Before London

The idea that London had pre-Roman origins is considered, but dismissed for the want of evidence from both within and around the city. The pre-settlement landscape and topography of the region is described, tracing the course and character of the Thames and London’s other rivers including the lost Walbrook. The pre-history of the London basin is summarized, and London’s place in the emerging political landscape of late Iron Age Britain reviewed. It is concluded that the area where Roman London was established lay on the border of earlier polities and that the Thames constituted a boundary zone and relative backwater. The sites of pre-Roman farmsteads within this landscape are identified and described, including important settlements at Bermondsey and Southwark that may have been occupied at the time of the Roman conquest. It is speculated that London gained its Roman name and identity from these pre-Roman farmsteads on the south bank of the river, making it a place of Kent. The city itself was a Roman creation, made possible by the political unification of southern Britain through the force of conquest.

Reflection of sound pulses from an inhomogeneous bubble medium

The effect of changes in the volume concentration of bubbles in the boundary zone of the bubble medium on the nature of reflection and radiation of the excited bubble medium is studied. The spectral characteristics of the radiation of a bubble medium are obtained at the initial stage of transition radiation and at large times when the radiation is stationary. It is shown that in the initial phase the emission spectrum is broadband and is located in the absorption band of the bubble medium, and at large times the emission spectrum is located outside this band.

Source Properties of Moderate-Magnitude Earthquakes Along the Alpine Fault, New Zealand

<p><b>The Alpine Fault is a major active continental transform fault that is late in its typical cycle of large earthquakes. Extensive paleoseismic research has revealed that the central segment of the Alpine Fault ruptures in M7+ earthquakes every 291±23 years and last ruptured in 1717 AD. The paleoseismic results also reveal that some places along the fault, which coincide with pronounced along-strike changes in fault characteristics, act as conditional barriers to rupture. The geometry, seismicity rates and geology of the Alpine Fault change along three principal segments (North Westland, Central and South Westland segments) but it is unclear whether source properties (e.g. stress drop) of near-fault seismicity also vary between those fault segments, and whether these properties have some influence on conditional segmentation of the Alpine Faultduring large earthquake rupture.</b></p> <p>To examine whether source properties of earthquakes can influence or elucidate the conditional segmentation of Alpine Fault earthquakes, we have computed stress drops of moderate-magnitude earthquakes occurring on and close to the Alpine Fault. We use an empirical Green’s function (EGF) approach and require each EGF earthquake to be highly correlated (cross-correlation ≥0.8) with its respective mainshock. We use data from dense, temporary seismometer networks, including DWARFS (Dense WestlandArrays Researching Fault Segmentation), a new two-part network designed to constrain seismogenic behaviour near key transitional boundaries. Our results investigate the spatial variability of these source properties along the length of the Alpine Fault, focusing on whether earthquakes at the rupture segment boundaries behave differently to those in the middle of previously identified rupture segments.</p> <p>We analyse individual P- and S-wave measurements of corner frequency and stress drop for 95 earthquakes close to (within 5 km) and on the Alpine Fault. Overall, the calculated stress drops range between 1–352 MPa and show good agreement with other studies both within New Zealand and worldwide. The stress drop values obtained for the three Alpine segment are: 1–143 MPa (median values of 8 and 9 MPa for P- and S-waves, respectively) for the South Westland/Central segment boundary zone, 2–309 MPa (median values of 17 and 39 MPa for P- and S-waves, respectively) for the Central segment and 1–352 MPa (median values of 15 and 19 MPa for P- and S-waves, respectively) for the North Westland/Central segment boundary zone. There are no marked differences in stress drop values along the North Westland and Central segments, but those values are slightly higher than along the South Westland segment.</p> <p>This may indicate a bigger difference in fault geometry, slip and seismicity rate compare with other segments, or that the South Westland segment is weaker than the other segments. We see no clear dependence of stress drop values on depth, magnitude or focal mechanism.</p>

Source Properties of Moderate-Magnitude Earthquakes Along the Alpine Fault, New Zealand

<p><b>The Alpine Fault is a major active continental transform fault that is late in its typical cycle of large earthquakes. Extensive paleoseismic research has revealed that the central segment of the Alpine Fault ruptures in M7+ earthquakes every 291±23 years and last ruptured in 1717 AD. The paleoseismic results also reveal that some places along the fault, which coincide with pronounced along-strike changes in fault characteristics, act as conditional barriers to rupture. The geometry, seismicity rates and geology of the Alpine Fault change along three principal segments (North Westland, Central and South Westland segments) but it is unclear whether source properties (e.g. stress drop) of near-fault seismicity also vary between those fault segments, and whether these properties have some influence on conditional segmentation of the Alpine Faultduring large earthquake rupture.</b></p> <p>To examine whether source properties of earthquakes can influence or elucidate the conditional segmentation of Alpine Fault earthquakes, we have computed stress drops of moderate-magnitude earthquakes occurring on and close to the Alpine Fault. We use an empirical Green’s function (EGF) approach and require each EGF earthquake to be highly correlated (cross-correlation ≥0.8) with its respective mainshock. We use data from dense, temporary seismometer networks, including DWARFS (Dense WestlandArrays Researching Fault Segmentation), a new two-part network designed to constrain seismogenic behaviour near key transitional boundaries. Our results investigate the spatial variability of these source properties along the length of the Alpine Fault, focusing on whether earthquakes at the rupture segment boundaries behave differently to those in the middle of previously identified rupture segments.</p> <p>We analyse individual P- and S-wave measurements of corner frequency and stress drop for 95 earthquakes close to (within 5 km) and on the Alpine Fault. Overall, the calculated stress drops range between 1–352 MPa and show good agreement with other studies both within New Zealand and worldwide. The stress drop values obtained for the three Alpine segment are: 1–143 MPa (median values of 8 and 9 MPa for P- and S-waves, respectively) for the South Westland/Central segment boundary zone, 2–309 MPa (median values of 17 and 39 MPa for P- and S-waves, respectively) for the Central segment and 1–352 MPa (median values of 15 and 19 MPa for P- and S-waves, respectively) for the North Westland/Central segment boundary zone. There are no marked differences in stress drop values along the North Westland and Central segments, but those values are slightly higher than along the South Westland segment.</p> <p>This may indicate a bigger difference in fault geometry, slip and seismicity rate compare with other segments, or that the South Westland segment is weaker than the other segments. We see no clear dependence of stress drop values on depth, magnitude or focal mechanism.</p>

Supplemental Material: Late Cenozoic tephrochronology of the Mount Diablo area within the evolving plate-tectonic boundary zone of northern California

Terminology relating to tephra and tephra layer nomenclature, methods of sampling tephra in the field, laboratory treatment of tephra samples for analysis, methods of chemical analysis of tephra and radiometric dating (40Ar/39Ar), and methods of data evaluation<br>

Supplemental Material: Late Cenozoic tephrochronology of the Mount Diablo area within the evolving plate-tectonic boundary zone of northern California

Terminology relating to tephra and tephra layer nomenclature, methods of sampling tephra in the field, laboratory treatment of tephra samples for analysis, methods of chemical analysis of tephra and radiometric dating (40Ar/39Ar), and methods of data evaluation<br>

Supplemental Material: Late Cenozoic tephrochronology of the Mount Diablo area within the evolving plate-tectonic boundary zone of northern California

Terminology relating to tephra and tephra layer nomenclature, methods of sampling tephra in the field, laboratory treatment of tephra samples for analysis, methods of chemical analysis of tephra and radiometric dating (40Ar/39Ar), and methods of data evaluation<br>

Characterization of a Bimetallic Multilayered Composite “Stainless Steel/Copper” Fabricated with Wire-Feed Electron Beam Additive Manufacturing

The results of investigating the structure and properties of multilayered bimetallic “steel–copper” macrocomposite systems, obtained by wire-feed electron beam additive manufacturing, are presented in the paper. The features of boundary formation during 3D printing are revealed when changing the filaments of stainless steel and copper. Inhomogeneities in the distribution of steel and copper in the boundary zone were detected. Interphase interaction occurs both in the steel and copper parts of the structural boundary: Cu particles with an average size of 5 µm are formed in the iron matrix; Fe particles with an average size of 10 µm are formed in the copper matrix. It was revealed that such structural elements, as solid solutions of both copper and iron, are formed in the boundary zone, with additional mutual dissolution of alloying elements and mechanical mixtures of system components. The presence of the disc-shaped precipitations randomly located in the matrix was revealed in the structure of the “copper–steel” boundary by transmission electron microscopy; this is associated with rapid cooling of alloys and the subsequent thermal effect at lower temperatures during the application of subsequent layers. The existence of these disc-shaped precipitations of steel, arranged randomly in the Cu matrix, allows us to draw conclusions on the spinodal decomposition of alloying elements of steel. The characteristics of mechanical and micromechanical properties of a bimetallic multilayered composite with a complex formed structure lie in the range of characteristics inherent in additive steel and additive copper.