GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 Calibraton of the local magnitude scale ( M L ) for eastern Cuba E. Diez 1 , D. Sandron 2 , M. Cute 1 , M. Guidarelli 2 1 Centro Nacional de Investgaciones Sismológicas (CENAIS), Santago de Cuba, Cuba. 2 Isttuto Nazionale di Oceanografa e di Geofsica Sperimentale — OGS, Sgonico, Italy. The frst atempt to create an internatonal standard for quantfying earthquake energy was made by Richter (1935), who introduced the local magnitude (M L ) as the logarithm of the maximum amplitude from zero to the maximum peak measured with a Wood-Anderson (WA) instrument (with 2800 amplifcaton and a natural period of 0.8 s [Anderson and Wood, 1925]), as follows: M L = log 10 A(R) − log 10 A 0 (R) where A(R) is the zero-to-peak amplitude in mm in a WA seismogram; R is the epicentral distance in km, and A 0 (R) is the distance correcton. The “calibraton point” was determined by setng M L =0 for a displacement amplitude of 1 thousandth of a millimeter at 100 km of epicentral distance. Recently, one hundredth of a millimeter at 17 km was chosen as an alternatve anchor point (Huton and Boore, 1987) and Uhrhammer and Collins (1990) corrected the statc gain value for the WA instrument to 2080 (confrmed by Sandron et al. (2015) using data from an original WA instrument stll in operaton). In 2013, the Internatonal Associaton of Seismology and Physics of the Earth’s Interior Magnitude Working Group (IASPEI, 2013) proposed the following general equaton: M L = log 10 (A)−nlog 10 (R)−KR−C−S in where A is the maximum amplitude in nanometers recorded by a simulated instrument such as WA with a statc gain of 1; R is the hypocentral distance in kilometers; C is a constant; and S is the correcton per staton due to local conditons (Bormann and Dewey, 2012). The parameters n and K represent the geometric dispersion and the anelastc atenuaton, respectvely (Bakun and Joyner, 1984). Several studies have been carried out to calibrate the M L equaton coefcients for diferent geographical areas around the world. In Cuba, in partcular, diferent approaches have been used to determine local earthquake magnitudes since the establishment of seismological statons in 1964. Álvarez and Bune (1977) and Álvarez et al. (1999, 2000) estmated the parameters for magnitude calculaton based on the results obtained from the evaluaton of energy class K or K- class, a measure of earthquake strength or magnitude of local and regional earthquakes used in the countries of the former Soviet Union, Cuba and Mongolia. The frst equaton of M L ,