Editorial: Pre-earthquake observations and methods for earthquake forecasting and seismic hazard reduction

Understanding the governing principles, which include long-term tectonic loading,
sluggish nucleation, and rapid fracture propagation, enables estimation of the stress level and
change during geophysical observations in seismically active locations. The first step in
earthquake forecasting is the identification of those factors whose space-time dynamics can
be linked to the crustal deformations that precede earthquakes. Significant progresses have
been made in analysing earthquake spatial-temporal correlations, clustering, and the
development of seismicity patterns, paving the way for the possibility of earthquake
prediction. In addition, earthquake physics addresses fundamental questions in
seismology, such as how earthquakes form, how seismic rupture begins, propagates, and
ends, what role long-term and short-term processes play in earthquake triggering, what role
fluids play in earthquake triggering, and what relationship exists between fault dynamics,
energy, friction, and other physical parameters of the focal zone. Recent advances in
seismological and non-seismological observations have resulted in a variety of data,
which have significantly increased our ability to investigate earthquake-related processes
at multiple scales. In addition to established earthquake occurrence patterns and
probabilistic models, a wealth of newly accessible non-seismological data gathered on a
global scale has opened new roads for systematic study and model validation. Ground-based
or satellite-based geophysical and geochemical observations, ranging from ground
deformation patterns to pre-earthquake changes (geochemical, electromagnetic,
hydrogeological, geodetic, etc.), may be related to stress variations in the lithosphere
preceding a large earthquake. A critical reevaluation of proposed techniques in conjunction with state-of-the-art and original observations has been
carried out in this volume with the purpose to identify most
promising future research directions. The primary objective of
the Frontiers in Earth Sciences Research Topic on Pre-
Earthquake Observations and Methods for Earthquake
Forecasting and Seismic Hazard Reduction is to provide an upto-
date view of the processes preceding earthquake occurrence that
can be applied to the design of earthquake forecasting experiments
aimed at validating their accuracy in desirable Test Site areas. The
growing number of articles and Research Topic devoted to
earthquake forecasting, attests to a new attitude towards
earthquake forecasting. New observables are constantly proposed,
taking advantage from the large amount of data provided by new
Earth observation systems and from increased computational
power. Nonetheless, efforts to convert such elusive data into
precisely defined ones are still limited. Operational earthquake
forecasting methods, in particular, should be testable and
confirmed by evidence. The set of errors, namely, the rates of
failure and the space-time extent of alarms, in comparison to those
obtained from the same number of random guess trials, allows for
the evaluation of the effectiveness of the forecasting method. A
necessary emphasis has been devoted on continuous statistical
testing of the relevance and confidence of the precursors in order to
evaluate and continue to improve the performance of the forecasts.
Observations and physical models suggest that several processes in
the lithosphere of the Earth are predictable, but only after extensive
averaging and up to a certain limit. Consequently, earthquake
forecasting necessitates a holistic approach and should be posed as
an integrated,multi-scale process, narrowing themagnitude range,
expected territory, and time of occurrence within the constraints
imposed by physics and data uncertainties. Understanding
governing laws, ranging from long-term tectonic loading and
slow nucleation to rapid rupture propagation, can aid in
estimating the stress state and temporal evolution of
geophysical observables in seismically active regions. Reducing
the space-time uncertainty of forecasts requires the use of
additional, independent, and trustworthy information, which
can be provided by multidisciplinary observations and
recording of natural observables at various space-time scales.
With this Research Topic, we present the current state of
research Pre-Earthquake Observations and Methods for
Earthquake Forecasting and Seismic Hazard Reduction, with a
particular emphasis on:
a) Systematic analysis, physical interpretation, and modeling of preearthquake
processes; Yun Zhou, Lisheng Xu, Jianping Wu,
Chunlai Li, Lihua Fang, and Pan Pan, Seismicity of the
repeating earthquake clusters in the northern Xiaojiang fault
zone and its implications.
Jing Zhao, Zhengyi Yuan, Jinwei Ren, Zaisen Jiang, Qi Yao,
Zhihua Zhou, Chong Yue, Jun Zhong, and Anfu Niu,
Acceleration of deep slip along the Longmenshan fault plane
before the 2008 M8.0 Wenchuan earthquake.
b) Model validation and statistical assessment of proposed physicalbased
precursors; Zhiwei Zhang, Chuntao Liang, Feng Liong,
Min Zhao, and Di Wang, Spatiotemporal Variations of Focal
Mechanism Solutions and Stress Field of the 2019 Changning
Ms6.0 Earthquake Sequence.
c) Statistical methods and issues in earthquake forecast validation;
Renata Rotondi and Elisa Varini, Temporal variations of the
probability distribution of Voronoi cells generated by earthquake
epicenters.
Chong Yue, Ping Ji, Yali Wang, Huaizhong Yu, Jin Cui, Chen Yu,
and Yuchuan Ma, Evolution characteristics and mechanism of
the Load/Unload Response Ratio based on strain observation
before the Jiuzhaigou MS7.0 earthquake.
d) Analysis of input data and requirements for real-time model
testing; Jinhan Xie, Shanshan Yong, Xi’an Wang, Zhenyu Bao,
Yibin Liu, Xing Zhang, and Chunjiu He, Weekly earthquake
prediction in a region of China based on an intensive precursor
network AETA.
e) Time-dependent seismic hazard assessment based on space-time
characterization of impending earthquakes; Aybige Akinci, Irene
Munafò, and Luca Malagnini, S-wave Attenuation Variation and
its impact on Ground Motion Amplitudes during
2016–2017 Central Italy Earthquake Sequence.
f) Geophysical interpretation of non-seismological parameters
associated with crustal deformation processes Yang Xing,
Zhang Tie-bao, Lu Qian, Long Feng, Liang Ming-Jian, Wu
Wei-Wei, Gong Yue, Wei Jia-Xi, and Wu Jia, Variation of
thermal infrared brightness temperature anomalies in the
Madoi earthquake and associated earthquakes in the Tibetan
Plateau (China);
Jinhan Xie, Shanshan Yong, Xi’an Wang, Zhenyu Bao, Yibin Liu,
Xing Zhang, and Chunjiu He
Mehdi Akhoondzadeh, Angelo De Santis, Dedalo Marchetti, and
Xuhui Shen, Swarm-TEC satellite measurements as a potential
earthquake precursor together with other Swarm and CSES data:
the case of Mw7.6 2019 Papua New Guinea seismic event.
Pan Xiong, Cheng Long, Huiyu Zhou, Roberto Battiston, Angelo
De Santis, Dimitar Ouzounov, Xuemin Zhang, and Xuhui Shen,
Pre-earthquake ionospheric perturbation identification using
CSES data via transfer learning.
g) Time series analysis of geophysical and geochemical parameters;
Chenhua Li, Xiaocheng Zhou, Jingchao Li, Lei Liu, Hejun Su,
Ying Li, Miao He, Jinyuan Dong, Jiao Tian, Huiling Zhou, Gang
Gao, Caiyan Zhang, and Zhixin Luo, Hydrogeochemical
Characteristics of Thermal Springs in the Qilian-Haiyuan
Fault Zone at northeast Tibetan Plateau: Role of fluids and
seismic activity.
h) Modeling of pressure fluctuation in deformation processes; Wei Shi,
Hanchao Jiang, G. Ian Alsop, and Guo Wu, A continuous 13.3-ka
paleoseismic record constrains major earthquake recurrence in the
Longmen Shan collision zone.
i) Slow-slip geodetic precursors; Jiangtao Qiu, Lingyun Ji, Liangyu
Zhu, and Qingliang Wang, Present-day tectonic deformation
partitioning across south Tianshan from satellite geodetic imaging.
j) Modeling of chemical and physical parameter variations in
faulted regions; Guo Guangmeng, On the relation between
anomalous clouds and earthquakes in Italian land.
k) Spatial and temporal variation of geochemical and hydrogeological
features in seismic areas and their relationship to faults and seismic
activity Mingbo Yang, Guiping Liu, Zhe Liu, Jingchen Ma, Zhiguo
Wang, Peixue Hua, Xiaoru Sun, Kongyan Han, Bowen Cui, and
Xiaodong Wu,Geochemical Characteristics ofGeothermal and Hot
Spring Gases in Beijing and Zhangjiakou-Bohai Fault Zone.
l) How possible scientific results on earthquake forecasting may be
provided to decision-makers in a useful way
Xia Chaoxu, Nie Gaozhong, Li Huayue, Fan Xiwei, Zhou Junxue,
Yang Rui, and Zeng Xun, Research on lethal levels of buildings
based on historical seismic data.