia megathrust fault seismogenic coupling. This interseismic subsidence also dominates the N-S variation in vertical land motion in most of the study region. There exists a second-order heterogeneous N-S trend in vertical land motion that we associate to crustal fault-related strain. There may be non-tectonic contributions to the observed VLM rates

Heavy lepton pair production in nucleus-nucleus collisions at LHC energy - a case study

We present a study of $\tau^{+}\tau^{-}$ lepton pair production in Pb+Pb collisions at $\sqrt{s_{NN}}$ = 5.5 TeV. The larger $\tau^{\pm}$ mass ($\sim$ 1.77 GeV) compared to $e^{\pm}$ and $\mu^{\pm}$ leads to considerably small hadronic contribution to the $\tau^{+}\tau^{-}$ pair invariant mass ($M$) distribution relative to the production from thermal partonic sources. The quark-anti-quark annihilation processes via intermediary virtual photon, Z and Higgs bosons have been considered for the production of $\tau^{+}\tau^{-}$. We observe that the contribution from Drell-Yan process dominates over thermal yield for $\tau^{+}\tau^{-}$ pair mass from 4 to 20 GeV at the LHC energy. We also present the ratio of $\tau$ lepton pair yields for nucleus-nucleus collisions relative to yields from p+p collisions scaled by number of binary collisions at LHC energies as a function $\tau$ pair mass. The ratio is found to be significantly above unity for the mass range 4 to 6 GeV. This indicates the possibility of detecting $\tau^{+}\tau^{-}$ pair from quark gluon plasma (QGP) in the mass window $4\leq M$(GeV)$\leq 6$.Comment: Five pages with one LaTeX file and three eps files for figure

Long-Term Time-Dependent Probabilities for the Third Uniform California Earthquake Rupture Forecast (UCERF3)

The 2014 Working Group on California Earthquake Probabilities (WGCEP 2014) presents time-dependent earthquake probabilities for the third Uniform California Earthquake Rupture Forecast (UCERF3). Building on the UCERF3 time-independent model published previously, renewal models are utilized to represent elastic-rebound-implied probabilities. A new methodology has been developed that solves applicability issues in the previous approach for unsegmented models. The new methodology also supports magnitude-dependent aperiodicity and accounts for the historic open interval on faults that lack a date-of-last-event constraint. Epistemic uncertainties are represented with a logic tree, producing 5760 different forecasts. Results for a variety of evaluation metrics are presented, including logic-tree sensitivity analyses and comparisons to the previous model (UCERF2). For 30 yr M ≥ 6.7 probabilities, the most significant changes from UCERF2 are a threefold increase on the Calaveras fault and a threefold decrease on the San Jacinto fault. Such changes are due mostly to differences in the time-independent models (e.g., fault-slip rates), with relaxation of segmentation and inclusion of multifault ruptures being particularly influential. In fact, some UCERF2 faults were simply too long to produce M 6.7 size events given the segmentation assumptions in that study. Probability model differences are also influential, with the implied gains (relative to a Poisson model) being generally higher in UCERF3. Accounting for the historic open interval is one reason. Another is an effective 27% increase in the total elastic-rebound-model weight. The exact factors influencing differences between UCERF2 and UCERF3, as well as the relative importance of logic-tree branches, vary throughout the region and depend on the evaluation metric of interest. For example, M ≥ 6.7 probabilities may not be a good proxy for other hazard or loss measures. This sensitivity, coupled with the approximate nature of the model and known limitations, means the applicability of UCERF3 should be evaluated on a case-by-case basis