An ultraviolet-selected galaxy redshift survey: new estimates of the local star formation rate

We present the first results of an ongoing spectroscopic survey of galaxies selected in the rest frame ultraviolet (UV). The source catalogue has been constructed from a flux-limited sample of stars, galaxies and QSOs imaged at 2000 Å in Selected Area 57 with the FOCA balloon-borne imaging camera. Accurate positions for the UV sources have been obtained by matching with optical counterparts using APM scans of the Palomar Sky Survey limited at B   20.5. Here we present results derived from optical spectroscopy conducted with the WIYN telescope and the WHT for 142 faint sources. The redshift distribution for this UV-selected sample extends over 0 <  z  < 0.5, and a high fraction of the sources show intense nebular emission lines and UV–optical colours bluer than normal Hubble sequence galaxies. Such UV-selected surveys are thus a very efficient way to locate and study intermediate-redshift galaxies undergoing intense star formation. Although our sample is currently small, we derive a rest frame UV luminosity function with a steep faint-end slope consistent with that found for late-type galaxies in optical samples. However, the integrated luminosity density derived implies a volume-averaged star formation rate higher than other recent estimates, assuming a normal initial mass function. If representative of other UV fields, as suggested by UV number count studies, our data imply that the local abundance of star-forming galaxies may have been underestimated, and consequently claims for strong evolution in the global star formation rate in the range 0 <  z  < 1 overstated. An intensive study of a large UV-selected sample is likely to reveal important information on the declining population of star-forming galaxies of all types.     

Comparing liquefaction evaluation methods using penetration-VS relationships

Three methods that follow the general format of the Seed-Idriss simplified procedure for evaluating liquefaction resistance of soils are compared in this paper. They are compared by constructing relationships between penetration resistance and small-strain shear–wave velocity (V_S) implied from cyclic resistance ratio (CRR) curves for the three methods, and by plotting penetration-V_S data pairs. The penetration-V_S data pairs are from 43 Holocene-age sand layers in California, South Carolina, Canada, and Japan. It is shown that the V_S-based CRR curve is more conservative than CRR curves based on the Standard Penetration Test (SPT) and Cone Penetration Test (CPT), for the compiled Holocene data. This result agrees with the findings of a recent probability study where the SPT-, CPT-, and V_S-based CRR curves were characterized as curves with average probability of liquefaction of 31, 50, and 26%, respectively. New SPT- and CPT-based CRR equations are proposed that provide more consistent assessments of liquefaction potential for the Holocene sand layers considered.     

Earthquake triggering and delaying caused by fault interaction on Xianshuihe fault belt,southwestern China

The coseismic Coulomb stress change caused by fault interaction and its influences on the triggering and delaying of earthquake are briefly discussed.The Xianshuihe fault belt consists of Luhuo,Daofu,Kangding,Qianning and Ganzi fault.Luohuo(Ms=7.6,1973)-Kangding(Ms=6.2,1975)-Daofu(Ms=6.9,1981)-Ms=6.0,1982)earthquake is a seismic sequence continuous on the time axis with magnitude greater than6.0.They occurred on the Luhuo.Kangding,Daofu and Ganzi fault,respectively.The coseismic Coulomb stress changes caused by each earthquake on its surrounding major faults and microcracks are calculated,and their effects on the triggering and delaying of the next earthquake and aftershocks are analyzed.It is shown that each earthquake of the sequence occurred on the fault segment with coseismic Coulomb stress increases caused by its predecessors,and most after-shocks are distributed along the microcracks with relatively larger coseismic Coulomb stress increases resulted from the main shock.With the fault interaction considered,the seismic potential of each segment along Xianshuihe fault belt is reassessed,and contrasted with those predicted results ignoring coseismic Coulomb stress change,the significance of fault interaction and its effect on triggering and delaying of earthquake are emphasized.It is con-cluded that fault interaction plays a very important role on seismic potential of Xianshuihe fault belt,and the maximal change of future earthquake probability on fault segment is up to 30.5%.     

The UK Large Telescope project

The current status and the organization of the UK Large Telescope programme are summarized. Some scientific and design issues are discussed on the basis of work done for the SERC Large Telescope Panel report. A national Phase A programme is now underway addressing more detailed aspects of these questions. This study will culminate in a final proposal for funding in 1990.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.