Introduction.—The occasion for publishing this catalogue of Philippine earthquakes which were of violent and destructive character has been furnished by a request from Prof. John Milne for a list of such phenomena, to be included in the General Earthquake Catalogue which this eminent seismologist is preparing under the auspices of the British Association for the Advancement of Science. The said general catalogue has been undertaken with a view toward reducing to uniformity and completing those published years ago by Robert Mallet (1859) and Perrey (1844-1871). The form adopted for Professor Milne's new catalogue is very concise, comprising only the date, intensity, and region together with principal localities affected. It will contain only the earthquakes of intensities VII to X according to the scale of De Rossi-Forel, and these will be divided into three classes: Class I will be formed by the earthquakes of sufficient force to produce cracks in buildings and to throw down chimneys; they correspond to force VII of De Rossi-Forel. Class II consists of the earthquakes which not only threw down chimneys but also walls and some weak structures; force VIII of De Rossi-Forel. Class III comprises the earthquakes which caused general destruction; force IX and X of De Rossi-Forel. As this classification is as purely conventional as every other and adopted only in the catalogue mentioned, we do not employ it in the present catalogue of Philippine earthquakes, but retain the almost universally adopted scale of De Rossi-Forel. We shall also present more details as to the towns and buildings damaged, the number of victims and other disastrous effects than enter into the catalogue of Professor Milne.
Hence, the differences between the list prepared for Professor Milne as well as the partial catalogue published in our Monthly Bulletin for February of the present year consist in the following: (1) This catalogue contains also several earthquakes whose intensities were between VI and VII, while in the former only such figure as according to their effects were decidedly of force VII. (2) The new catalogue is more complete as to details concerning the towns, etc., which have been destroyed.
It is to be regretted that we are unable to present here a complete historical catalogue of all the destruction wrought in the Archipelago by earthquakes since the time when Legaspi and Urdaneta first set foot on these shores. But the old chroniclers, who dwell upon the political happenings with an attention to detail which is occasionally overdone, were invariably laconic when there was question of earthquakes and similar natural phenomena; as a rule they were satisfied with mentioning the occurrence in a general and therefore vague way, without any attempt at precision as to dates and places. Still the writers in the Philippines did nothing worse than imitate their colleagues throughout the rest of the world. This fact is responsible for the great contrast exhibited by our catalogue as regards the number and details of earthquakes which occurred prior to 1800, records of which have been preserved, and the same data for the period from 1800 to the present time. This same difference is observable in all catalogues of a similar nature, even in those which cover phenomena which occurred in Europe. As to the Philippine writers, an additional excuse is found in the peculiar conditions of life in these Islands. As far as we know, only two earthquakes which took place during the period which alone can come under consideration—that is, since the discovery of the Archipelago—have claimed a considerable number of victims, and these in the capital, because outside of Manila—if we except two or three of the principal cities—the buildings which could become dangerous during an earthquake have always been few.
Moreover, in a country in which fires consume every year thousands of dwellings and where the terrible typhoons frequently destroy whole towns with heavy loss of lives, the damage done by earthquakes has rarely been so great as to impress those occurrences indelibly upon the memory. This is beyond doubt one of the reasons why prior to the beginning of the nineteenth century hardly any data can be found concerning the numerous earthquakes which during the preceding two centuries must have occurred in the Visayas and above all on the large Island of Mindanao.
The first earthquake of which the chronicles contain a mention is that of 1599. There is no reasonable doubt that during the twenty-eight years which had then elapsed since the founding of Manila by Legaspi, several strong and possibly even destructive earthquakes occurred in this part of Luzon Island, but, as the author of the "Verdadera relación de la grande destrucción * * * del año 1645" tells us, "when first founded, Manila consisted of wooden houses roofed with a certain kind of palm leaves, the same which the natives use in their buildings." Hence the damage done by these earthquakes must have been insignificant. Much more terrible were the losses caused by conflagrations which within a few years twice wiped out the entire city.
The first Bishop of Manila, Domingo de Salazar, seeing the city exposed to such general destructions by fire like the one of February 14, 1583, gave the first impulse to the construction of stone buildings and worked indefatigably in this direction. In person he explored the surroundings of Manila in quest of stone quarries and by the middle of the year 1591 he had nearly finished his palace and the cathedral, when financial difficulties caused a temporary suspension of the work. At the same time a great number of public and private buildings were under construction. The enthusiasm for structures of stone or brick with tile roofs did not diminish during the next fifty years. The chroniclers tell us that "the Spaniards began to build their houses of stone and tiles without the so necessary precautions against earthquakes. * * * Beautiful structures and dwelling houses were reared, so high and spacious that they resembled palaces; magnificent churches with lofty and graceful towers, within the walls of Manila as well as outside of them: all of which made the city very beautiful and gay and contributed equally to health and pleasure." The disaster of 1645, commonly called the earthquake of St. Andrew, as it occurred on the feast of this apostle, November 30, razed nearly every one of these buildings to the ground, and since then the style and appearance of buildings has changed greatly throughout the Archipelago, with a correspondingly great saving of lives in the subsequent earthquakes.
Masonry arches were henceforth banished from the churches; the heavy walls of the latter were further strengthened by massive buttresses; and the towers were given truly enormous substructures. But even with these precautions there is at present hardly one out of the hundreds of churches built during the seventeenth and eighteenth centuries which did not some time or other require important repairs of its masonry work or even partial reconstruction owing to earthquake damages. The only structure of this class which thus far has withstood all convulsions, is the church of St. Agustin, Manila. Nevertheless, as we have stated before, the chroniclers hardly mention all this destruction, except in a very general and cursory manner. I do not hesitate to say: they were accustomed to see similar havoc created nearly every year in one part of the Archipelago or the other by some severe typhoon, accompanied by far greater loss of lives and property, and consequently much more felt by the people than the destruction of a church, convento, municipal building ("tribunal"), one or two bridges, or other masonry structure.
In the present catalogue our aim has been to present all that is known of the various violent and destructive earthquakes on record. The first column of each page contains the ordinal number of the disturbance for purposes of reference. In the second, the date is given as accurately as it could be ascertained, Roman numerals being used to designate the months. Unfortunately, of some earthquakes only the year is known; of others, the year and month. Of one (No. 32) the approximate hour has been recorded, but not the day of the month; while of another (No. 38) the hour has been preserved for posterity, but whether the phenomenon occurred during February or March, the records leave undecided. In the third column will be found, in the first place, the intensity of the disturbance, Roman numerals representing the degrees of the scale of De Rossi-Forel (I-X); then the region affected most, and finally the damages caused, if known, and other information, if available.
In describing the epicentral regions, the present distribution of the Archipelago into provinces has been used throughout the catalogue. This division is shown on the first of the two maps of the Philippines which accompany this catalogue (Plate I). As to the designation "Benguet" occasionally occurring in the text where provinces are enumerated, but not found on the map, we beg to offer the excuse that the region thus named is exceedingly well known in the Philippines as it contains Baguio, the health resort of the Islands. For the readers outside of the Archipelago we remark that Benguet is at present a subprovince of the Mountain Province, of which it forms the southernmost part. The location of Baguio is shown on the map on Plate II. A similar remark applies to Lepanto and Bontoc, likewise divisions of the Mountain Province, whose capitals, Cervantes and Bontoc, are indicated on the same map.
As we would hardly be justified in assuming that every reader is in possession of a detailed map of the Philippines, and a knowledge of the general distribution and the main directions of the principal mountain systems of an earthquake country is important, we add a second map on which these data are shown by means of dashes, together with the most important seismic regions, and the positions of the principal towns, bays, etc., mentioned in the text. (Plate II.)