LgwaveQtomography in Central America

Abstract

Summary The lateral variation of Lg wave spectral attenuation in Central America was studied through tomographic inversion at various frequencies between 0.5 and 5 Hz, separately for each frequency. The input data set consisted of 558 travel paths recorded on short‐period and broad‐band seismic stations in the region. The size and quality of the data set were sufficient to resolve significant lateral variation in the Lg wave quality factor QLg. The average dependence of QLg with frequency was found to be QLg(f) = 182f0.84, corresponding to high attenuation. Low QLg values in the Nicaraguan Depression presented the most significant variation from the average. The strong attenuation of Lg waves in the Nicaraguan depression was also observed in the visual analysis of the seismograms. This observation is possibly explained by the near‐surface low‐velocity layers in the depression. Low QLg values were also found along the chain of volcanos due to increased scattering and partial melting beneath the volcanic belt. This study is the first attempt to determine QLg for Central America and to provide knowledge on attenuation of Lg waves needed for the prediction of ground motion during future earthquakes.

Lgwave attenuation in Britain

“… Q Lg was derived from the decay of spectral displacement amplitudes with distance for a range of individual frequencies following the method described by Ottemöller et al (2002). This approach has been successfully applied in southern Mexico (Ottemöller et al 2002), Central America (Ottemöller 2002) and Colombia (Ojeda & Ottemöller 2002). Regional average Q Lg was determined for 22 frequencies between 0.9 and 10.0 Hz.…”

Automatic computation of moment magnitudes for small earthquakes and the scaling of local to moment magnitude

“…In this case, therefore the attenuation parameter, t* ij , obtained from inversion will describe the average attenuation over all the travel paths (e.g. Q LG ; Ottemöller 2002). S ij ( r, r 0, … , n − 1 , λ 1, … , n ) is the amplitude decay with distance or ‘apparent geometrical spreading’, given by where r is the hypocentral distance, r n > 0 are distances at which the rate of decay changes from the λ n to the λ n +1 decay value, and r 0 is the rupture radius, which can be normalized to r 0 = 1 km without affecting M W (SP) as long as r 0 = 1 km is maintained in .…”

“…In this case, therefore the attenuation parameter, t * ij , obtained from inversion will describe the average attenuation over all the travel paths (e.g. Q LG ; Ottemöller 2002). S ij (r, r 0, ... ,n−1 , λ 1, ... ,n ) is the amplitude decay with distance or 'apparent geometrical spreading', given by…”

Frequency-dependent Lg-wave attenuation in northern Morocco

“…The method applied, together with the distance range and frequencies used are also indicated. Table 2 shows that tectonically active regions are related to low Lg Q values (e.g., Ford et al, 2008;Ottemöller, 2002;Ottemöller et al, 2002;Ojeda and Ottemöller, 2002;Ferdinand, 1998;Benz et al, 1997;Paul et al, 1996;Akinci et al, 1995;Chavez and Priestley, 1986) whereas more stable tectonic areas are associated with high Lg Q (e.g., Mousavi et al, 2014;McNamara et al, 2014;Singh et al, 2004;Chung and Lee, 2003;Shi et al, 1996;Chun et al, 1987;Hasegawa, 1985). Intermediate values of Lg Q and frequency-dependent exponent η correlate well with areas of moderate seismicity such as Xinjiang and adjacent regions The inverse methods used in this work utilize many source-receiver paths and solve for an average regional Lg Q estimate.…”