PcP phases from a Guatemalan earthquake recorded at Nevada stations of the International seismic network (IM) display evidence of anomalous seismic structure at the core-mantle boundary (CMB); in particular, preand post-cursor phases to PcP and ScP. The data is examined for evidence of an ultra-low velocity zone (ULVZ) by identifying and modeling precursors to PcP. Precursory arrivals to PcP ma...

Laboratory studies on deformation of olivine in response to applied stress suggest two distinct deformation mechanisms in the earth’s upper mantle: diffusion creep through diffusion of atoms along grain boundaries and dislocation creep by slipping along crystallographic glide planes. Each mechanism has very different and important consequences on the dynamical evolution of the mantle and the de...

The surface of Venus is so hot that the lower crust may be weak enough to allow decoupling of mantle and crust. An analytic model of such decoupling assumes that the shallow mande forms the top boundary layers of large scale mantle convection cells. Crustal flow is driven by the motion of the marie and by topographically induced pressure gradients. The model predicts that the lowest lowlands ar...

[1] Much progress has been made over the past several decades in delineating the structure of subducting slabs, but several key aspects of their dynamics remain poorly constrained. Major unsolved problems in subduction geodynamics include those related to mantle wedge viscosity and rheology, slab hydration and dehydration, mechanical coupling between slabs and the ambient mantle, the geometry o...

Spectrum analyses were made of the records of the short-period vertical component of P and PcP phases on seismograms of array stations at Tonto Forest, Arizona, for twenty-one earthquakes over the range A _-47 ø to 83 ø. Generally, as has been reported by other investigators, the trace amplitude ratio of PcP to P is significantly larger than the theoretical ratio. The pulse width of PcP is narr...

The amount of heat flowing from Earth's core critically determines the thermo-chemical evolution of both the core and the lower mantle. Consisting primarily of a polycrystalline aggregate of silicate perovskite and ferropericlase, the thermal boundary layer at the very base of Earth's lower mantle regulates the heat flow from the core, so that the thermal conductivity (k) of these mineral phase...

[1] Convective mixing in the fluid outer core can induce rapid transient decrease of the geomagnetic dipole. Here we determine rates of dipole moment decrease as a function of magnetic Reynolds number following convective instability in a numerical dynamo and in axisymmetric kinematic flows. Our calculations show that mixing flows induce reversed magnetic flux on the core-mantle boundary throug...

The right to search for truth implies also a duty. One must not conceal any part of what one has discovered to be true. O verview The lithosphere clearly controls the location of volcanism. The nature and volume of the volcan-ism and the presence of 'melting anomalies' or 'hotspots,' however, reflect the intrinsic chemical and petrologic heterogeneity of the upper mantle. Melting anomalies-shal...