Future Strong Earthquakes Research Articles

Bursts of seismicity as long‐term precursors of strong earthquakes

One or more earthquakes with abnormally large numbers of aftershocks at the beginning of their aftershock sequences are possible long‐term precursors of a stronger earthquake. This precursor, named pattern B (bursts of aftershocks), was tested together with two other possible premonitory patterns, S and Σ, described previously. Pattern S (swarm) consists of the spatial clustering of earthquakes at a time when the seismicity of the region is above average. Pattern Σ consists of an increase in the sum of earthquake energies to the 2/3 (roughly) power, in a sliding time window. These three patterns were tested by retrospective long‐term prediction of earthquakes of Southern California, 1932–1977, with magnitudes ≥6.5. The total duration of identified periods of elevated probability of occurrence is about 14 years. Five out of six earthquakes occurred during these intervals. However, the patterns do not indicate the exact location of future strong earthquakes within the region. All three patterns seem to represent different projections of the same general pattern, of ‘bursts of seismicity,’ i.e., an abnormal clustering of earthquakes in the time‐space‐energy domain. Pattern B also precedes strong earthquakes in New Zealand and Italy; Pattern Σ precedes strong earthquakes in New Zealand.

Strategies for strong motion earthquake recording in New Zealand

The problem of how to record future strong earthquakes in New Zealand is examined by considering what data is required, how effective the present network will be in gathering that data, and what new technology is now available. It is concluded that present methods result in an unsatisfactory use of funds. There is a current emphasis on frequent expert servicing which, while it leads to a high probability of any recorder operating, restricts the number of installations able to be serviced. Thus we have a high probability of any given recorder working, coupled with a small probability of any given earthquake being within range of a recorder. The suggested future strategy is to first develop a new accelerograph of high reliability and the capability of self testing. This would incorporate a non volatile no moving parts electronic memory. Servicing of this would be at infrequent intervals, but a program of reporting the self test results by postcard would be adopted. By thus cutting down on recorder servicing and record processing times, we could force the major factor to be capital cost, and thus allow the network to expand until a realistic probability of recording a major earthquake was reached. The installation of about 70 additional strong motion accelerographs in the main seismic region would allow a good chance of recording our next major earthquake.