Evaluation of Proposed Earthquake Precursors

98 Pages·7.889 MB·English

Evaluation of Proposed
Earthquake Precursors
Max Wyss
Editor
American Geophysical Union
Library of Congress Cataloging in Publication Data
Evaluation of proposed earthquake precursors / M. Wyss, chairman,
p. cm.
ISBN 0-87590-784-9
1. Earthquake prediction—Evaluation. I. Wyss, Max, 1939—
II. American Geophysical Union.
QE538.8.E82 1991
551.2'2—dc20 91-19905
CIP
ISBN 0-87590-784-9
Copyright 1991 American Geophysical Union. Figures, tables and
short excerpts may be reprinted in scientific books and journals if
the source is properly cited; all other rights reserved.
Printed in the United States of America.
American Geophysical Union
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Washington, D.C. 20009
EVALUATION OF PROPOSED EARTHQUAKE PRECURSORS
Conducted 1989/1990 by the IASPEI Sub-commission on Earthquake Prediction
with the help of its working groups, evaluation panels and reviewers.
*M. Wyss, Chairman
Cooperative Institute for Research in Environmental Sciences
and Department of Geological Sciences
University of Colorado
Campus Box 449
Boulder, CO 80309-0449
•now with the
Geophysical Institute
University of Alaska
Fairbanks, AL 99775-0800
Q IASPEI
IASPEI SUB-COMMISSION ON EARTHQUAKE PREDICTION
(Subjects of working groups are indicated)
M. Wyss (Chairman)
Chen Yong (Vice-Chairman)
Time Dependent Seismic Hazard
J. Lomnitz-Adler (Mexico)
D. A. Rhoades (New Zealand)
Crustal Deformations
J. Zschau (W. Germany)
V. Lagios (Greece)
T. Kato (Japan)
Seismicity Patterns
K. Hamada (Japan)
K. Khattri (India)
Combining Parameters for Earthquake Prediction
G. Sobolev (USSR)
K. Tsumura (Japan)
Anomalies Related To Rock Properties
H. Wakita (Japan)
D. Booth (Scotland)
Table of Contents
Introduction
Reviewed Precursor Nominations
Preliminary List of Significant Earthquake Precursors
Nominations without a Decision
Nominations Which Are Not Placed on the Preliminary List at This Time
Special Publications Evaluation of Proposed Earthquake Precursors Vol. 32
INTRODUCTION
Purpose. The Preliminary List of Significant Earthquake Precur­ standards expected for future work. Also, some items that did not
sors (the List) is intended to serve as a preliminary assessment of qualify for the preliminary list may develop enough during the
the state of the art in the identification of earthquake precursors next few years to be accepted in the future.
which may be useful in earthquake prediction attempts. It will be
Evaluation process. The evaluation process established by the
updated periodically during the International Decade of Natural
IASPEI Sub-commission on Earthquake Prediction works as fol­
Disaster Reduction (IDNDR).
lows. Nominations are submitted to the chairman of the Sub-
Placing a precursor, a method, or a case history on this List
commission (see "Call for Nominations", Boxes 1 and 5). The
does not guarantee that the reported anomaly was actually a
chairman, with the help from Sub-commission members, selects
genuine precursor, that the method works in general or that the
experts in the subject matter of the nomination for review by mail.
case history is without shortcoming. A method is included on the
The target number of anonymous mail reviews is four. A panel
List if the majority of the reviewers and panelists thought it more
convened by the chairman of the Sub-commission meets and
likely than not that the method may be useful for earthquake pred­
reviews the nomination and the mail reviews. The target number
iction. An individual case history is put on the List if the majority
thought that it was more likely than not that the claimed anomaly
was real and physically related to the mainshock. Similarly, the
decision by the panel not to place an item on this list does not Call for Nominations (February 1989)
necessarily mean that it concludes that there is no value in that
Researchers are invited to nominate outstanding examples
line of research. It only means that the majority of the reviewers
of geophysical precursors for inclusion in a list of potentially
and panelists thought that the work or the documentation was
reliable precursors which the Sub-commission is preparing.
incomplete or had shortcomings to a degree that makes it more
The purpose of preparing such a list is to come to a consensus
likely than not that the technique in its current state of develop­
on (a) the quality criteria which a case history has to meet to
ment is not yet established as useful for earthquake prediction.
be considered well substantiated, and (b) which case histories
Also we do not know at present to what extent precursors may be
are well substantiated. It is important to identify precursors as
different in different tectonic settings. A method that appears
either reliable or insufficiently well defined for testing physical
promising or useless in one environment may not be so in another.
models for the earthquake preparation process.
The Sub-commission and the evaluation panels feel that repro­
Researchers who propose a particular case for inclusion in
ducibility of experimental results is a very important criterion for
the list are assumed to be advocates of the case and are
acceptance of claims in natural sciences. However, in earthquake
expected to supply supporting evidence. The evidence should
studies reproducing an experiment is not easily done. Almost all
address the criteria detailed in the attached list. The ideal
of the nominated precursors are supported by a limited number of
nomination package consists of: (1) a summary defining the
sets of observations, often by only one investigator working in a
nomination and summarizing its strong and weak points, and
single tectonic setting. The experiments on which earthquake
explaining why this case or method should be included in the
prediction research is based depend on strong earthquakes occur­
list of significant precursors, (2) published papers on the case
ring near adequately instrumented sites. However, since we do not
history or method in question, and (3) unpublished detailed
know how to predict the location of the next strong earthquake,
supporting evidence (optional).
and because the occurrence of a strong earthquake at any one site
The facts and interpretations of each case will be reviewed
is rare, and because relevant conditions can never be controlled
by a working group of the Sub-commission with the help of
the way they are in the laboratory, decades are likely to pass
anonymous outside reviewers. The reviews, together with the
before rigorous verification of observational results can be
Sub-commission evaluation, will be transmitted to the advo­
achieved. The Sub-commission believes that it would be a disser­
cate. The advocate has the option of responding to specific
vice to earthquake prediction research to reject essentially all
objections or criticism, and of resubmitting the case with addi­
claims of significant precursors at this time because independent
tional information.
verification is lacking.
Documentation of the absence of a precursor near
The List presented here cannot be regarded as comprehensive,
mainshocks is also invited. In these cases, an explanation of
and there is a serious obstacle to making it comprehensive,
the circumstances whereby a precursor was expected is neces­
because important publications exist in languages other than
sary.
English or French, the two official languages of IUGG. These
The Sub-commission will not consider predictions of pend­
documents cannot be evaluated by international reviews through
ing earthquakes, only case histories of past events. Cases
the IASPEI Sub-commission. This is unfortunate because in some
under review will be discussed and the review process will be
of the countries with the largest earthquake prediction research
evaluated at the IASPEI Istanbul assembly.
efforts many such documents are produced.
Please send your nominations with six copies of all support­
It is expected that eventually the List will look different from
ing material to the chairman of the IASPEI Sub-commission
this preliminary list, because earthquake prediction research is in a
on Earthquake Prediction.
developing stage. Items may be included in the preliminary list
which may not be retained in the future List, unless improvements Boxl
in the data quality or analysis methods bring them up to the higher
1
Copyright American Geophysical Union
Special Publications Evaluation of Proposed Earthquake Precursors Vol. 32
2 INTRODUCTION
of panelists is seven. After discussion of the merits and shortcom­ ponents of precursors as well as critics would present their cases
ings the panel decides whether to accept the nomination for the to a panel of Sub-commission members. The product should be a
IASPEI List of Significant Precursors. If the nomination is not balanced report comparing the merits and shortcomings of the
accepted, specific reasons for the decision must be given. method evaluated.
The publication of the evaluations is made in reports issued
periodically by the Sub-commission. The items published for each Need. The need to evaluate precursors arises because now that
nomination are: (1) title and authorship together with the nomina­ the exploratory stage of earthquake prediction research is over,
tion text submitted by the author(s) and pertinent literature cita­ there seems to exist a great deal of difference in opinion on what
tions (if no nomination text was submitted the abstract of the key has been accomplished so far. At one end of the spectrum are
article submitted by the author(s) is published), (2) the panel opin­ those researchers who believe that hundreds of precursory
ions, (3) the reviews and (4) the author's reply. The authors have anomalies have been observed for a large variety of parameters.
the option to withdraw their nomination after the review process is At the other end of the spectrum are those scientists who believe
completed. that not a single precursor has been documented well enough to be
accepted. With the IDNDR coming up, IASPEI's Sub-
In the selection of panelists and reviewers it is important that
commission on Earthquake Prediction decided to evaluate claims
representatives from different nations are included such that dif­
for observed precursors.
ferent points of view of how to conduct earthquake prediction
research are considered. The countries from which experts have
been drawn so far include: Canada, China (Peoples Republic of), Definition of Precursor
Denmark, France, Germany, Great Britain, Greece, India, Italy,
A "precursor" is defined as a quantitatively measurable change
Japan, Mexico, New Zealand, Switzerland, Turkey, USA, and
in an environmental parameter that occurs before mainshocks,
USSR. The panel should be made up of a group of scientists who
and that is thought to be linked to the preparation process for
possess balanced expertise in several fields pertaining to earth­
this mainshock.
quake prediction research. Scientists with particularly strong
views concerning the authors or subject matter of the nomination Box 2
to be evaluated are not desirable for the panel. They may however
act as reviewers. Reviewers as well as panelists may be drawn In this evaluation process there are three objectives: (1) a Prel­
from the entire earth science community. Whenever possible, iminary List of Significant Precursors which will serve as an
members of the Sub-commission will be asked to serve as panel­ assessment of the current scientific capability of predicting earth­
ists. quakes, (2) a list of Validation Criteria (Box 3) which details the
The most serious problem with this evaluation task is that no requirements that an ideal case for a precursor should meet, and
funding is available to conduct it. Highly competent experts must (3) an assessment of the shortcomings of precursor research that
be found who are willing to donate their time as Sub-commission qualifies for the List in some people's opinion but not in others.
members, as reviewers and as panelists. This means that some­ Much would be achieved if the scientific community could reach
times it is difficult to get enough reviews together. To assemble a an approximate consensus on the Validation Criteria. It is recog­
highly qualified panel is even more difficult, since no travel funds nized that the ideal validation criteria are most likely impossible
are available. So far the occasions of scientific meetings were to reach by measurements made in the real world, especially with
used to hold panel meetings. For this reason the selection of panel the limitations imposed by real funding. Thus the Validation Cri­
members was restricted to those experts attending these meetings. teria published here are meant as the ideal to strive for, and they
This makes it difficult to reach a balanced representation of all are subject to improvement. Suggestions for changes in the cri­
subdisciplines and all countries with experts. Also the speedy teria are invited by the Sub-commission. Special Validation Cri­
progress of the evaluations is severely hindered by the restriction teria for separate research fields should perhaps be developed such
that panels can only meet at large and international conferences. that specific needs and issues can be addressed.
Not all needs of evaluation can be met by this review process.
For evaluating entire methods, especially if they are complicated, A Call for Nominations (Box 1) was issued by the Sub-
or for evaluating several proposed precursors to one extensively commission in February 1989, inviting the submission of research
studied mainshock, funds would be necessary to call an evaluation on precursors that could be evaluated by the Sub-commission.
meeting. Such a meeting could be envisioned as one at which pro­ This volume presents the results of these evaluations.
Copyright American Geophysical Union
Special Publications Evaluation of Proposed Earthquake Precursors Vol. 32
3
WYSS
Guidelines for Submission of Earthquake
Precursor Candidates
Validation criteria. Proposed precursors should satisfy the following criteria: (a) The observed anomaly should have a relation
to stress, strain, or some mechanism leading to earthquakes. Evidence of a relationship between the observed anomaly and the
mainshock should be presented, (b) The anomaly should be simultaneously observed on more than one instrument, or at more
than one site, (c) The amplitude of the observed anomaly should bear a relation to the distance from the eventual mainshock. If
negative observations exist closer to the mainshock hypocenter than to the positive observations, some independent evidence of
the sensitivity of the observation sites should be provided. For instance, if the anomaly is observed at a site that appears particu­
larly sensitive to precursory strain, it should also be more sensitive to tidal and other strains, (d) The ratio of the size (in time and
space) of the dangerous zone to the total region monitored shall be discussed to evaluate the usefulness of the method.
Data. Data submitted to support a candidate precursor must include the exact location of all relevant observation sites, the
time when the anomaly was observed, and the location, time, magnitude, and focal mechanism of the mainshock associated with
the precursor. Details of instrument installation and operating conditions shall be provided. Relevant records of environmental
conditions at recording sites such as temperature, atmospheric pressure, and rainfall shall be provided. There should be a per­
suasive demonstration that the calibration of the instrument is known and that the instrument is measuring a tectonic signal. This
might be done, for example, by comparing recordings of identical or related instruments installed close to each other. Reduced or
original data showing the claimed anomalies shall be provided in detail, including figures and tables. Original instrumental
recordings or copies of them shall be provided if requested. Data processing steps shall be explicitly explained. Such steps would
include removing signals due to installation, changes in instrument properties, and environmental conditions. The possibility of
errors introduced inadvertently during data gathering and analysis should be evaluated in detail. All data gaps should be
explained, and data editing criteria should be described in detail. It is necessary to provide a long-term record of data so that the
long-term signal and noise characteristics can be evaluated.
Anomaly detection. Anomaly definitions shall be precisely stated so that any other suitable data set can be evaluated for such
an anomaly. It should be shown how normal values of data during a time interval are established. The difference between
anomalous and normal values shall be expressed quantitatively, with an explicit discussion of noise sources and signal-to-noise
ratio. Negative evidence (such as failure to observe the anomaly at other sites nearer the earthquake hypocenter) should be
reported and discussed.
Association of anomalies with subsequent earthquakes. The rules and reasons for associating a given anomaly with a given
earthquake shall be stated precisely. The definition of an anomaly and the association rule should be derived from a data set other
than the one for which a precursory anomaly is claimed. Alternatively, a physical theory may be used to define an anomaly and
association rule. The probability of the "predicted" earthquake to occur by chance and to match up with the precursory anomaly
shall be evaluated. The frequency of false alarms (similar anomalies not followed by a mainshock) and of surprises (similar size
mainshocks not preceded by an anomaly) should be discussed. The possibility that anomalies are related to prior earthquakes
instead of future earthquakes should also be discussed. The size of any precursory anomalies should be compared with the size of
any coseismic anomaly, and the relative sizes should be explained. A complete listing of significant earthquakes near the record­
ing instrument is necessary so that possible association with other shocks can be assessed.
Box 3
Copyright American Geophysical Union
Special Publications Evaluation of Proposed Earthquake Precursors Vol. 32
4 INTRODUCTION
Results. In response to the first Call for Nominations (Box 1)
31 nominations were submitted. Three of these were withdrawn
by the authors before the evaluation procedure was completed. 40
Apparently some of the authors had not realized at first how
TYPE OF DATA
35
rigorous the review process is. Three additional entries were A total of 28 cases processed
withdrawn after the evaluation was negative. This is the preroga­
30
tive of the authors. One nomination could not be handled by this
review process because its evaluation would require an evaluation
25
meeting. The evaluations of the remaining 24 cases are detailed in
this volume (Figure 1). In this evaluation process 80 reviews 20 -
were received from 54 reviewers. The number of authors of the
nominations totaled 62, and 32 scientists served on 6 panels. 15 -
80
70 -
PROCESSING OF NOMINATIONS
60 -
31 nominations received
50 - FIG. 2. Among the 28 nominations reviewed those dealing with
crustal deformations (CRUST DEF) were the most numerous, fol­
40 - lowed by studies of seismicity patterns (SEIS PATTERN). Elec­
tromagnetic phenomena (E & M), seismic wave propagation
30 (SEIS WAVES). Geochemical changes (GEOCHEM) and
climatic changes (CLIMATE) were reported less often.
20
ous parameters were explored for their possible suitability for
10
earthquake prediction. Now this first exploratory stage appears to
be over, with critics demanding quantitative and rigorous analysis.
Li a way it may be unfair to measure relatively early research with
FIG. 1. Of the 31 nominations received the results of 24 were a yardstick of rigor recently developed. Nevertheless, this exer­
published in this report (REPORTED), three were withdrawn after cise is useful because it makes it clear in what specific aspects the
(WDRAWN AFT) and three before (WDRAWN BEF) the review research methods need improvement. It may well be that some of
process. In one case the IASPEI Sub-Commission did not have the old data sets, or some of the old ideas and methods, could be
the resources for a review (UNABLE). placed on the List, if they were re-analyzed or re-formulated to
meet the requirements now perceived as necessary (see Validation
Grouping the nominations by discipline, one finds that the larg­ Criteria).
est number of entries deal with crustal deformations, although
several different methods are used for measuring these (Figure 2).
The papers dealing with seismicity patterns of one kind or another
were the next numerous group, followed by the papers addressing
electromagnetic phenomena and seismic wave propagation pro­
perties. One entry each came from the fields and methods of geo­
chemistry and climate changes. Several fields and methods of
earthquake prediction research were not yet represented in this
first group of nominations.
Of the 28 nominations processed, only three were accepted for
the Preliminary List of Significant Precursors (Figure 3). For five
entries no decision was reached. In these cases it was thought that
additional information existed, and that these cases might qualify
for the List if they were presented in full. The remaining 20 cases
were not accepted for the List. Some nominations that deal with
the same earthquake or the same method have been treated jointly
in one case. No nomination was received for an outstanding case
in which a precursor failed to be observed in spite of excellent Preliminary No decision Not accepted Negative
data (negative in Figure 3). FIG. 3. The result of the evaluation process was that from 28
One of the chief reasons why most nominations were not nominations three were accepted for the Preliminary List of
accepted at this time may have been that earthquake prediction Significant Precursors (PRELIMINARY), for five no decision was
research is at a new stage in its development. The overwhelming made (NO DECISION) and 20 were not accepted (NOT
majority of the nominations were research papers without addi­ ACCEPTED). No nominations were received reporting negative
tional explanations, published some years ago at a time when vari- results discounting a precursor method (NEGATIVE).
Copyright American Geophysical Union
Special Publications Evaluation of Proposed Earthquake Precursors Vol. 32
WYSS 5
The two shortcomings most commonly cited by the panel and the precursor could be used in actual predictions (Figure 4). How­
the reviewers are a lack of clear definition of what constitutes a ever, these might not be fatal criticisms, if other aspects of the
precursory anomaly, and a lack of statistical tests by which the work were outstanding. And finally the length of the observation
significance of the proposed anomaly was measured (Figure 4). period, especially during background time, was seen as too short
Most authors seemed to rely on the reader to figure out what the in some cases. Only time and steady research funding can remedy
anomaly was, when it started and whether it was significant. As a this problem.
consequence the existence of the proposed anomaly is often in the There is a difference between accepting an article for publica­
realm of interpretation, when it should be a known fact (i.e., tion in a journal and accepting it for the List of Significant Precur­
amplitude, duration and significance level should be known, not sors. Work that shows a new observation, formulates the
debated). These two frequent shortcomings can be remedied in all hypothesis that this may be a precursor, and offers speculations
cases without additional instruments, data or earthquakes. about the physical process causing it may make an excellent arti­
The lack of details concerning the observations and analysis cle. However, it would be premature to include this type of work
techniques was also criticized in more than half the cases, and in in the List. The ideal case for the List would be a precursor which
about one third of the cases more details on instrumentation were has been quantitatively measured many times and which had been
requested (Figure 4). This is understandable and not the fault of tested repeatedly. A successful test would be one in which
the authors. All journal editors emphasize succinctness and mainshocks (that occurred previously or future ones) are success­
demand that articles be shortened to the greatest extent possible. fully predicted by algorithm, without generating too many false
However, in order to place a precursor on the List the panelists alarms.
and reviewers must be fully convinced of its usefulness. How can The results of this evaluation survey show that earthquake
they be, without full and detailed information on all aspects of the prediction research still has a long way to go to become useful.
experiment, the data and the method used? Thus it is now clear Only three cases were accepted for the Preliminary List, and all of
that nominators should furnish in their nomination material all the these with many caveats. In the work by Matsu'ura (case 1) only
detail they are not allowed to put into their articles. These aftershocks are predicted and this has not been done yet in real
shortcomings can be remedied without additional instruments, time. In the correct prediction of the Haicheng earthquake based
data or earthquakes. on fore-shocks reported by Wu et al. (case 2) many false alarms
The lack of exploring the possibility of other explanations of existed, but the false alarm rate has not been evaluated and no
the proposed anomaly and the lack of investigating the rate of methods exist to recognize fore-shocks in real time. In the case of
false alarms were also criticized frequently (Figure 4). Additional ground water anomalies (Wakita et al., case 3) also many ques­
analysis would probably be required for answering these ques­ tions remain, especially questions concerning the physical
tions. However, no additional data gathering would be necessary. mechanism. Thus, at this time, we have not a single method on the
In some cases the physical model proposed as explanation was List which could be said to be accepted universally and by which
criticized as unconvincing, and in other cases it was not clear how earthquakes can be predicted reliably.
The stage of development in the different fields of study is dif­
ferent. Several nominations dealing with crustal deformations
70 seem to have data that the reviewers wanted to believe, but the
SHORTCOMINGS lack of complete and rigorous analysis prevented the inclusion of
60 in 24 nominations published these nominations on the List. In the cases presented here there
seems to be no evidence for active research on how to make an
50 outstanding case for the existence of crustal deformation precur­
sors. In contrast the entries on wave propagation properties were
40
vigorously and well presented. In these cases the critics have also
given a great deal of thought to the problems of measuring the
30
claimed effects, and they also voiced their objections at elevated
technical levels. This vigorous debate in the area of wave propa­
20
gation precursors is apparently improving the methods and
knowledge, possibly to the point where these methods will
10
become accepted.
It is clear that a proposed method to predict earthquakes that is
Define Statist Detail Other exp Instru False al Model AppUcat Period
not put on the List is not judged as being useless. It only means
FIG. 4. The shortcomings most often cited by the panel were a that in the judgement of several reviewers and panelists the
lack of a precise anomaly definition (DEF) and of statistical method has not yet matured enough to be entirely convincing. In
evaluation of the anomaly significance (STATIST), followed fact one purpose of this evaluation procedure is to stimulate the
closely by lack of detail concerning the experiment (DETAIL) debate of how to improve earthquake prediction methods. It is
and lack of discussion of other possible sources for the claimed hoped that out of the dialog (nomination-criticism-author reply)
anomalies (OTHER EXP). Not enough information about instru­ would develop a sharpening of the criticized method that would
ments used (INSTRU), lack of evaluation of false alarm rates lead to its inclusion in the List.
(FALSE AL) and unconvincing physical models (MODEL) also The definition of "earthquake prediction" is also something that
were frequent problems. Finally the application of the proposed the IASPEI Sub-commission should develop. This definition may
precursor to a real prediction (APPLICAT) and the short duration be modified and improved as time goes on. Currently the
of the data period (PERIOD) were often cited as shortcomings. definition proposed is
Copyright American Geophysical Union