A New Ground-Motion Prediction Equation of Japanese Instrumental Seismic Intensities Reflecting Source Type Characteristics in Japan

ABSTRACT A new equation for predicting Japanese instrumental seismic intensities at arbitrary surface sites in Japan for Mw 5.4–8.7 and distances ranging from 10 to 1000 km was derived from approximately 30,000 observed intensities for various types of earthquakes. The equation incorporates the differences in the subsurface characteristics immediately beneath each site using VS30. The equation can also predict the abnormal intensities (which are indispensable in Japan) due to subducting slabs using the depth of the slab surface beneath each site from the Crustal Activity Modeling Program standard plate model. The prediction equation can be applied to five source types: Pacific Ocean plate (PAC) interplate, PAC intraplate, very shallow crustal, shallow (≤50 km) Philippine Sea plate (PHS) intraplate, and intermediate-depth (>50 km) PHS intraplate earthquakes. Although the equation is applicable at various magnitudes and distances, the standard deviations (σ) are 0.5–0.6, which are smaller than those of other equations with narrower distance ranges. Smaller σ values were achieved by the inversion of 29,837 Japanese instrumental seismic intensities from 68 selected earthquakes of five source types with a common site effect at each station. A deep Mw 7.9 earthquake that occurred at a depth of 680 km in 2015 near the Ogasawara Islands and subjected all of Japan to long-duration shaking due to waves propagating through the mantle was effectively employed to constrain the VS30 term of the equation. The equations for PAC interplate and very shallow earthquakes were validated by seven earthquakes that were not used for the inversion; the standard deviations for these earthquakes fell in the range of 0.41–0.53. The formula for very shallow crustal earthquakes is also able to predict the intensities of PHS interplate earthquakes. Hence, this equation is useful not only for engineering applications but also for historical seismology to distinguish the source types of ancient earthquakes.

How Historical Seismology Can Benefit from Bureaucracy: The Case of the “Lettere Patenti” in the City of Rome in 1703

The 1703 Mw 6.9 seismic sequence (I0 11 Mercalli–Cancani–Sieberg scale) was one of the most important crises ever occurred in Italy and has left a deep mark on the seismic history of cities and towns of central Italy. Abundant documents testify the damage suffered by the city of Rome during this sequence; however, the descriptions are mainly referred to monumental buildings. For the recent macroseismic practice, such edifices are not statistically representative when used for assessing macroseismic intensity; instead, the information about residential housing provides reliable data especially when using the European Macroseismic Scale 1998. In this work, we show that useful information regarding the ordinary residential stock can be retrieved in the bureaucratic documentation, apparently distant from the repertoires traditionally used for historical seismology studies. In particular, we used administrative acts granted by the government of Rome to authorize maintenance works on the external parts of the buildings, namely the “Lettere Patenti.” The scrutiny of these sources allowed us to enrich the available dataset introducing 93 new damage points found on civil building stock spread in the historic center of Rome. The new dataset contributes to better define the picture of the effects of the 1703 seismic sequence in Rome, which allowed us to assess macroseismic intensity with more confidence.

The Global Earthquake History

The study of earthquakes from historical sources, or historical seismology, was considered an early priority for the Global Earthquake Model (GEM) project, which commissioned a study of historical seismicity on a global scale. This was the Global Earthquake History (GEH) project, led jointly by the Istituto Nazionale di Geofisica e Vulcanologia (INGV; Milan, Italy) and the British Geological Survey (BGS; UK). GEH was structured around three complementary deliverables: archive, catalog, and the Web infrastructure designed to store both the archive and catalog. The Global Historical Earthquake Archive (GHEA) provides a complete account of the global situation in historical seismology for large earthquakes. From GHEA, the Global Historical Earthquake Catalogue (GHEC v1.0) was derived—a world catalog of earthquakes for the period 1000–1903, with magnitudes of Mw7 and over. Though much remains to be done, the data here presented show that the compilation of both archive and catalog contribute to an improved understanding of the Global Earthquake History.

Catalogues of historical earthquakes in Italy

A complete survey of historical earthquake investigation in Italy cannot be compressed into a few pages, since it would entail making a summary of widely different phases of research (performed by past scholars and by contemporary scientists and historians) and taking into account the widely different historical contexts, methodological assumptions and critical awareness of each of them. This short note only purposes to chart the main stages of the progress made by Italian historical seismology, from the late 17th century compilation by Bonito(1691) up to the latest parametric catalogue (Working Group CPTI, 1999).