scholarly journals Characterizing large earthquakes before rupture is complete

2019 ◽  
Vol 5 (5) ◽  
pp. eaav2032 ◽  
Author(s):  
Diego Melgar ◽  
Gavin P. Hayes
Keyword(s):  
Seismic Energy ◽  
Rupture Process ◽  
Frequency Content ◽  
Ground Displacement ◽  
Initiation Phase ◽  
Radiated Seismic Energy ◽  
Slip Pulse ◽  
Rupture Duration ◽  
Large Earthquakes ◽  
Kinematic Properties

Whether earthquakes of different sizes are distinguishable early in their rupture process is a subject of debate. Studies have shown that the frequency content of radiated seismic energy in the first seconds of earthquakes scales with magnitude, implying determinism. Other studies have shown that recordings of ground displacement from small to moderate-sized earthquakes are indistinguishable, implying a universal early rupture process. Regardless of how earthquakes start, events of different sizes must be distinguishable at some point. If that difference occurs before the rupture duration of the smaller event, this implies some level of determinism. We show through analysis of a database of source time functions and near-source displacement records that, after an initiation phase, ruptures of M7 to M9 earthquakes organize into a slip pulse, the kinematic properties of which scale with magnitude. Hence, early in the rupture process—after about 10 s—large and very large earthquakes can be distinguished.

The rupture process of the Peru intermediate and deep earthquakes

2020 ◽  
Author(s):  
Carolina López Sánchez ◽  
Elisa Buforn ◽  
Maurizio Mattesini ◽  
Hernando Tavera
Keyword(s):  
Surface Effect ◽  
Seismic Energy ◽  
Rupture Process ◽  
Body Waves ◽  
P Wave ◽  
Nazca Plate ◽  
Radiated Seismic Energy ◽  
Anelastic Attenuation ◽  
Deep Earthquakes ◽  
Deep Depth

<p>The seismicity of Peru is associated with the subduction process of the Nazca plate under South America and characterized by the occurrence of shallow, intermediate and deep earthquakes. In this study, we focus our attention on the rupture process of earthquakes (Mw>6.0 ) that occurred during the period 2018-2019 at intermediate depth (50<h<200 km) and deep depth (500<h<700 km). Focal mechanisms have been estimated from slip inversion of body waves at teleseismic distances (Kikuchi and Kanamori, 1991). We investigate possible differences in the moment rate functions at different focal depths using our results and those provided by SCARDEC database. Furthermore, an estimation of the radiated seismic energy (E<sub>R</sub>) was provided from the direct integration of the velocity P wave recorded at teleseismic and regional distances, getting values between 10<sup>15 </sup>to 10<sup>16</sup> J. The data were corrected by geometrical spreading, anelastic attenuation, and free surface effect. These results are interpreted in terms of the seismotectonics of the region</p>

scholarly journals The Influence of Surface Topography on the Weak Ground Shaking in Kathmandu Valley during the 2015 Gorkha Earthquake, Nepal

Sensors ◽  
2020 ◽  
Vol 20 (3) ◽  
pp. 678
Author(s):  
Mark van der Meijde ◽  
Md Ashrafuzzaman ◽  
Norman Kerle ◽  
Saad Khan ◽  
Harald van der Werff
Keyword(s):  
Numerical Simulations ◽  
Surface Topography ◽  
Seismic Energy ◽  
Spectral Element ◽  
Kathmandu Valley ◽  
Ground Displacement ◽  
Gorkha Earthquake ◽  
Ground Shaking ◽  
Earthquake Scenarios ◽  
2015 Gorkha Earthquake

It remains elusive why there was only weak and limited ground shaking in Kathmandu valley during the 25 April 2015 Mw 7.8 Gorkha, Nepal, earthquake. Our spectral element numerical simulations show that, during this earthquake, surface topography restricted the propagation of seismic energy into the valley. The mountains diverted the incoming seismic wave mostly to the eastern and western margins of the valley. As a result, we find de-amplification of peak ground displacement in most of the valley interior. Modeling of alternative earthquake scenarios of the same magnitude occurring at different locations shows that these will affect the Kathmandu valley much more strongly, up to 2–3 times more, than the 2015 Gorkha earthquake did. This indicates that surface topography contributed to the reduced seismic shaking for this specific earthquake and lessened the earthquake impact within the valley.

Radiated seismic energy of earthquakes in the south–central region of the Gulf of California, Mexico

2018 ◽  
Vol 214 (2) ◽  
pp. 990-1003
Author(s):  
Raúl R Castro ◽  
Antonio Mendoza-Camberos ◽  
Arturo Pérez-Vertti
Keyword(s):  
Central Region ◽  
Gulf Of California ◽  
Seismic Energy ◽  
The South ◽  
Radiated Seismic Energy ◽  
South Central

Modeling Earthquakes Using Fractal Circular Patch Models with Lessons from the 2011 Tohoku-Oki Earthquake

2014 ◽  
Vol 9 (3) ◽  
pp. 264-271 ◽  
Author(s):  
Satoshi Ide ◽  
◽  
Hideo Aochi ◽  
Keyword(s):  
Fault Plane ◽  
Large Earthquake ◽  
Rupture Process ◽  
Fault System ◽  
External Loading ◽  
Dynamic Rupture ◽  
Consistent Model ◽  
Wide Scale ◽  
Seismicity Catalog ◽  
Large Earthquakes

Earthquakes occur in a complex hierarchical fault system, meaning that a realistic mechanically-consistent model is required to describe heterogeneity simply and over a wide scale. We developed a simple conceptual mechanical model using fractal circular patches associated with fracture energy on a fault plane. This model explains the complexity and scaling relation in the dynamic rupture process. We also show that such a fractal patch model is useful in simulating longterm seismicity in a hierarchal fault system by using external loading. In these studies, an earthquake of any magnitude appears as a completely random cascade growing from a small patch to larger patches. This model is thus potentially useful as a benchmarking scenario for evaluating probabilistic gain in probabilistic earthquake forecasts. The model is applied to the real case of the 2011 Tohoku-Oki earthquake based on prior information from a seismicity catalog to reproduce the complex rupture process of this very large earthquake and its resulting ground motion. Provided that a high-quality seismicity catalog is available for other regions, similar approach using this conceptual model may provide scenarios for other potential large earthquakes.

scholarly journals Continuous monitoring of seismic energy release associated with the 1994 Northridge earthquake and the 1992 Landers earthquake

1996 ◽  
Vol 86 (1A) ◽  
pp. 255-258 ◽  
Author(s):  
Sharon Kedar ◽  
Hiroo Kanamori
Keyword(s):  
Frequency Band ◽  
Southern California ◽  
Seismic Energy ◽  
Northridge Earthquake ◽  
Time Frequency ◽  
Landers Earthquake ◽  
Long Period ◽  
1992 Landers Earthquake ◽  
Large Earthquakes ◽  
1994 Northridge Earthquake

Abstract We have developed a method to detect long-period precursors for large earthquakes observed in southern California, if they occur. The method allows us to continuously monitor seismic energy radiation over a wide frequency band to investigate slow deformation in the crust (e.g., slow earthquakes), especially before large earthquakes. We used the long-period records (1 sample/sec) from TERRAscope, a broadband seismic network in southern California. The method consists of dividing the record into a series of overlapping 30-min-long windows, computing the spectra over a frequency band of 0.00055 to 0.1 Hz, and plotting them in the form of a time-frequency diagram called spectrogram. This procedure is repeated daily over a day-long record. We have analyzed the 17 January 1994 Northridge earthquake (Mw = 6.7), and the 28 June 1992 Landers earthquake (Mw = 7.3). No slow precursor with spectral amplitude measured over a duration of 30 min larger than that of a magnitude 3.7 was detected prior to either event. In other words, there was no precursor whose moment was larger than ∼0.003% of the mainshock.

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