Kevin Fleming

Modeling the dynamic component of the geoid and topography of Venus

[1] We analyze the Venusian geoid and topography to determine the relative importance of isostatic, elastic and dynamic compensation mechanisms over different degree ranges. The geoid power spectrum plotted on a log-log scale shows a significant change in its slope at about degree 40, suggesting a transition from a predominantly dynamic compensation mechanism at lower degrees to an isostatic and/or elastic mechanism at higher degrees. We focus on the dynamic compensation in the lower-degree interval. We assume that (1) the flow is whole mantle in style, (2) the long-wavelength geoid and topography are of purely dynamic origin, and (3) the density structure of Venus’ mantle can be approximated by a model in which the mass anomaly distribution does not vary with depth. Solving the inverse problem for viscosity within the framework of internal loading theory, we determine the families of viscosity models that are consistent with the observed geoid and topography between degrees 2 and 40. We find that a good fit to the data can be obtained not only for an isoviscous mantle without a pronounced lithosphere, as suggested in some previous studies, but also for models with a high-viscosity lithosphere and a gradual increase in viscosity with depth in the mantle. The overall viscosity increase across the mantle found for the latter group of models is only partially resolved, but profiles with a � 100-km-thick lithosphere and a viscosity increasing with depth by a factor of 10‐80, hence similar to viscosity profiles expected in the Earth’s mantle, are among the best fitting models.

Geodetic measurements reveal similarities between post-Last Glacial Maximum and present-day mass loss from the Greenland ice sheet.

Present destabilization of marine-based sectors in Greenland may increase sea level for centuries to come. Accurate quantification of the millennial-scale mass balance of the Greenland ice sheet (GrIS) and its contribution to global sea-level rise remain challenging because of sparse in situ observations in key regions. Glacial isostatic adjustment (GIA) is the ongoing response of the solid Earth to ice and ocean load changes occurring since the Last Glacial Maximum (LGM; ~21 thousand years ago) and may be used to constrain the GrIS deglaciation history. We use data from the Greenland Global Positioning System network to directly measure GIA and estimate basin-wide mass changes since the LGM. Unpredicted, large GIA uplift rates of +12 mm/year are found in southeast Greenland. These rates are due to low upper mantle viscosity in the region, from when Greenland passed over the Iceland hot spot about 40 million years ago. This region of concentrated soft rheology has a profound influence on reconstructing the deglaciation history of Greenland. We reevaluate the evolution of the GrIS since LGM and obtain a loss of 1.5-m sea-level equivalent from the northwest and southeast. These same sectors are dominating modern mass loss. We suggest that the present destabilization of these marine-based sectors may increase sea level for centuries to come. Our new deglaciation history and GIA uplift estimates suggest that studies that use the Gravity Recovery and Climate Experiment satellite mission to infer present-day changes in the GrIS may have erroneously corrected for GIA and underestimated the mass loss by about 20 gigatons/year.

A wireless mesh sensing network for early warning

Earthquake early warning systems should provide reliable warnings as quickly as possible with a minimum number of false and missed alarms. Wireless meshed networks, coupled with low-cost seismometers for monitoring, evaluation, and information about seismic vibrations in space and time are introducing a new generation of warning infrastructures for mega-cities. The use of a cooperative method for signal analysis makes it possible to distinguish earthquakes (with a certain minimal magnitude) from other ground shaking in a city. The paper gives a short overview of our approach for developing decentralized early warning systems and an evaluation based on experiences gained from model investigations, testbeds in Berlin, and prototype installations in Istanbul.

A three-level framework for multi-risk assessment

The effective management of the risks posed by natural and man-made hazards requires all relevant threats and their interactions to be considered. This paper proposes a three-level framework for multi-risk assessment that accounts for possible hazard and risk interactions. The first level is a flow chart that guides the user in deciding whether a multi-hazard and risk approach is required. The second level is a semi-quantitative approach to explore if a more detailed, quantitative assessment is needed. The third level is a detailed quantitative multi-risk analysis based on Bayesian networks. Examples that demonstrate the application of the method are presented.

Geoid displacement about Greenland resulting from past and present- day mass changes in the Greenland Ice Sheet

[1] Predictions are presented of secular changes in the geoid arising from glacial-isostatic adjustment (GIA) following the Last Glacial Maximum and from presentday mass changes in the Greenland Ice Sheet (GIS). Geoid displacement from ongoing GIA is dominated by ice-load changes outside of Greenland at lower spherical-harmonic degrees ( 2000 m). Spatial variability is noted when the presentday GIS response is expanded to degree and order 32. This is detectable by GRACE when assuming an optimistic accuracy, but is too small by a factor of ca. 3 for an alternate accuracy estimate. Present-day GIS geoid displacement rates are generally less than the equivalent response from ice-mass changes in Antarctica, Patagonia and Alaska. INDEX TERMS: 1299 Geodesy and Gravity: General or miscellaneous; 1645 Global Change: Solid Earth; 1827 Hydrology: Glaciology (1863). Citation: Fleming, K., Z. Martinec, and J. Hagedoorn (2004), Geoid displacement about Greenland resulting from past and present-day mass changes in the Greenland Ice Sheet, Geophys. Res. Lett., 31, L06617,

Comparing the version 7 TRMM 3B43 monthly precipitation product with the TRMM 3B43 version 6/6A and Bureau of Meteorology datasets for Australia

Recently, Fleming et al. (2011) compared the Tropical Rainfall Measuring Mission (TRMM) 3B43 (version 6/6A) monthly product with the Australian Bureau of Meteorology (the Bureau) monthly gridded dataset for the period 1998 to 2010. They found that the two datasets generally show a strong spatial and temporal agreement with each other. Since then, a new release (version 7) of the TRMM 3B43 product has been made available. This note briefly compares the 3B43 versions 6/6A and 7 (3B43 v6/6A and v7, respectively) products to that provided by the Bureau within the context of the previous work of Fleming et al. (2011). It is found that 3B43 v7 displays an improved correlation with the Bureau dataset compared to 3B43 v6/6A, with a cross correlation for the entire time series of 0.970 for 3B43 v7 versus the Bureau, compared to 0.932 for 3B43 v6/6A versus the Bureau. This improvement is especially noticeable for several months (October 2006, January 2007, and October 2008) where 3B43 v6/6A showed a relatively poor correlation with the Bureau dataset. However, the generally decreased correlation and increased scatter between 3B43 v6/6A and the Bureau after 2004 was also noted with 3B43 v7, although not as strongly, with a cross correlation for the period 1998 to 2003 of 0.947 and 0.976 for 3B43 v6/6A and v7 versus the Bureau, respectively, while 0.919 and 0.965 are the corresponding values for the period between 2004 and 2010. The reason for the improvement in the results is beyond the scope of this work, but there were several modifications to the 3B43 processing, including the improved treatment of the rain gauge input. We therefore recommend that workers employing this TRMM product change to the latest version for their studies.

Perspectives on global dynamic exposure modelling for geo-risk assessment

The need for a global approach to natural hazard and risk assessment is becoming increasingly apparent to the disaster risk reduction community. Different natural (e.g. earthquakes, tsunamis, tornadoes) and anthropogenic (e.g. industrial accidents) hazards threaten millions of people every day all over the world. Yet, while hazards can be so different from each other, the exposed assets are mostly the same: populations, buildings, infrastructure and the environment. Exposure should be regarded as a dynamic process, as best exemplified by rapid urbanization, depopulation of rural areas and all of the changes associated with the actual evolution of the settlements themselves. The challenge is thus to find innovative, efficient methods to collect, organize, store and communicate exposure data on a global scale, while also accounting for its inherent spatio-temporal dynamics. The aim of this paper is to assess the challenge of implementing an exposure model at a global scale, suitable for different geo-hazards within a dynamic and scalable framework. In this context, emerging technologies, from remote sensing to crowd-sourcing, are assessed for their usability in exposure modelling and a road map is laid out towards a global exposure model that will continuously evolve over time by the continuous input and updating of data, including the consideration of uncertainties. Such an exposure model would lay the basis for global vulnerability and risk assessments by providing reliable, standardized information on the exposed assets across a range of different hazards.

The effect of melting land-based ice masses on sea-level around the Australian coastline

Changes in relative sea-level (RSL) are generally caused by variations in sea surface heights from steric effects (thermal expansion and salinity changes) and the mechanical response of the Earth to past and current redistributions of ice and water between land and oceans. This paper focuses on the latter, where we present scenario calculations of the spatial variability in present-day RSL change around the Australian coastline resulting from melting land-based ice masses. Three scenarios are investigated: (1) the ongoing effect of glacial isostatic adjustment (GIA) arising from ice- and water-load redistribution during the last glacial–interglacial transition; (2) the effect of present-day changes in the Greenland and West and East Antarctic ice sheets (GIS, WAIS and EAIS, respectively) and two regions of major mountain glaciation, Alaska and Patagonia; and (3) a hypothetical complete melting of the GIS, WAIS and EAIS occurring over 5000 years. The first scenario shows falling RSL around Australia of the order of 0.4 to 1.2 times the average value around the coast (equivalent to a RSL fall of between 0.2 and 0.6 mm/a). For the second scenario, the spatial variability is strongly dependent upon the location of each ice mass relative to Australia. For Greenland and Patagonia, the resulting changes to the Earths rotation strongly affect the spatial variability, while the direct gravitational effect is more important when considering the Antarctic ice sheets. The variability associated with the first two scenarios becomes clearer when examining RSL change estimates for the locations of tide-gauge stations around the Australian coast, especially for the ongoing GIA (a south-to-north increase in the simulated rate of RSL change), the WAIS (east-to-west increase) and the EAIS (south-to-north increase), with the melting of the EAIS potentially having the greatest influence on the variability of the melting land-based ice contribution to RSL change around Australia. The spatial variability associated with the third scenario is strongly influenced over century-length time-scales by the resulting changes in the Earths rotation and the direct gravitational attraction of the ice masses, while after several thousand years the uplift of the continent by mantle material displaced towards it by increased ocean loading becomes more prominent. It must, however, be kept in mind that the spatial variability associated with these scenarios is generally a small proportion of the total RSL change, and that the steric (especially thermosteric) contribution is not included in these results.

Multi-risk approach and urban resilience

Purpose Urban resilience is becoming increasingly important due to increasing degree of urbanization and a combination of several factors affecting urban vulnerability. Urban resilience is also understood as a capacity of a system to prepare, respond and recover from multi-hazard threats. The purpose of multi-risk approach (MRA) is to take into consideration interdependencies between multiple risks, which can trigger a chain of natural and manmade events with different spatial and temporal scales. The purpose of this study is to understand correlation between multi-risk approach and urban resilience. Design/methodology/approach To increase urban resilience, MRA should also include multi-risk governance, which is based on understanding how existing institutional and governance structures, individual judgments and communication of risk assessment results shape decision-making processes. Findings This paper is based on extensive fieldwork in the test studies of Naples, Italy and Guadeloupe, France, the historical case study analysis and the stakeholders’ interviews, workshops and focus groups discussions. Originality/value Multi-risk is a relatively new field in science, only partially developed in social and geosciences. The originality of this research is in establishment of a link between MRA, including both assessment and governance, and urban resilience. In this paper, the authors take a holistic and systemic look at the MRA, including all stages of knowledge generation and decision-making. Both, knowledge generation and decision-making are reinforced by behavioural biases, different perceptions and institutional factors. Further on, the authors develop recommendations on how an MRA can contribute to urban resilience.

The Multi-Parameter Wireless Sensing System (MPwise): Its Description and Application to Earthquake Risk Mitigation

The Multi-Parameter Wireless Sensing (MPwise) system is an innovative instrumental design that allows different sensor types to be combined with relatively high-performance computing and communications components. These units, which incorporate off-the-shelf components, can undertake complex information integration and processing tasks at the individual unit or node level (when used in a network), allowing the establishment of networks that are linked by advanced, robust and rapid communications routing and network topologies. The system (and its predecessors) was originally designed for earthquake risk mitigation, including earthquake early warning (EEW), rapid response actions, structural health monitoring, and site-effect characterization. For EEW, MPwise units are capable of on-site, decentralized, independent analysis of the recorded ground motion and based on this, may issue an appropriate warning, either by the unit itself or transmitted throughout a network by dedicated alarming procedures. The multi-sensor capabilities of the system allow it to be instrumented with standard strong- and weak-motion sensors, broadband sensors, MEMS (namely accelerometers), cameras, temperature and humidity sensors, and GNSS receivers. In this work, the MPwise hardware, software and communications schema are described, as well as an overview of its possible applications. While focusing on earthquake risk mitigation actions, the aim in the future is to expand its capabilities towards a more multi-hazard and risk mitigation role. Overall, MPwise offers considerable flexibility and has great potential in contributing to natural hazard risk mitigation.