Seismicity Of The Philippines And The Expectations Of Maximum Earthquake Motions

Rolu P. Encarnacion

The study of the seismicity of a certain locality has always been the obsession of many earthquake scientists, since seismicity is the general view of the frequency of earthquakes in a certain place during a certain period. This research paper deals with the Philippine seismic activities for the period 1901 to 1974. With the aid of the basic equation of the Gutenberg-Richter's statistical relation and a modification of this relation by Peter Welkner, 6-value had been determined and subsequently, a-value, which is regarded as the index of the mean annual seismic activity, was also computed for the area of study correspondingly.

Nevertheless, the highlight of this report is on the estimation of expected maximum earthquake motions, that is; the particle velocity at the base rock and the acceleration on the ground at their extreme values for some return periods. For the maximum velocity calculations, Kanai's attenuation model was used and for the maximum acceleration, the average of McGuire and Oliveira's attenuation models were considered. In this aspect, the author utilized computer programs in the analysis and calculation schemes. There were 19 selected sites of the country which were run through the computer program and yielded results favorably in accordance with Philippine seismicity. The importance of these results lies on the fact that it projects a probability of occurrence of at least some destructive tremors during a specific time interval. In seismological point of view, this probability is better known as the earthquake risk over a specified location and on a certain period of time. Furthermore, the probability value will be very useful in the field of Earthquake Engineering.

A Probable Correlation Between 500-Mb Vorticity Advection And Large-Scale Precipitation

Bernardo M. Soriano, Jr.

In this study, the technique of determining a statistical relationship between a desired meteorological element and parameters from a dynamical model at some projection time was applied to predict precipitation amounts associated with large-scale atmospheric phenomena at three forecast intervals. The 500-mb vorticity advection, which is one of the output parameters of the Barotropic Model developed by the Department of Meteorology and Oceanography, University of the Philippines, was used as predictor in this technique called Model Output Statistics (MOS).

Regional and general simple regression equations were derived on two different grid networks over the Philippines after intermediate preparation of limited available data. This indicated a higher correlation between the variables in the finer grid mesh where curvilinear equations were then obtained. Tests of significance on correlation coefficients favored the non-linear formulas. However, generalized equations of both sets of formula did not have significant difference.

Experiments on ten independent tropical cyclone cases revealed that the curvilinear equations yield generally closer regional estimates over the three forecast intervals. However, predictions were underestimated. The discrepancy of the estimates was attributed to the preponderance of less significant vorticity advection values in the curvilinear formulas. In view of the small diference between the predictions of the two sets of equation and due to the higher significance of the correlation in the curvilinear equations, the use of the last set of formulas was preferred.

Relationships Among The Meteorological Parameters Observed On Board R/v Researcher And R/v Albacora

Emma A. Vergara, Araceli L. Fontano, Cynthia A. Pajadan

The study aimed to monitor the weather conditions in the open oceans within the Philippine area of responsibility, with particular interest on the state of the sea. The variables ranging from 24 to 27 were used in a stepwise-regression analysis. The technique had offered a fairly reasonable forecasting tool as an alternative due to the lack of any study on parameters like wind waves and swells. In cases where only the wind speed value (FF) would be available, the height of the swell (SHGT) could be roughly expressed as:

SHGT = -0.0221 + 0.3046 FF

The height of the wind waves (WHGT) at a given day (YY) and wind speed (FF) could be estimated in the form:

WHGT = 2.7 - 0.113 YY + 0.147 FF 

Beyond these preliminary findings, no clear-cut conclusions could be made due to the constraints imposed by the limited observations. It would be worthwhile to consider extending the data input in terms of time and area coverage, in future studies.