156 research outputs found
Reverse Detection of Short-Term Earthquake Precursors
We introduce a new approach to short-term earthquake prediction based on the
concept of selforganization of seismically active fault networks. That approach
is named "Reverse Detection of Precursors" (RDP), since it considers precursors
in reverse order of their appearance. This makes it possible to detect
precursors undetectable by direct analysis. Possible mechanisms underlying RDP
are outlined. RDP is described with a concrete example: we consider as
short-term precursors the newly introduced chains of earthquakes reflecting the
rise of an earthquake correlation range; and detect (retrospectively) such
chains a few months before two prominent Californian earthquakes - Landers,
1992, M = 7.6, and Hector Mine, 1999, M = 7.3, with one false alarm. Similar
results (described elsewhere) are obtained by RDP for 21 more strong
earthquakes in California (M >= 6.4), Japan (M >= 7.0) and the Eastern
Mediterranean (M >= 6.5). Validation of the RDP approach requires, as always,
prediction in advance for which this study sets up a base. We have the first
case of advance prediction; it was reported before Tokachi-oki earthquake (near
Hokkaido island, Japan), Sept. 25, 2003, M = 8.1. RDP has potentially important
applications to other precursors and to prediction of other critical phenomena
besides earthquakes. In particular, it might vindicate some short-term
precursors, previously rejected as giving too many false alarms.Comment: 17 pages, 5 figure
Predicting Failure using Conditioning on Damage History: Demonstration on Percolation and Hierarchical Fiber Bundles
We formulate the problem of probabilistic predictions of global failure in
the simplest possible model based on site percolation and on one of the
simplest model of time-dependent rupture, a hierarchical fiber bundle model. We
show that conditioning the predictions on the knowledge of the current degree
of damage (occupancy density or number and size of cracks) and on some
information on the largest cluster improves significantly the prediction
accuracy, in particular by allowing to identify those realizations which have
anomalously low or large clusters (cracks). We quantify the prediction gains
using two measures, the relative specific information gain (which is the
variation of entropy obtained by adding new information) and the
root-mean-square of the prediction errors over a large ensemble of
realizations. The bulk of our simulations have been obtained with the
two-dimensional site percolation model on a lattice of size and hold true for other lattice sizes. For the hierarchical fiber
bundle model, conditioning the measures of damage on the information of the
location and size of the largest crack extends significantly the critical
region and the prediction skills. These examples illustrate how on-going damage
can be used as a revelation of both the realization-dependent pre-existing
heterogeneity and the damage scenario undertaken by each specific sample.Comment: 7 pages + 11 figure
Long-term premonitory seismicity patterns in Tibet and the Himalayas
An attempt is made to identify seismicity patterns precursory to great earthquakes in most of Tibet as well as the central and eastern Himalayas. The region has considerable tectonic homogeneity and encompasses parts of China, India, Nepal, Bhutan, Bangladesh, and Burma. Two seismicity patterns previously described were used: (1) pattern ÎŁ is a peak in the sum of earthquake energies raised to the power of about 2/3, taken over a sliding time window and within a magnitude range less than that of events we are trying to predict; and (2) pattern S (swarms) consists of the spatial clustering of earthquakes during a time interval when the seismicity is above average. Within the test region, distinct peaks in pattern ÎŁ have occurred twice during the 78âyearâlong test period: in 1948â49, prior to the great 1950 AssamâTibet earthquake (M = 8.6), and in 1976. Peaks in pattern S have occurred three times; in 1932â1933, prior to the great 1934 BiharâNepal earthquake (M = 8.3), in 1946, and in 1978. The 1934 and 1950 earthquakes were the only events in the region that exceeded M = 8.0 during the test period. On the basis of experience here and elsewhere, the current peaks in both ÎŁ and S suggest the likelihood of an M = 8.0 event within 6 years or an M = 8.5 event within 14 years. Such a prognostication should be viewed more as an experimental longâterm enhancement of the probability that a large earthquake will occur than as an actual prediction, in view of the exceedingly large area encompassed and the very lengthy time window. Furthermore, the chances of a randomly occurring event as large as M = 8.0 in the region are perhaps 21% within the next 6 years, and the present state of the art is such that we can place only limited confidence in such forecasts. The primary impact of the study, in our opinion, should be to stimulate the search for mediumâ and shortâterm precursors in the region and to search for similar longâterm precursors elsewhere
Universality of Cluster Dynamics
We have studied the kinetics of cluster formation for dynamical systems of
dimensions up to interacting through elastic collisions or coalescence.
These systems could serve as possible models for gas kinetics, polymerization
and self-assembly. In the case of elastic collisions, we found that the cluster
size probability distribution undergoes a phase transition at a critical time
which can be predicted from the average time between collisions. This enables
forecasting of rare events based on limited statistical sampling of the
collision dynamics over short time windows. The analysis was extended to
L-normed spaces () to allow for some amount of
interpenetration or volume exclusion. The results for the elastic collisions
are consistent with previously published low-dimensional results in that a
power law is observed for the empirical cluster size distribution at the
critical time. We found that the same power law also exists for all dimensions
, 2D L norms, and even for coalescing collisions in 2D. This
broad universality in behavior may be indicative of a more fundamental process
governing the growth of clusters
On intermediate-term prediction of strong earthquakes in the himalayan arc region using pattern recognition algorithm M8
Seismicity of the Himalayan arc lying within the limits shown in figure 1 and covering the period 1964 to 1987 was scanned using M8 algorithm with a view to identifying the times of increased probabilities (TIPs) of the occurrence of earthquakes of magnitude greater than or equal to 7.0, during the period 1970 to 1987. In this period, TIPs occupy 18% of the space time considered. One of these precedes the only earthquake in this magnitude range which occurred during the period. Two numerical parameters used in the algorithm, namely the magnitude thresholds, had to be altered for the present study owing to incomplete data. Further monitoring of TIPs is however warranted, both for testing the predictive capability of this algorithm in the Himalayan region and for creating a base for the search of short-term precursors
GEMS: the opportunity for stress-forecasting all damaging earthquakes worldwide
A new understanding of rock deformation allows the accumulation of stress before earthquakes to be monitored by using shear-wave splitting to assess stress-induced changes to microcrack geometry. Using swarms of small earthquakes as the source of shear-waves, such stress accumulations have been recognised with hindsight before some fifteen earthquakes worldwide. On one occasion the time, magnitude, and fault-break of an M 5 earthquake was successfully stress-forecast in a comparatively narrow magnitude/time window. However, suitable swarms of small earthquakes are very uncommon, and routine forecasting requires measurements of controlled-source observations at bore-hole Stress-Monitoring Sites (SMSs). A prototype SMS confirmed that both science and technology are effective for monitoring stress changes before earthquakes, and the sensitivity is such that a network of SMSs, on a 400 km-grid, say, could stress-forecast all M â„ 5 earthquakes, that is all damaging earthquakes, within the grid. This paper suggests that a Global Earthquake Monitoring System (GEMS) could forecast all damaging earthquakes in both developing and developed countries worldwide
Application of pattern recognition algorithm in the seismic belts of Indian convergent plate margin - CN algorithm
The earthquake catalogue from 1964 to August 1991 is used to identify the times of increased probabilities (TIPs) of the earthquake mainshocks of magnitudes greater than or equal to 6.4 and are associated with the Indian convergent plate margins, in retrospect. In Pakistan and Indo-Burma regions, the analysis was repeated for magnitude threshold 6.2 and 7.0 respectively. All the earthquakes (except one in the Hindukush region and one in Indo-Burmese region) in Pakistan, Hindukush-Pamir, Himalaya and Indo-Burmese regions were preceded by the special activation and hence were predicted.
Approximately 23 ± 10% of the total time (1970 to August 1991) is occupied by the TIPs in all the regions. The reasons for failure to predict the two earthquakes in these regions are discussed.
Our analysis gives a better picture of the regionalization and the size of the space-time volume for the preparation of an earthquake. The high success ratio of the algorithm proves that it can be applied in this territory for further prediction in the real time, without any significant changes in its parameters
Using synchronization to improve earthquake forecasting in a cellular automaton model
A new forecasting strategy for stochastic systems is introduced. It is
inspired by the concept of anticipated synchronization between pairs of chaotic
oscillators, recently developed in the area of Dynamical Systems, and by the
earthquake forecasting algorithms in which different pattern recognition
functions are used for identifying seismic premonitory phenomena. In the new
strategy, copies (clones) of the original system (the master) are defined, and
they are driven using rules that tend to synchronize them with the master
dynamics. The observation of definite patterns in the state of the clones is
the signal for connecting an alarm in the original system that efficiently
marks the impending occurrence of a catastrophic event. The power of this
method is quantitatively illustrated by forecasting the occurrence of
characteristic earthquakes in the so-called Minimalist Model.Comment: 4 pages, 3 figure
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