Yongxian Zhang

Scalable Multi-variate Analytics of Seismic and Satellite-based Observational Data

Over the past few years, large human populations around the world have been affected by an increase in significant seismic activities. For both conducting basic scientific research and for setting critical government policies, it is crucial to be able to explore and understand seismic and geographical information obtained through all scientific instruments. In this work, we present a visual analytics system that enables explorative visualization of seismic data together with satellite-based observational data, and introduce a suite of visual analytical tools. Seismic and satellite data are integrated temporally and spatially. Users can select temporal ;and spatial ranges to zoom in on specific seismic events, as well as to inspect changes both during and after the events. Tools for designing high dimensional transfer functions have been developed to enable efficient and intuitive comprehension of the multi-modal data. Spread-sheet style comparisons are used for data drill-down as well as presentation. Comparisons between distinct seismic events are also provided for characterizing event-wise differences. Our system has been designed for scalability in terms of data size, complexity (i.e. number of modalities), and varying form factors of display environments.

Characters of variation of LURR during the earthquake sequence of Xinjiang

The theory of the loading/unloading response ratio (LURR) was applied to the Jiashi earthquake sequence which occurred at the beginning of 1997 in Xinjiang, and found that, before the earthquakes with relatively high magnitudes in the sequence, the ratio showed anomalies of high values. That is to say, the LURR theory can be applied to the short-term earthquake prediction in some cases, especially in the early period after a strong earthquake, such as the forecasts for some strong earthquakes in the Jiashi sequence.

Earthquakes and Multi-hazards around the Pacific Rim, Vol. 1: Introduction

The seismic belt along the Pacific Rim is the greatest earthquake zone in the world, generating more than 80% of the world’s largest earthquakes (https://earthquake.usgs.gov/learn/topics/megaqk_facts_fantasy.php). It is also susceptible to tsunamis and volcanic eruptions, which could generate serious multihazards. Since the beginning of the twenty-first century, most countries along the Pacific Rim have suffered from tremendous multi-hazards, especially earthquakes and tsunamis.

Study on the Earthquake Potential Regions in North and Northeast China by Pattern Informatics Method

The Pattern Informatics (PI) method is a new approach to forecast earthquake based on statistical physics. In general, the PI method works for long-term earthquake forecast, but we can obtain the higher spatial resolution of abnormal regions by it. In this paper, we applied the PI method to study seismic risk assessment in north and northeast China. The research suggests that there might be earthquakes with M ges 7 in the juncture of Shanxi, Henan and Shanxi provinces, the juncture of Hebei, Shandong and Henan provinces, and southeast coast of Jiangsu province from Jan. 2009 to Jan. 2050.

The Sensitivity of the Loa/Unload Response Ratio and Critical Region Selection Before Large Earthquakes

Occurrence of a large earthquake could be predicted by anomalous temporal increase of the Load/Unload Response Ratio (LURR). Previous studies have indicated that the stress field that existed before a large earthquake may have a strong influence on the evaluation of LURR. In this paper, we replace the circular region usually adopted in LURR practice with an area within which the tectonic stress change would mostly affect the Coulomb stress on a potential seismogenic fault of a future event. This algorithm is devised to increase the sensitivity of LURR to measure criticality of stress accumulation before a large earthquake. In the algorithm, we assess the stress change and identify the areas with increased Coulomb stress before an earthquake using a simple back-slip dislocation model of the event. Retrospective tests of this algorithm on some disastrous earthquakes that occurred in the Chinese mainland in recent years show remarkable enhancement of the LURR precursory anomalies. By using the hypothetical faults for the large earthquake prediction, we further illustrate that the new algorithm is more sensitive to detect future earthquake of a particular magnitude range and location than the circular region algorithm. Hence, where sufficient information of the regional fault tectonics is given, the Coulomb stress algorithm can be used to augment current LURR technique for seismic hazard estimation.

Earthquakes and Multi-hazards Around the Pacific Rim, Vol. I

Earthquakes and Multi-Hazards Around the Pacific Rim, Vol. II: Introduction -- Subduction Mode Selection During Slab and Mantle Transition Zone Interaction: Numerical Modeling -- Characteristics of Viscoelastic Crustal Deformation Following a Megathrust Earthquake: Discrepancy Between the Apparent and Intrinsic Relaxation Time Constants -- Interpretation of Offshore Crustal Movements Following the 2011 Tohoku-Oki Earthquake by the Combined Effect of Afterslip and Viscoelastic Stress Relaxation -- Rupture Characteristics of the 25 November 2016 Aketao Earthquake (Mw6.6) in Eastern Pamir Revealed by GPS and Teleseismic Data -- Source Characteristics of the Northern Longitudinal Valley, Taiwan Derived from Broadband Strong-Motion Simulation -- Fault Structural Control on Earthquake Strong Ground Motions: the 2008 Wenchuan Earthquake as an Example -- Voids and Rock Friction at Subseismic Slip Velocity -- A Dimensional Analysis Method for Improved Load/Unload Response Ratio -- Natural Time, Nowcasting and the Physics of Earthquakes: Estimation of Seismic Risk to Global Megacities -- Natural Time and Nowcasting Earthquakes: Are Large Global Earthquakes Temporally Clustered? -- Optimal Scaling of Aftershock Zones Using Ground Motion Forecasts -- Probabilistic Seismic Hazard Assessment for Himalayan-Tibetan Region from Historical and Instrumental Earthquake Catalogs -- Scenario-Based Seismic Hazard Analysis for the Xianshuihe Fault Zone, Southwest China -- Tsunami Simulation Method Assimilating Ocean Bottom Pressure Data near a Tsunami Source Region.

Visual exploration of ionosphere disturbances for earthquake research

In seismic research, a hypothesis is that ionosphere disturbances are related to lithosphere activities such as earthquakes. Domain scientists are urgent to discover disturbance patterns of electromagnetic attributes in ionosphere around earthquakes, and to propose related hypotheses. However, the workflow of seismic researchers usually only supports pattern extraction from a few earthquakes. To explore the pattern-based hypotheses on a large spatiotemporal scale meets challenges, due to the limitation of their analysis tools. To tackle the problem, we develop a visual analytics system which not only supports pattern extraction of the original workflow in a way of dynamic query, but also extends the work with hypotheses exploration on a global scale. Domain scientists can easily utilize our system to explore the heterogeneous dataset, and to extract patterns and explore related hypotheses visually and interactively. We conduct several case studies to demonstrate the usage and effectiveness of our system in the research of relationships between ionosphere disturbances and earthquakes.

An Ensemble Approach for Improved Short-to-Intermediate-Term Seismic Potential Evaluation

Pattern informatics (PI), load/unload response ratio (LURR), state vector (SV), and accelerating moment release (AMR) are four previously unrelated subjects, which are sensitive, in varying ways, to the earthquake’s source. Previous studies have indicated that the spatial extent of the stress perturbation caused by an earthquake scales with the moment of the event, allowing us to combine these methods for seismic hazard evaluation. The long-range earthquake forecasting method PI is applied to search for the seismic hotspots and identify the areas where large earthquake could be expected. And the LURR and SV methods are adopted to assess short-to-intermediate-term seismic potential in each of the critical regions derived from the PI hotspots, while the AMR method is used to provide us with asymptotic estimates of time and magnitude of the potential earthquakes. This new approach, by combining the LURR, SV and AMR methods with the choice of identified area of PI hotspots, is devised to augment current techniques for seismic hazard estimation. Using the approach, we tested the strong earthquakes occurred in Yunnan–Sichuan region, China between January 1, 2013 and December 31, 2014. We found that most of the large earthquakes, especially the earthquakes with magnitude greater than 6.0 occurred in the seismic hazard regions predicted. Similar results have been obtained in the prediction of annual earthquake tendency in Chinese mainland in 2014 and 2015. The studies evidenced that the ensemble approach could be a useful tool to detect short-to-intermediate-term precursory information of future large earthquakes.