Unified algebraic treatment of resonance

Energy resonance in scattering is usually investigated either directly in the complex energy plane (E-plane) or indirectly in the complex angular momentum plane (L-plane). Another formulation complementing these two approaches was introduced recently. It is an indirect algebraic method that studies resonances in a complex charge plane (Z-plane). This latter approach will be generalized to provide a unified algebraic treatment of resonances in the complex E-, L-, and Z-planes. The complex scaling (rotation) method will be used in the development of this approach. The resolvent operators (Green's functions) are formally defined in these three spaces. Bound states spectrum and resonance energies in the E-plane are mapped onto a discrete set of poles of the respective resolvent operator on the real line of the L- and Z-planes. These poles move along trajectories as the energy is varied. A finite square integrable basis is used in the numerical implementation of this approach. Stability of poles and trajectories against variation in all computational parameters is demonstrated. Resonance energies for a given potential are calculated and compared with those obtained by other studies.Comment: 15 pages, 1 Table, 7 Figures (6 are snapshots of videos

The ISC-GEM Earthquake Catalogue (1904–2014): status after the Extension Project

We outline the work done to extend and improve the ISC-GEM Global Instrumental Earthquake Catalogue, a dataset which was first released in 2013 (Storchak et al., 2013, 2015). In its first version (V1) the catalogue included global earthquakes selected according to time-dependent cut-off magnitudes: 7.5 and above between 1900 and 1918 (plus significant continental earthquakes 6.5 and above); 6.25 between 1918 and 1959; 5.5 between 1960 and 2009. Such selection criteria were dictated by time and resource limitations. With the Extension Project we added both pre-1960 events below the original cut-off magnitudes (if enough station data were available to perform relocation and magnitude recomputation) and added events with magnitude 5.5 and above from 2010 to 2014. The project ran over a 4-year period during which a new version of the ISC-GEM Catalogue was released each year via the ISC website (http://http://www.isc.ac.uk/iscgem/, last access: 10 October 2018). For each year, not only have we added new events to the catalogue for a given time range but also revised events already in V1 if additional data became available or location and/or magnitude reassessments were required. Here we recall the general background behind the production of the ISC-GEM Catalogue and describe the features of the different periods in which the catalogue has been extended. Compared to the 2013 release, we eliminated earthquakes during the first 4 years (1900–1903) of the catalogue (due to lack of reliable station data), added approximately 12&thinsp;000 and 2500 earthquakes before 1960 and between 2010 and 2014, respectively, and improved the solution for approximately 2000 earthquakes already listed in previous versions. We expect the ISC-GEM Catalogue to continue to be one of the most useful datasets for studies of the Earth's global seismicity and an important benchmark for seismic hazard analyses, and, ultimately, an asset for the seismological community as well as other geoscience fields, education and outreach activities. The ISC-GEM Catalogue is freely available at https://doi.org/10.31905/D808B825.</p

Direct inversion of S-P differential arrival-times for Vp/Vs ratio in SE Asia

Open Access via Jisc Wiley agreementPeer reviewedPublisher PD

Magnetostrictive and magnetoelectric behavior of Fe–20 at. % Ga/Pb(Zr,Ti)O3 laminates

The magnetostrictive and magnetoelectric (ME) properties of laminate composites of Fe–20 at. % Ga and Pb(Zr,Ti)O3 (PZT) have been studied for laminates of different geometries. The results show that (i) a long-type magnetostrictive Fe–20 at. % Ga crystal plate oriented along 〈001〉c and magnetized in its longitudinal (or length) direction has higher magnetostriction than a disk-type one; and consequently (ii) a long-type Fe–20 at. % Ga/PZT laminate has a giant ME effect, and is sensitive to low-level magnetic fields

Fe–Ga/Pb(Mg1/3Nb2/3)O3–PbTiO3 magnetoelectric laminate composites

We have found large magnetoelectric (ME) effects in long-type laminate composites of Fe–20%Ga magnetostrictive alloys and piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals. At lower frequencies, the ME voltage coefficient of a laminate with longitudinally magnetized and longitudinally polarized (i.e., L-L mode) layers was 1.41 V/Oe (or1.01 V/cm Oe). Near the natural resonant frequency ( ∼ 91 kHz) of the laminate, the ME voltage coefficients were found to be dramatically increased to 50.7 V/Oe (36.2 V/cm Oe)for the L-L mode. In addition, the laminate can detect a minute magnetic field as low as ∼ 2×10−12 T at resonance frequency, and ∼ 1×10−10 T at lower frequencies

Crustal structure of the Kermadec arc from MANGO seismic refraction profiles

Three active-source seismic refraction profiles are integrated with morphological and potential field data to place the first regional constraints on the structure of the Kermadec subduction zone. These observations are used to test contrasting tectonic models for an along-strike transition in margin structure previously known as the 32°S boundary. We use residual bathymetry to constrain the geometry of this boundary and propose the name Central Kermadec Discontinuity (CKD). North of the CKD, the buried Tonga Ridge occupies the forearc with VP 6.5–7.3 km s-1 and residual free-air gravity anomalies constrain its latitudinal extent (north of 30.5°S), width (110 ± 20 km) and strike (~005° south of 25°S). South of the CKD the forearc is structurally homogeneous down-dip with VP 5.7–7.3 km s-1. In the Havre Trough backarc, crustal thickness south of the CKD is 8-9 km, which is up-to 4 km thinner than the northern Havre Trough and at least 1 km thinner than the southern Havre Trough. We suggest that the Eocene arc did not extend along the current length of the Tonga-Kermadec trench. The Eocene arc was originally connected to the Three Kings Ridge and the CKD was likely formed during separation and easterly translation of an Eocene arc substrate during the early Oligocene. We suggest that the first-order crustal thickness variations along the Kermadec arc were inherited from before the Neogene and reflect Mesozoic crustal structure, the Cenozoic evolution of the Tonga-Kermadec-Hikurangi margin and along-strike variations in the duration of arc volcanism

Comparing P and S wave heterogeneity in the mantle

From the reprocessed data set of Engdahl and co-workers we have carefully selected matching P and S data for tomographic imaging. We assess data and model error and conclude that our S model uncertainty is twice that of the P model. We account for this in our comparison of the perturbations in P and S-wavespeed. In accord with previous studies we find that P and S perturbations are positively correlated at all depths. However, in the deep mantle systematic di fferences occur between regions that have undergone subduction in the last 120 million years and those that have not. In particular, below 1500 km depth ∂ ln Vs/∂ ln Vp is signifi cantly larger in mantle regions away from subduction than in mantle beneath convergent margins. This inference is substantiated by wavespeed analyses with random realizations of the slab/non-slab distribution. Through much of the mantle there is no signi ficant correlation between bulk sound and S-wave perturbations, but they appear to be negatively correlated between 1700 and 2100 km depth, which is also where the largest di erences in ∂ ln Vs/∂ ln Vp occur. This finding supports convection models with compositional heterogeneity in the lowermost mantle

Upper- and mid-mantle interaction between the Samoan plume and the Tonga-Kermadec slabs

Mantle plumes are thought to play a key role in transferring heat from the core\u2013mantle boundary to the lithosphere, where it can significantly influence plate tectonics. On impinging on the lithosphere at spreading ridges or in intra-plate settings, mantle plumes may generate hotspots, large igneous provinces and hence considerable dynamic topography. However, the active role of mantle plumes on subducting slabs remains poorly understood. Here we show that the stagnation at 660 km and fastest trench retreat of the Tonga slab in Southwestern Pacific are consistent with an interaction with the Samoan plume and the Hikurangi plateau. Our findings are based on comparisons between 3D anisotropic tomography images and 3D petrological-thermo-mechanical models, which self-consistently explain several unique features of the Fiji\u2013Tonga region. We identify four possible slip systems of bridgmanite in the lower mantle that reconcile the observed seismic anisotropy beneath the Tonga slab (VSH4VSV) with thermo-mechanical calculations