Evaluation for Short-Term and Annual Prediction of Earthquakes (ESTAPE)

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Despite the present-day controversy surrounding prediction research, both earthquakes and their predictions continue to take place. The need to use relevant information on these sudden, large disasters is increasingly urgent. The United Nations Global Programme for the Integration of Public Administration and the Science of Disasters (UNGP-IPASD) has developed an approach to evaluate short-term and annual forecasts of earthquakes. This approach can be used by public administrators, scientists, as well as by the general public to assess the effectiveness and reliability of forecasting reports.  

ESTAPE Equations

In developing ESTAPE, the UN Global Programme – IPASD tapped the practical experience gained over decades of observation and analysis, of Chinese earthquake prediction experts, members of the Special Committee for Natural Disaster Forecasting of the Chinese Geophysical Society. For more than three decades, these scientists have conducted their prediction research under a national policy that is supportive of earthquake forecasting. ESTAPE takes into account the unpublished standards for earthquake prediction outlined by the State Seismological Bureau of China in the early 1990s.

The phrase "earthquake prediction" refers to a forecast of a possible seismic event. ESTAPE focuses on the difference between the predicted and actual values of the three elements used to identify an earthquake event, i.e. time, location and magnitude. A typical prediction usually includes the ranges of the three elements, that is the ranges in magnitude M, origin time T, and location of the event R (geographic latitude and longitude). The mid-value of each range is M_o, T_o and R_o.

Based on analyses of empirical data recorded using different monitoring techniques and extensive discussion among the above mentioned scientists, score charts were developed to evaluate short-term and annual earthquake predictions. Earthquakes of three magnitude ranges are grouped and denoted by the subscript, j, where:

j=1	Ms = 5.0 to 5.9
j=2	Ms = 6.0 to 6.9
j=3	Ms = 7.0 to 8.0

Evaluation of each prediction element is determined as a function of the misfit in each element. For example, the index P_mj  for evaluating magnitude accuracy (denoted by subscript "_m") of earthquake prediction in the magnitude range group " _j"  is:

                        P_mj= a_0mj+ a_1mj (M_s- M_o) + a_2mj ( M_s- M_o)²         [1]

where the coefficients a_imj are least-square fits for empirical data collected over years for earthquake prediction work.

Similarly, evaluation indices for location and time are represented by P_rj and P_tj (with distinct sets of coefficients a_irj and a_itj for short term and annual predictions).

Prediction experts generally agree that the location element, r, is the most difficult to determine.  The composite evaluation index (P_j ) can then be expressed as a linear combination of the three evaluation indices, with unequal weights or difficulty factors of 0.3 to 0.4:

                               P_j = 0.3 P_mj + 0.3 P_tj + 0.4 P_rj                         [2]

By experience, when P>60%, the prediction can be regarded as socially useful.

Coefficient Tables

 P_mj  Magnitude Evaluation - short term prediction (ESTAPE-S)

j	a0mj	a1mj	a2mj
1 (Ms= 5.0 to 5.9)	100	-40.201030	-20.571300
2 (Ms= 6.0 to 6.9)	100	-46.229370	1.144796
3 (Ms= 7.0 to 8.0)	100	-34.751970	-0.377080

  P_tj  Time Evaluation - short term prediction (ESTAPE-S)

j	a0tj	a1tj	a2tj
1 (Ms= 5.0 to 5.9)	100	-1.703704	0.012226
2 (Ms= 6.0 to 6.9)	100	-1.126485	0.004194
3 (Ms= 7.0 to 8.0)	100	-0.870684	0.002612

P_rj  Location Evaluation - short term prediction (ESTAPE-S)

j	a0rj	a1rj	a2rj
1 (Ms= 5.0 to 5.9)	100	-0.313671	0.000355
2 (Ms= 6.0 to 6.9)	100	-0.211015	0.000147
3 (Ms= 7.0 to 8.0)	100	-0.131746	0.000047

    P_mj  Magnitude Evaluation - annual prediction (ESTAPE-A)

j	a0mj	a1mj	a2mj
1 (Ms= 5.0 to 5.9)	100	-50.000420	0.000401
2 (Ms= 6.0 to 6.9)	100	-38.511110	-0.516723
3 (Ms= 7.0 to 8.0)	100	-33.333220	-0.000101

  P_tj  Time Evaluation - annual prediction (ESTAPE-A)

j	a0tj	a1tj	a2tj
1 (Ms= 5.0 to 5.9)	100	-19.999940	-0.000007
2 (Ms= 6.0 to 6.9)	100	-19.999940	-0.000007
3 (Ms= 7.0 to 8.0)	100	-19.999940	-0.000007

  P_rj  Location Evaluation - annual prediction (ESTAPE-A)

j	a0rj	a1rj	a2rj
1 (Ms= 5.0 to 5.9)	100	-0.259285	0.000206
2 (Ms= 6.0 to 6.9)	100	-0.189352	0.000109
3 (Ms= 7.0 to 8.0)	100	-0.115339	0.000039

Reference

Chu, J. J. and Col, J. M., Evaluation for Short Term and Annual Prediction of Earthquakes (ESTAPE), in Manual on the Forecasting of Natural Disasters: Geomagnetic Methods, prepared for the UN International Workshop on Geomagnetic Methods, sponsored by UN Dept. of Econ. and Soc. Affairs, New York, NY, and UN Dev. Prog. Beijing, February 12-18,1998.

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