Natural time analysis is a statistical method applied to analyze complex time series and critical phenomena, based on event counts as a measure of "time" rather than the clock time. [1] [2] Natural time concept was introduced by P. Varotsos, N. Sarlis and E. Skordas in 2001. [3] Natural time analysis has been primarily applied to earthquake prediction [1] [2] / nowcasting [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] and secondarily to sudden cardiac death [14] / heart failure [15] [16] and financial markets. [17] Natural time characteristics are considered to be unique. [9]
"Natural time" is a new view of time introduced in 2001 [3] that is not continuous, in contrast to conventional time which is in the continuum of real numbers, but instead its values form countable sets as natural numbers. [18]
In natural time domain each event is characterized by two terms, the "natural time" χ, and the energy Qk. χ is defined as k/N, where k is a natural number (the k-th event) and N is the total number of events in the time sequence of data. A related term, pk, is the ratio Qk/Qtotal, which describes the fractional energy released. The term κ1 is the variance in natural time: [19]
Time reversal, in contrast to clock time, is applicable when studying the approach of a system to criticality with natural time analysis. Living systems for example are considered to operate far from equilibrium as there is flow of energy crossing their boundaries, in contrast to deceased organisms where inner driving forces are absent. While time irreversibility is a fundamental property of a living system, the state of death is more time reversible by means of energy flow across the system's boundaries. Thus a critical state of a system can be estimated by applying natural time analysis upon calculating the entropy upon both normal time flow and time reversal and studying the difference of the two results. [15] [14] [16]
Natural time analysis has been initially applied to VAN method in order to improve the accuracy of the estimation of the time of a forthcoming earthquake that has been indicated to occur by seismic electric signals (SES). The method deems SES valid when κ1 = 0.070. Once the SES are deemed valid, a second NT analysis is started in which the subsequent seismic (rather than electric) events are noted, and the region is divided up as a Venn diagram with at least two seismic events per overlapping rectangle. When κ1 approaches the value κ1 = 0.070 for the candidate region, a critical seismic event is considered imminent, i.e. it will occur in a few days to one week or so. [20]
In seismology, nowcasting is the estimate of the current dynamic state of a seismological system. [4] [7] It differs from forecasting which aims to estimate the probability of a future event [12] but it is also considered a potential base for forecasting. [8] [4] Nowcasting is based on the earthquake cycle model, a recurring cycle between pairs of large earthquakes in a geographical area, upon which the system is evaluated using natural time. [4] Nowcasting calculations produce the "earthquake potential score", an estimation of the current level of seismic progress. [9]
When applied to seismicity, natural time has the following advantages: [4]
Typical applications are: great global earthquakes and tsunamis, [5] aftershocks and induced seismicity, [8] [13] induced seismicity at gas fields, [10] seismic risk to global megacities, [12] studying of clustering of large global earthquakes, [11] etc.
Natural time analysis has been experimentally used for the diagnosis of heart failure syndrome [15] [16] as well as identifying patients at high risk for sudden cardiac death, [14] even when measuring solely the heart rate, either using electrocardiography or far more inexpensive and portable equipment (i.e. oximeter). [16]
Due to similarities of the dynamic characteristics between earthquakes and financial markets, natural time analysis, which is primarily used in seismology, was chosen to assist in developing winning strategies in financial markets, with encouraging results. [17]
Seismology is the scientific study of earthquakes and the generation and propagation of elastic waves through the Earth or other planetary bodies. It also includes studies of earthquake environmental effects such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, glacial, fluvial, oceanic microseism, atmospheric, and artificial processes such as explosions and human activities. A related field that uses geology to infer information regarding past earthquakes is paleoseismology. A recording of Earth motion as a function of time, created by a seismograph is called a seismogram. A seismologist is a scientist works in basic or applied seismology.
Earthquake prediction is a branch of the science of seismology concerned with the specification of the time, location, and magnitude of future earthquakes within stated limits, and particularly "the determination of parameters for the next strong earthquake to occur in a region". Earthquake prediction is sometimes distinguished from earthquake forecasting, which can be defined as the probabilistic assessment of general earthquake hazard, including the frequency and magnitude of damaging earthquakes in a given area over years or decades. Not all scientists distinguish "prediction" and "forecast", but the distinction is useful.
Induced seismicity is typically earthquakes and tremors that are caused by human activity that alters the stresses and strains on Earth's crust. Most induced seismicity is of a low magnitude. A few sites regularly have larger quakes, such as The Geysers geothermal plant in California which averaged two M4 events and 15 M3 events every year from 2004 to 2009. The Human-Induced Earthquake Database (HiQuake) documents all reported cases of induced seismicity proposed on scientific grounds and is the most complete compilation of its kind.
A seismic gap is a segment of an active fault known to produce significant earthquakes that has not slipped in an unusually long time, compared with other segments along the same structure. There is a hypothesis or theory that states that over long periods, the displacement on any segment must be equal to that experienced by all the other parts of the fault. Any large and longstanding gap is, therefore, considered to be the fault segment most likely to suffer future earthquakes.
Panayiotis Varotsos is a Greek physicist and former professor in the Department of Physics of the University of Athens, notable for his VAN method to predict earthquakes.
The VAN method – named after P. Varotsos, K. Alexopoulos and K. Nomicos, authors of the 1981 papers describing it – measures low frequency electric signals, termed "seismic electric signals" (SES), by which Varotsos and several colleagues claimed to have successfully predicted earthquakes in Greece. Both the method itself and the manner by which successful predictions were claimed have been severely criticized. Supporters of VAN have responded to the criticism but the critics have not retracted their views.
In seismology, the Gutenberg–Richter law expresses the relationship between the magnitude and total number of earthquakes in any given region and time period of at least that magnitude.
QuakeSim is a NASA project for modeling earthquake fault systems. It was started in 2001 with NASA funding as a follow-up to the General Earthquake Models (GEM) initiative. The multi-scale nature of earthquakes requires integrating data types and models to fully simulate and understand the earthquake process. QuakeSim is a computational framework for modeling and understanding earthquake and tectonic processes.
This list of 20th-century earthquakes is a list of earthquakes of magnitude 6 and above that occurred in the 20th century. Sone smaller events which nevertheless had a significant impact are also included. After 1900 most earthquakes have some degree of instrumental records and this means that the locations and magnitudes are more reliable than for earlier events.
The Sunda megathrust is a fault that extends approximately 5,500 km (3300 mi) from Myanmar (Burma) in the north, running along the southwestern side of Sumatra, to the south of Java and Bali before terminating near Australia. It is a megathrust, located at a convergent plate boundary where it forms the interface between the overriding Eurasian plate and the subducting Indo-Australian plate. It is one of the most seismogenic structures on Earth, being responsible for many great and giant earthquakes, including the 2004 Indian Ocean earthquake and tsunami that killed over 227,000 people. The Sunda megathrust can be divided into the Andaman Megathrust, Sumatra(n) Megathrust and Java(n) Megathrust. The Bali-Sumbawa segment is much less active and therefore does not have the "megathrust" term associated with it.
Seismo-electromagnetics are various electro-magnetic phenomena believed to be generated by tectonic forces acting on the Earth's crust, and possibly associated with seismic activity such as earthquakes and volcanoes. Study of these has been prompted by the prospect they might be generated by the increased stress leading up to an earthquake, and might thereby provide a basis for short-term earthquake prediction. However, despite many studies, no form of seismo-electromagnetics has been shown to be effective for earthquake prediction. A key problem is that earthquakes themselves produce relatively weak electromagnetic phenomena, and the effects from any precursory phenomena are likely to be too weak to measure. Close monitoring of the Parkfield earthquake revealed no significant pre-seismic electromagnetic effects. However, some researchers remain optimistic, and searches for seismo-electromagnetic earthquake precursors continue.
The 2010 Beni-Ilmane earthquakes began 14 May at 12:29:22 UTC, when a Mw 5.3 strike-slip earthquake occurred in Northern Algeria. With a maximum EMS-98 intensity of VII (Damaging), it was the first in a sequence of three shocks that affected the Bouïra Province over a ten-day period. Two people were killed, forty-three were injured, and some structural damage was reported.
In seismology, a tsunami earthquake is an earthquake which triggers a tsunami of significantly greater magnitude, as measured by shorter-period seismic waves. The term was introduced by Japanese seismologist Hiroo Kanamori in 1972. Such events are a result of relatively slow rupture velocities. They are particularly dangerous as a large tsunami may arrive at a coastline with little or no warning.
The Environmental Seismic Intensity scale is a seismic scale used for measuring the intensity of an earthquake on the basis of the effects of the earthquake on the natural environment.
The 1999 Aïn Témouchent earthquake occurred on December 22 at 18:36:56 local time in northern Algeria. The dip-slip event had a moment magnitude of 5.6 and a maximum Mercalli intensity of VII. At least 22 were killed, 175 were injured, and 15,000 were homeless. The Belgian Centre for Research on the Epidemiology of Disasters' EM-DAT database and the USGS' National Geophysical Data Center both list financial losses of $60.93 million.
Pica gap is a segment in the Central Volcanic Zone of Chile where volcanic activity is absent. It is named after the Altos de Pica region.
With the development of both conventional and unconventional resources in Canada, induced seismicity caused by anthropological activities has been observed, documented, and studied.
The 1907 Sumatra earthquake occurred on January 4 at 05:19:12 UTC. The estimated magnitude is 7.5–8.0 Ms, with an epicentre close to Simeulue, off Sumatra. It triggered a widespread and damaging tsunami that caused at least 2,188 deaths. The low observed intensity compared to the size of the tsunami has led to its interpretation as a tsunami earthquake. Higher levels of shaking observed on Nias are attributed to a large aftershock, less than an hour later. The tsunami gave rise to the S'mong legend, which is credited with saving many lives during the 2004 earthquake.
R. Paul Young, FREng, FRSC, is a geophysicist and Professor who works in rock mechanics using induced seismicity to monitor fractures and rock damage for engineering applications in mining and radioactive waste management.
The 1986 Kalamata earthquake struck the southern Peloponnese Region of Greece on September 13 at 20:24 local time. The 12.5 km (7.8 mi) deep moment magnitude (Mw ) 5.9 earthquake had an epicenter near the coastal city of Kalamata and was assigned X (Extreme) on the Mercalli intensity scale. The earthquake was the result of normal faulting along a northwest-dipping fault and produced surface ruptures. Extensive damage was reported in Kalamata and Elaiochori. At least 20 people died and 330 were injured. Survivors sought refuge at campsites and reconstruction work lasted five years.
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