ALBERT

Description: Nearly half of Greenland’s mass loss occurs through iceberg calving, but the physical mechanisms operating during calving are poorly known and in situ observations are sparse. We show that calving at Greenland’s Helheim Glacier causes a minutes-long reversal of the glacier’s horizontal flow and a downward deflection of its terminus. The reverse motion results from the horizontal force caused by iceberg capsize and acceleration away from the glacier front. The downward motion results from a hydrodynamic pressure drop behind the capsizing berg, which also causes an upward force on the solid Earth. These forces are the source of glacial earthquakes, globally detectable seismic events whose proper interpretation will allow remote sensing of calving processes occurring at increasing numbers of outlet glaciers in Greenland and Antarctica.

Description: The selection of specific uniform seismic source zones for use in probabilistic seismic hazard analysis is often controversial. Recognizing that a consistent approach to source model development is not always possible, as the information available relating to geology and seismotectonics can vary from region to region, the K-means algorithm for hierarchical cluster analysis can be used to partition regions based on observed seismicity. The Aegean [incorporating Greece, Albania, Former Yugoslav Republic of Macedonia (F.Y.R.O.M.), southern Bulgaria and western Turkey], with its varied seismotectonics and generally high seismicity, is used as an important area ofseismicity in which to develop and demonstrate the application of K-means. Two types of algorithm are considered. The first is a point-source K-means that can be used to partition a catalogue of earthquake hypocentres. The second is a novel line-source development of the algorithm, appropriate in seismology as these are analogues for the traces of active faults, which is then applied to a catalogue of known fault ruptures in the Aegean. The common problems of the K-means methodology are also addressed. Ensemble analyses are used to identify better choices of initial estimates for the cluster centres. A cluster quality index is used to identify the optimum number of clusters, and its robustness assessed when considering different subsets of the observed earthquake catalogue. An alternative approach is also implemented: Monte Carlo seismic hazard analysis is used to compare models with different numbers of clusters with the observed seismicity of the 20th century. Considerable variation is found in the optimum number of clusters identified either by the quality index or by stochastic seismic hazard analysis. Ultimately the K-means partitions of seismicity are developed into source models and their representation of Aegean seismotectonics assessed. The result is that models containing between 20 and 30 clusters emerge as the most appropriate in capturing the spatial variation in hypocentral distribution and fault type in the Aegean.

Description: Applying alternative and different approaches to seismic hazard assessment is instructive. It allows learning from the different outcomes of the different approaches. These outcomes may be mutually reinforcing or diverge, suggest further study and research is needed, or provide new insights into old problems. Herein Java island-scale seismic hazard will be considered by applying different probabilistic approaches to hazard assessment. Results from two distinct methods are provided for Java: 1) primary zoning using K-means partitioning of seismicity into spatial clusters (progressed into zones) which are then developed into seismic hazard maps using Monte Carlo earthquake catalogue simulation, and 2) extreme value analysis applied at a matrix of points throughout a zoneless Java. The latter approach has been used before, the former adopts seismicity partitioning into spatial clusters prior to Monte Carlo modelling and is novel. The earthquake catalogue analysed is NEIC (1973-2006). This catalogue is homogenised to the moment magnitude scale MW and Poisson declustering of fore- and after-shocks applied. The completeness threshold is around 4.9 MW. Shallow earthquakes down to 80 km depth contribute most to the hazard and are partitioned into 1 to K trial clusters of seismicity by minimising the total within cluster distance from seed centroids. Repeated trials produce an optimum partition. A variety of indices can be invoked to try to quantify cluster quality for a given K; in addition to this, it is decided to seek the best value of K by testing the influence of K on ensuing seismic hazard analyses. Monte Carlo synthesis generates synthetic catalogues for each K value, from which peak ground acceleration (PGA) hazards are calculated and compared against results from the observed catalogue to choose acceptable K values. To summarise the results, seismic hazard maps are constructed for two acceptable values of K (8 and 27) for Java from the Poisson declustered catalogue of shallow earthquakes using the Boore, Joyner, Fumal attenuation law. Not surprisingly the smaller value of K with 8 clusters (progressed to zones) produces the smoother hazard map. All of the maps indicate highest hazard around the Sunda Strait and a general expectation in Java Island of 100-300 cm s-2 with one-in-ten chance of exceedance in 50 years.

Description: The Aegean is the most seismically active and tectonically complex region in Europe. Damaging earthquakes have occurred here throughout recorded history, often resulting in considerable loss of life. The Monte Carlo method of probabilistic seismic hazard analysis (PSHA) is used to determine the level of ground motion likely to be exceeded in a given time period. Multiple random simulations of seismicity are generated to calculate, directly, the ground motion for a given site. Within the seismic hazard analysis we explore the impact of different seismic source models, incorporating both uniform zones and distributed seismicity. A new, simplified, seismic source model, derived from seismotectonic interpretation, is presented for the Aegean region. This is combined into the epistemic uncertainty analysis alongside existing source models for the region, and models derived by a K-means cluster analysis approach. Seismic source models derived using the K-means approach offer a degree of objectivity and reproducibility into the otherwise subjective approach of delineating seismic sources using expert judgment. Similar review and analysis is undertaken for the selection of peak ground acceleration (PGA) attenuation models, incorporating into the epistemic analysis Greek-specific models, European models and a Next Generation Attenuation model. Hazard maps for PGA on a “rock” site with a 10% probability of being exceeded in 50 years are produced and different source and attenuation models are compared. These indicate that Greek-specific attenuation models, with their smaller aleatory variability terms, produce lower PGA hazard, whilst recent European models and Next Generation Attenuation (NGA) model produce similar results. The Monte Carlo method is extended further to assimilate epistemic uncertainty into the hazard calculation, thus integrating across several appropriate source and PGA attenuation models. Site condition and fault-type are also integrated into the hazard mapping calculations. These hazard maps are in general agreement with previous maps for the Aegean, recognising the highest hazard in the Ionian Islands, Gulf of Corinth and Hellenic Arc. Peak Ground Accelerations for some sites in these regions reach as high as 500–600 cm s−2 using European/NGA attenuation models, and 400–500 cm s−2 using Greek attenuation models.

Description: The Aegean region overlies a complex tectonic regime that experiences a wide diversity of earthquake behaviour, with enormous disparity in focal mechanism and spatio-temporal distribution. Multiple random earthquake simulations, via Monte Carlo simulation, offer the opportunity to analyse seismic hazard across the Aegean, whilst still allowing for uncertainty in various parameters such as frequency-magnitude relation, maximum magnitude (Mmax) and attenuation relation. They may also enable meaningful determination of hazard (in terms of Peak Ground Acceleration (PGA) and MSK Intensity) with exceedence probabilities significantly smaller than those currently used in standard probabilistic seismic hazard assessment (PSHA) techniques. In addition, these simulations can also be used to conduct sensitivity analyses that will act as a verification process, allowing assumptions regarding the seismic hazard parameters to be continually tested. A catalogue of earthquakes in the Aegean (1900-1999AD) is used as a basis for fitting appropriate models of spatial distribution, frequency-magnitude relation and maximum-magnitude. This has been achieved by random re-sampling of the catalogue, and by random sampling from a Gutenberg-Richter relation fitted to the observed data. Simple hazard analyses for five cities within the Aegean have been undertaken using the earthquake simulations. PGA has been determined using appropriate attenuation relations, and its variability quantified. For each site, the PGA with a 10% probability of exceedence in 50 years is largely consistent with those of current hazard analyses. This may give the user additional confidence in the hazard determined for lower exceedence probabilities.

Description: Pakistan and the western Himalaya is a region of high seismic activity located at the triple junction between the Arabian, Eurasian and Indian plates. Four devastating earthquakes have resulted in significant numbers of fatalities in Pakistan and the surrounding region in the past century (Quetta, 1935; Makran, 1945; Pattan, 1974 and the recent 2005 Kashmir earthquake). It is therefore necessary to develop an understanding of the spatial distribution of seismicity and the potential seismogenic sources across the region. This forms an important basis for the calculation of seismic hazard; a crucial input in seismic design codes needed to begin to effectively mitigate the high earthquake risk in Pakistan. The development of seismogenic source zones for seismic hazard analysis is driven by both geological and seismotectonic inputs. Despite the many developments in seismic hazard in recent decades, the manner in which seismotectonic information feeds the definition of the seismic source can, in many parts of the world including Pakistan and the surrounding regions, remain a subjective process driven primarily by expert judgment. Whilst much research is ongoing to map and characterise active faults in Pakistan, knowledge of the seismogenic properties of the active faults is still incomplete in much of the region. Consequently, seismicity, both historical and instrumental, remains a primary guide to the seismogenic sources of Pakistan. This study utilises a cluster analysis approach for the purposes of identifying spatial differences in seismicity, which can be utilised to form a basis for delineating seismogenic source regions. An effort is made to examine seismicity partitioning for Pakistan with respect to earthquake database, seismic cluster analysis and seismic partitions in a seismic hazard context. A magnitude homogenous earthquake catalogue has been compiled using various available earthquake data. The earthquake catalogue covers a time span from 1930 to 2007 and an area from 23.00° to 39.00°N and 59.00° to 80.00°E. A threshold magnitude of 5.2 is considered for K-means cluster analysis. The current study uses the traditional metrics of cluster quality, in addition to a seismic hazard contextual metric to attempt to constrain the preferred number of clusters found in the data. The spatial distribution of earthquakes from the catalogue was used to define the seismic clusters for Pakistan, which can be used further in the process of defining seismogenic sources and corresponding earthquake recurrence models for estimates of seismic hazard and risk in Pakistan. Consideration of the different approaches to cluster validation in a seismic hazard context suggests that Pakistan may be divided into K = 19 seismic clusters, including some portions of the neighbouring countries of Afghanistan, Tajikistan and India.

Description: GNS Science Te Pū Ao, through its GeoNet programme, operates a multidisciplinary sensor network to monitor geological hazards in Aotearoa New Zealand. Data from more than 800 permanent monitoring sites are continuously collected, transformed and delivered to a range of end users.Managing multidisciplinary instrument metadata is a key task of the GeoNet datacentre. In 2017 GeoNet moved away from using a corporate relational database to using a modern and novel approach to manage metadata. All of this metadata is freely available and treated as a dataset (DOI: 10.21420/0VY2-C144) to give users access to whatever metadata they need and to improve visibility and usability.This system is at the core of the GeoNet data pipeline and allows the data transformation process, from the field to end users, to be automated. The system uses a software development approach: a code versioning system based on git and hosted at “github.com/GeoNet/delta” which allows instrument metadata and their changes in time to be peer reviewed, version controlled and checked for consistency. Equipment and installation details are stored as a set of CSV files and short XML seismic response file segments. This allows for easy access and maintenance, with no proprietary external software needed to decode or examine the information.

Description: The Pliocene, specifically the mid-Piacenzian Warm Period (~3.3-3.0 Ma), is widely referred to as a potential analogue for future climate within the palaeoclimate community. The Pliocene is well placed to be a palaeoclimate analogue given that it is the most recent period of sustained warmth above pre-Industrial levels, and that the atmospheric CO2 concentration is similar-to-modern at ~400 ppmv. Results from the Pliocene Model Intercomparison Project (PlioMIP) highlight similarities in large-scale features of Pliocene climate to the future: global mean surface air temperature is ~3°C warmer and global mean total precipitation is ~7% higher than pre-Industrial. However, it is also important to consider how analogous other factors are, such as the drivers of those changes in climate. Using the outputs from a subset of models in PlioMIP2, we show that less-analogous forcings, such as changes to ice sheets and orography, are responsible for 44% of surface air temperature and sea surface temperature change in the Pliocene, and 49% of precipitation change. These forcings must be taken into consideration, and affect how comparable the climate of the Pliocene is to our warmer future. We discuss the implications of these results, and consider what it means for the Pliocene to be a “palaeoclimate analogue”.

Description: Four broad categories capture countries' political and economic barriers to quit coal. Use these to tailor solutions.