Achievements and New Frontiers in Research Oriented to Earthquake Forecasting

What happens before an earthquake occurs? Which are the physical processes that take place in the Earth's crust before the earthquake nucleates? How can we observe, describe and model them statistically and physically? During the last decades several efforts have been devoted by geophysical research in an attempt to answer these fundamental questions. Although a clear univocal picture is still missing, a large amount of data and long-term observations accumulated over the time, as well as new methodological approaches, that eventually allow for development and verification of theoretical models. The understanding of governing laws, from long-term tectonic loading and slow nucleation to rapid rupture propagation, is useful to estimate the stress state and evolution during time of geophysical observations around seismically active areas. A preliminary step toward earthquake forecasting is the identification of those parameters (physical, geological, geodetic, seismological and chemical) whose space-time dynamics can be associated with the preparation process of crustal deformations which can be accompanied by earthquakes. Significant steps have been made towards assessing earthquake space-time correlations, clustering, and the emergence of seismicity patterns, showing the potential for reproducible and testable earthquake forecasting.

Seismicity is only one manifestation of Earth's complex dynamics in advance of catastrophic earthquakes. Besides identified patterns and probabilistic models of earthquake occurrence, many newly available non seismological data collected on a global scale provide new opportunities for systematic analysis and model testing. A variety of geophysical and geochemical observations, ranging from ground-related deformation patterns (GPS,SAR, etc.) to pre-earthquake changes (be they geochemical, electromagnetic, hydro-geological, geodetic or thermodynamic), recorded by ground based or by satellite based techniques may be related to stress variations in the lithosphere prior to an eventual large earthquake. What's new after decades of research? An objective reappraisal of proposed methods, along with state-of-the-art and novel observations, may contribute highlighting preferred research paths. The main purpose of the Research Topic of Frontiers in Earth Sciences, focused on pre-earthquake observations, methods and perspectives, is to provide a current view in knowledge of processes preceding earthquakes occurrence, which can be possibly used to set up earthquake forecasting experiments, aimed at their verification both in large or in small Test Site areas.

With this Research Topic we aim to provide a current state of the art in research on processes preceding earthquakes, with a particular focus on:
a) Systematic analysis, physical interpretation and modeling of pre-earthquake processes;
b) Model validation and statistical assessment of proposed physical-based precursors;
c) Statistical methods and problems in earthquake forecast validation;
d) Input data analysis and requirements for real-time model testing;
e) Time-dependent seismic hazard assessment based on space-time characterization of impending earthquakes;
f) Geophysical interpretation of non-seismological parameters linked to crustal deformation processes;
g) Time series analysis of geophysical and geochemical parameters;
h) Modeling of pressure fluctuation in deformating deep reservoirs etc.;
i) Slow-slip geodetic precursors;
j) Modeling of chemical and physical parameters fluctuations in faulted areas; and
k) Spatial and temporal variation of geochemical and hydrogeological characteristics in seismic areas and their correlation to faults and to earthquake activity.

Cover Image credit: Zhaofei Liu and Ying Li from the Institute of Earthquake Forecasting, China