Raymond Willemann

IRIS Consortium

During July 2011, a Pan-American Advanced Studies Institute, "New Frontiers in Seismological Research: Sustainable Networks, Earthquake Source Parameters, and Earth Structure" was conducted in Quito Ecuador with participants from the US, Central, and South America, and the Caribbean at early stages in their scientific careers. This advanced studies...

At some point, President Obama may ask the Senate to vote on ratification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Despite continuing advances in seismological monitoring methods, CTBT opponents continue to assert—in opinion columns in the Wall Street Journal and elsewhere— that there are significant doubts about “verifiability.” To con...

Openly exchanged seismological data contribute to research and monitoring related to the CTBT and complement the more formally structured and restricted data procedures of the International Monitoring System (IMS). In addition to providing an increasingly rich source of data for fundamental research programs and monitoring, the open exchange of dat...

Building a sustainable earthquake monitoring system requires well-informed cooperation between commercial companies that manufacture components or deliver complete systems and the government or other agencies that will be responsible for operating them. Many nations or regions with significant earthquake hazard lack the financial, technical, and hu...

Over the past quarter century, national investments in high-fidelity digital seismograph networks have resulted in a global infrastructure for real-time in situ earthquake monitoring. Many network operators adhere to community-developed standards, with the result that there are few technical impediments to data sharing and real-time information exc...

Is there a “right” model for global, regional and local earthquake monitoring? It's timely to ask that question because of a convergence of events and trends: the 2004 tsunami and the calls for enhanced early warning systems based on national and regional seismological networks, the growingstrength of a private sector marketing turn-key solutions f...

Geophysical networks are defined not only by their technical specifications, but also by the characteristics and needs of the communities that use them. Growing populations supported by more elaborate urban infrastructure with its fine-grained socio-economic interdependencies and relying on global and regional connections for sustainability make ne...

The flow of the mantle near subducted lithosphere applies a force (dynamic load) to the slab which has a normal component as well as a shear component. In addition, the greater density of the slab compared to the surrounding mantle results in a downward force (negative buoyancy) which also has a component normal to the slab. Because the slab is lon...

This paper demonstrates that well-known methods of cluster analysis and multivariate data analysis are useful for geodynamic interpretation of seismic moment tensors. To use these methods, moment tensors are expressed as vectors in a 6-D space. These are vectors in a rigorous sense, rather than an arbitrary set of ordered numbers, because a dot pro...

Installing or upgrading a seismic monitoring network is often among the mitigation efforts after earthquake disasters, and this is happening in response to the events both in Sumatra during December 2004 and in Pakistan during October 2005. These networks can yield improved hazard assessment, more resilient buildings where they are most needed, and...

For many types seismological studies, after selecting appropriate events the next step is to retrieve waveforms. Some data centres assemble sets of waveform segments for a few events of particular interest. Links to such set are included in the ISC On-line Bulletin. In addition, the ISC web site now includes a system for extracting data from multip...

Statistical methods for comparing travel time residuals are reviewed and the importance of using a statistic that is both robust and a measure of dispersion is demonstrated. Results from relocations based on travel times from the Jeffreys-Bullen (JB) tables and from a tomographic (3D) model are compared using the variance of the Winsorized samples,...

The International Seismological Centre is replacing the software it uses to calculate hypocentres, which it does using arrival times from all over the world. The new program will initialy use the same algorithms as now but can also be used to test ways of improving solutions using modern methods. Here, we investigate using travel times from three d...

For earthquakes from 2001 January and on, the ISC is using local, regional and teleseismic S arrival times to compute hypocenters in addition to the local, regional and teleseismic P that it has always used. S times are used with one half the weight of P times to allow for the greater variance of reported S arrival times. The hypocenters are comput...

NOAA's Pacific Marine Environment Laboratory (PMEL) produces a catalogue of Pacific Ocean earthquakes based on hydroacoustic monitoring from April 1996. The International Seismological Centre (ISC) worked without referring to the PMEL catalogue for earthquakes through April 2000, so the ISC and PMEL catalogues are independent until then. The PMEL c...

Readings from well over 2000 seismic stations each year help to ensure reliability of the ISC Bulletin, but the density of reporting stations varies widely. It can be hard to distinguish between true changes in seismicity and artifacts from changes among reporting stations, especially without magnitude for some events. The capability can be charact...

To prepare to update location procedures at the International Seismo-logical Centre (ISC), we conduct a global test of location accuracy using two 3D Earth models and three 1D models (Jeffreys-Bullens [J-B], Preliminary Reference Earth Model [PREM], ak135) with initial phase arrival times from different distance ranges. The 3D models include one sp...

Readings from well over 2000 seismic stations each year help to ensure reliability of the Bulletin of the International Seismological Centre (ISC). But the density of re- porting stations varies widely around the world, partly because the ISC aims to be comprehensive rather than uniform. The effect of station density is important but dif- ficult to...

The ISC Bulletin for year 1999 is now available on the Internet and the ISC CD Vol- ume 10. In our presentation, we will give an overview of the data published in the Bulletin. We describe the major sources of data contributed to the ISC, including arrival times and amplitude readings and compare the data sets from other major data centres with tha...

Many seismological agencies are considering new algorithms and travel time models to compute more accurate hypocenters and uncertainties. It is preferable to evaluate alternative hypocenters by comparison with reference locations for very well located events. But reference locations remain sparse in some regions, so a supplementary approach to eval...

In support of the proposed Comprehensive Nuclear Test Ban Treaty, a large database of hydrophone recordings including T?phases, explosions, and noise has been compiled and cross referenced with known seismic events at the Center for Monitoring Research. Using this database, an automated hydroacoustic arrival detection and classification system has...

The rolling text of Conference on Disarmament?s Nuclear Test Ban Treaty requires monitoring by 169 seismic, 11 hydroacoustic, 60 infrasonic, and 50 radionuclide stations. Stations will continuously transmit data to a center for real?time processing. Processing will detect, measure, and classify signals, then it will associate signals at different s...

A stress diffusion model is adapted for application to subducted lithosphere by including a gravitational body force parallel to the direction of diffusion. In the model a sequence of step function boundary displacements represents a history of interplate thrust earthquakes. The response of subducted lithosphere to these displacements is approximat...

In a model for the depth distribution of deep earthquakes, I assume that deep earthquakes occur only above a critical deviatoric stress and that where the stress is achieved the seismicity rate is proportional to the strain rate. The model seismicity rate increases sharply before terminating, in agreement with the observed depth distribution. Since...

Some earthquakes with focal depths exceeding 70 km possess one or more aftershocks which are well recorded by stations at teleseis-mic distances. Precise determination of relative vectors separating the aftershocks and ~ 60 initial events finds the vector directions are distributed uniformly with respect to the nodal plane of main shock focal mecha...

Geoid slopes are computed from models of subduction in which the subducted lithosphere is much stronger than the surrounding mantle. Geoid slope contributions from both the lithospheric slab and mantle boundary deformations are computed from finite element analysis of mantle flow. The finite element model includes a slab of finite length and a dept...

This paper presents precise relative relocations for aftershocks of 59 intermediate and deep earthquakes, using P, pP, and PKP arrival times read by us or reported in the literature. These aftershocks included 36 ``rupture subevents,'' occurring within 1 min of the initial event, and 71 ``true aftershocks,'' occurring later and identified statistic...

We propose simple graphical methods for evaluating whether a set of direction vectors are clustered with respect to particular directions, axes, or planes. As examples of these techniques, we present data concerning the relationship between: (1) aftershock/initial event geometry and nodal planes of focal mech-anisms; (2) aftershock/initial event ge...

Non-hydrostatic concentrations of mass at the surface of the planet have been suggested as mechanisms of permanent reorientation for all of the terrestrial planets and for the Moon. In order for such a load to control planetary orientation, three conditions must be satisfied. The surface load must be non-hydrostatically supported; the surface load...

The orientation of a planet is controlled by the positions of the principal axes of the inertia tensor relative to the planetary surface. Using the theory for the deflection of thin elastic shells the principal axes are computed after emplacement of an arbitrary axisymmetrical load. The partial compensation of the load and the partial relaxation of...

There are many examples of cyclic stratigraphy in the sedimentary record. In some cases this stratigraphy is attributed to periodic variations in sea level. In this paper a harmonic variation in sea level is superimposed on a constant velocity of tectonic subsidence in order to generate synthetic cyclic stratigraphy. Maximum rates of sedimentation...

It is hypothesized that the Tharsis rise can be approximated as an axisymmetrical igneous construct. Linear theory for the deflection of planetary lithospheres is used to demonstrate that the lithospheric stresses required partially to support the construct are reasonable and consistent with the observed radial grabens around Tharsis. The computed...

The existence of mascons on the moon indicates that the lunar elastic lithosphere can support substantial loads for about three billion years. Lunar topography also appears to be uncompensated. Observations of gravity on Mars show that the Tharsis uplift is only partially compensated. A number of authors have attributed this support to lithospheric...

The role of membrane stresses and bending stresses in supporting topographic loads on planetary elastic lithospheres is examined. A dimensionless parameter is introduced in order to determine the ability of a spherical shell to support loads through membrane stresses. It is determined that when this parameter is large, membrane stresses can fully s...

Compared to the early 1990's, when the IMS was being designed, in 2005 data from many times more seismographic stations are freely and openly available in near real time. The rapid, ongoing growth in open data both contributes research to improve methods of seismological monitoring and makes detection of an underground nuclear test progressively mo...

Nuclear explosion monitoring is as important today as it was at the dawn of the atomic age. Over the past several decades the scientific understanding and technological sophistication that underpin monitoring have advanced tremendously. We still face challenges, however, because the United States (U.S.) needs to monitor a growing range of events, f...