{
  "id": "focos-sismicos-del-archipielago-filipino-1900",
  "type": "entity",
  "name": "Focos seismicos del Archipielago Filipino (1900): the Manila Observatory's seismic zonation of the Philippines",
  "summary": "A treatise printed in 1900 by the Jesuits of the Manila Observatory that divides the Philippines into three seismic zones by parallels of latitude, names the epicentral foci in each, tabulates their tremors, and prints a colour map of them. It reasons from Lyell and Lapparent, defines epicentre as the \"foco aparente\", and reaches across the Pacific for its example of an earthquake that arrived in complete silence: Riobamba, 4 February 1797.",
  "locale": "en",
  "tags": [
    "philippines",
    "science",
    "seismology",
    "geology",
    "jesuits",
    "nineteenth-century",
    "cartography",
    "institutions"
  ],
  "relations": [
    {
      "rel": "related",
      "target": "observatorio-meteorologico-de-manila"
    },
    {
      "rel": "related",
      "target": "colonial-records-as-a-climate-archive"
    },
    {
      "rel": "related",
      "target": "buenaventura-suarez-astronomo-de-san-cosme"
    }
  ],
  "questions": [
    "When were the Philippines first divided into seismic zones?",
    "What did the Manila Observatory's seismic department do?",
    "How did nineteenth-century Spanish seismologists define an epicentre?",
    "What was the earliest seismic map of the Philippines?",
    "How did colonial observatories in Asia and America share earthquake evidence?"
  ],
  "claims": [
    {
      "id": "c1",
      "text": "Where the treatise sits and how it was read. \"Tratado XI - Focos seismicos\" occupies pages 269 onward of tomo II of \"El archipielago filipino\", Washington, Imprenta del Gobierno, 1900, compiled by the Jesuit fathers of the Manila Observatory. It was read here as page scans of the original imprint. Its general chapter and its index were read; the regional catalogues of tremors were not read page by page, and the pid for the prologue page returns the plate rather than the text, so the prologue itself was not opened.",
      "sources": [
        "algue-archipielago-filipino-1900-tomo-ii"
      ],
      "confidence": 0.9
    },
    {
      "id": "c2",
      "text": "The treatise opens with a folded colour plate headed \"FOCOS SEISMICOS DEL ARCHIPIELAGO\", a map of Luzon and the Visayas ruled in degrees from 119 to 123 east and 10 to 19 north, on which the principal foci are marked by numbered stars I to IV with lines radiating from each and the surrounding country shaded in graded reds. It is a seismicity map, not a map of individual earthquakes: the shading is the zone of effect, drawn as an area.",
      "sources": [
        "algue-archipielago-filipino-1900-tomo-ii"
      ],
      "confidence": 0.8
    },
    {
      "id": "c3",
      "text": "Its definitions are worth quoting because they are the working vocabulary of the discipline in Spanish in 1900. A seismic focus is \"el punto, o por mejor decir, la porcion de masa interna del globo terraqueo puesta en conmocion por fuerzas plutonicas, quimicas o puramente mecanicas\", whose movements are transmitted to the surface by the laws of propagation, producing tremors or earthquakes according as the intensity is lesser or greater. The epicentre, \"llamado tambien foco aparente\", is the point of the surface toward which the commotions from the real or centric focus are directed and where they are felt before anywhere else.",
      "sources": [
        "algue-archipielago-filipino-1900-tomo-ii"
      ],
      "confidence": 0.9
    },
    {
      "id": "c4",
      "text": "It distinguishes partial from general foci, and the reasoning is the reason the map is drawn as areas. Seismologists and geologists attend by preference to the real focus and epicentre of each disturbance; but where a region is frequently shaken and the epicentres do not coincide in one point, appearing now in one and now in another part of the agitated zone, one may consider in the depths of the earth a more or less considerable space of seismic activity to which all the partial epicentres may be referred, and consequently a common epicentre.",
      "sources": [
        "algue-archipielago-filipino-1900-tomo-ii"
      ],
      "confidence": 0.85
    },
    {
      "id": "c5",
      "text": "Submarine foci and sea waves are treated as the same phenomenon reaching water, with shipboard evidence for it. Earthquakes felt at sea produce in ships an effect like a shock against rocks or the bottom, \"como se experimento en el temblor ocurrido el ano 1835, a lo largo de la costa de Chile, donde los buques, quier anclados quier navegando, sintieron algunas sacudidas como si hubiesen tropezado con algunas rocas\", and as the steamer Brutus experienced at the Zamboanga tremors of September 1897. Where the depth forbids supposing the ship has grounded, the treatise concludes, a submarine seismic phenomenon may be inferred on solid grounds.",
      "sources": [
        "algue-archipielago-filipino-1900-tomo-ii"
      ],
      "confidence": 0.85
    },
    {
      "id": "c6",
      "text": "On subterranean noises the treatise reaches across the Pacific for its counter-example, which is how a Manila observatory ends up citing Spanish America. Such noises bear no proportion to the violence of the tremors and are not manifested alike in all latitudes: \"casos ha habido de terremotos verdaderamente destructores en que ha reinado el mas completo silencio, como en el famoso de Riobamba del 4 de Febrero de 1797\", while in other cases great subterranean noises have been followed by no commotion at all. It adds that the noises are heard most in volcanic regions, and leaves open whether that is because volcanism gives more body to the vibrations or because near volcanoes the phenomena develop at a lesser depth.",
      "sources": [
        "algue-archipielago-filipino-1900-tomo-ii"
      ],
      "confidence": 0.85
    },
    {
      "id": "c7",
      "text": "It also defines the seismic period, a unit of description rather than of instrument. When a focus displays greater activity, translated into a series of commotions all from one origin, these constitute what has properly been called a seismic period; ordinarily it begins with a shock of some intensity that weakens little by little until extinguished, though sometimes it is announced by slight oscillations that increase to a maximum, in which case the period has two pronounced phases, one ascending and one descending.",
      "sources": [
        "algue-archipielago-filipino-1900-tomo-ii"
      ],
      "confidence": 0.85
    },
    {
      "id": "c8",
      "text": "The zonation is the treatise's organising claim. \"Para mayor claridad en el estudio de los temblores que en Filipinas se van sintiendo, considera nuestro Observatorio dividido este Archipielago en tres grandes zonas seismicas, llamadas septentrional, central y meridional.\" The meridional is bounded by the parallels 5 degrees 9 minutes and 10 degrees north; the central by 10 degrees and 15 degrees 30 minutes north; the septentrional by 15 degrees 30 minutes and 21 degrees 3 minutes north. The first figure of the southern bound is indistinct in the scan read, which is why this claim is not carried higher.",
      "sources": [
        "algue-archipielago-filipino-1900-tomo-ii"
      ],
      "confidence": 0.75
    },
    {
      "id": "c9",
      "text": "Each zone is then filled with named foci. In the meridional zone fall the four foci of Mindanao; in the central, the two volcanic-seismic foci of Taal and Mayon south of Luzon; in the septentrional, the focus toward the north-west of that island, that of the centre and that of the north-east - besides other secondary ones. The index shows what each regional chapter carries: an epicentral region, a statistics of tremors, tables, and dated events, among them the Surigao earthquake of 1 July 1879 with \"cien temblores en veintiun dias\", the Pangasinan earthquakes of March 1892, the Cotabato earthquakes of 1871 and the appearance of the volcano of Camiguin del Sur in 1871.",
      "sources": [
        "algue-archipielago-filipino-1900-tomo-ii"
      ],
      "confidence": 0.8
    },
    {
      "id": "c10",
      "text": "The treatise argues inside the European geology of its day and says so in its footnotes, citing Lyell's \"Principes de Geologie\", chapter xxxii, for the hypothesis that one and the same cause produces earthquakes and the phenomena of volcanism - a hypothesis it judges \"no esta tan destituida de fundamento\" - and A. de Lapparent's \"Traite de Geologie\", page 445, for the appearing and disappearing island of Julia between Sicily and Pantelleria in 1831 and 1863. It is a provincial observatory reading the metropolitan literature and answering it with local observation.",
      "sources": [
        "algue-archipielago-filipino-1900-tomo-ii"
      ],
      "confidence": 0.85
    },
    {
      "id": "c11",
      "text": "The seismic department was late and physical. The same volume states that the seismic, magnetic and astronomical departments, provided with good collections of direct and recording apparatus, were created many years after the observatory's foundation of 1865, when its growth brought it staff and means; and it prints a photographic plate, \"Vista IV - Departamento seismico y torre de los aparatos meteorologicos, Observatorio de Manila\", showing the building with its instrument tower and storm-signal ball.",
      "sources": [
        "algue-archipielago-filipino-1900-tomo-ii"
      ],
      "confidence": 0.85
    },
    {
      "id": "c12",
      "text": "What this object rests on, and what it does not. It rests on the general chapter, the index and one plate of a treatise whose bulk is regional catalogues that were not read; the counts of tremors attributed to those chapters here come from the index headings, not from the tables themselves. The treatise is also the observatory describing its own work, and no independent seismological source was opened against it, so no claim here should be read as an assessment of whether the three zones or the numbered foci stand up to later work. What is claimed is what the 1900 imprint prints.",
      "sources": [
        "algue-archipielago-filipino-1900-tomo-ii"
      ],
      "confidence": 0.9
    }
  ],
  "takeaways": [],
  "faqs": [],
  "evidence_tier": "primary",
  "evidence": {
    "level": "industry_observation",
    "source_types": [
      "paper"
    ]
  },
  "moat_flag": false,
  "winning_edge": "Histories of seismology in Asia usually start with the Japanese instrumental work of the 1880s, and the Spanish Jesuit seismology of the Philippines survives in English mostly as a citation to Saderra Maso's later English-language catalogue under American rule. This object goes to the Spanish text of 1900 itself and gives what it says: the definitions of focus, epicentre and seismic period in the words used; the argument from partial to common epicentres that justifies mapping seismicity as shaded areas rather than as points; the three zones with their parallels and the foci assigned to each; the shipboard evidence for submarine foci from the Chilean coast in 1835 and the steamer Brutus at Zamboanga in 1897; and the Riobamba earthquake of 1797 cited from the other side of the Pacific as the case of a destructive earthquake that arrived in complete silence. It also states plainly which parts of the treatise were not read and that the witness is the institution describing itself.",
  "confidence": 0.8,
  "last_verified": "2026-08-14",
  "canonical_url": "https://hispanic-legacy.com/k/focos-sismicos-del-archipielago-filipino-1900",
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  "jsonld": {
    "@context": "https://schema.org",
    "name": "Focos seismicos del Archipielago Filipino (1900): the Manila Observatory's seismic zonation of the Philippines",
    "description": "A treatise printed in 1900 by the Jesuits of the Manila Observatory that divides the Philippines into three seismic zones by parallels of latitude, names the epicentral foci in each, tabulates their tremors, and prints a colour map of them. It reasons from Lyell and Lapparent, defines epicentre as the \"foco aparente\", and reaches across the Pacific for its example of an earthquake that arrived in complete silence: Riobamba, 4 February 1797.",
    "url": "https://hispanic-legacy.com/k/focos-sismicos-del-archipielago-filipino-1900",
    "license": "https://spdx.org/licenses/CC-BY-4.0.html",
    "dateModified": "2026-08-14",
    "citation": [
      {
        "@type": "CreativeWork",
        "name": "El archipielago filipino: coleccion de datos geograficos, estadisticos, cronologicos y cientificos - tomo II (Climatologia, Focos seismicos, Magnetismo terrestre)",
        "url": "https://books.google.com/books?id=OKcsAQAAMAAJ"
      }
    ],
    "@type": "Article",
    "headline": "Focos seismicos del Archipielago Filipino (1900): the Manila Observatory's seismic zonation of the Philippines"
  }
}