Tokuji Utsu

44 – Relationships between Magnitude Scales

This chapter describes relationships between magnitude scales. Magnitude scales were introduced by Richter and were designed for earthquakes in southern California recorded by the network of Wood-Anderson seismometers. This scale was then extended in many ways to apply to the data produced in various observational environments. New magnitude scales constructed, provide equal magnitude values to the same earthquakes or the earthquakes, which radiated the equal amount of energy. The chapter essentially considers earthquakes of all depths. The empirically obtained curves for the relationship between two magnitude scales represent earthquakes with average source characteristics. Significant deviation of a data point from the curve can usually be attributed to anomalous source characteristics of the event such as a nuclear explosion or a tsunami earthquake. Various magnitude scales considered include—namely, (1) local magnitude , (2) surface-wave magnitude, (3) body-wave magnitude, (4) moment magnitude, and (5) Kawasumis magnitude.

43 – Statistical Features of Seismicity

Seismicity studies are mostly statistical, because they deal with earthquake generation in groups. This chapter provides an overview of the studies related to statistical features of seismicity. The level of seismicity and its statistical properties may be affected by environmental conditions, such as stress, temperature, pore fluid pressure, mechanical and rheological properties of rocks, and large-scale tectonic regimes. The chapter also explores the physical mechanisms that cause the observed regularities in seismicity. To obtain reliable results from statistical analysis, a sufficient amount of high-quality data is also necessary. In most statistical studies, earthquakes are represented by point events in a five-dimensional space-time-size continuum. The five coordinates include longitude and latitude of epicenter, focal depth, origin time, and magnitude. Other quantities, which characterize an earthquake include fault-plane parameters, stress drop, fault rupture length, and rupture velocity. The results of a statistical analysis must be tested for significance. Every method for a significance test is based on certain assumptions.

42 – A List of Deadly Earthquakes in the World: 1500–2000

This chapter provides a list of some of the deadly earthquakes in the world from the span of 1500 through 2000 in which 50 or more people were killed. The data considered have been collected from various catalogs, research articles, and reports on global and regional earthquakes.