insights into the mysteries of materials and dynamics in the Earth's deep interior

Unprecedented insights into the mysteries of materials and dynamics in the Earth's deep interior. Professor K. Hirose, from the Department of Earth and Planetary Sciences of the Tokyo Institute of Technology, explains recent experiments using ultra high pressure and temperature for clarification of materials and their dynamics inside the Earth. Their results are very interesting and will contribute to the understanding of the dynamics and internal process of the material in the earth's interior.

Geodynamic and seismotectonic context of Peru

The subduction of the Nazca plate beneath South America constitutes the major tectonic characteristic in Peru. According to magnetic and geodetic data, the Nazca plate is continuously moving north-eastward (azimuth 78 degress )with an average velocity of 6 cm/yr (DeMets et al., 1990; Norabuena et al., 1999). This rapid convergence causes a high seismic coupling along the subduction interface giving raise to the occurrence of interplate and intraplate earthquakes with different magnitudes and depths. As a result of this process, different geomorphological structures and tectocni features have been created such as: the Peru-Chile trench, the Andean cordillera, the volcanic chain and fault systems. In case of the fault systems those are also sources of seismicity but of lower magnitudes. The figure shows all these features.

-  The Peru-Chile trench: is a structure emplaced parallel to the Peruvian coast with a distance of about 160 km from the coast, bordering the contact between the Nazca plate and the South America plate.

-  The Andean cordillera: the most obvious tectonic feature product of the continuous interaction of the Nazca plate, covers an area of 7,500 km, with heights of 6,000 m and higher. The volcanic chain is located in the southern part of Peru from 14º N to 25º S in Chile. Finally, fault systems are result of the deformation in the continental crust due to subduction process.

Different authors have proposed that the subduction zone could be divided into three zones according to its seismic activity (North, Central and South), this zones might be separated by two prominent geomorphologic features on the subduction plate: the Mendana fracture zone (10ºS) and the Nazca ridge (15ºS). The Nazca ridge location is considered as a barrier of rupture propagation as observed in the last Pisco earthquake (Mw8.0) in 2007 (Perfettini et al., 2010; Sladen et al., 2010). However, Okal et al. (2006), using tsunami simulations for the 1868 and 1687 events suggest that the Nazca ridge appears more like a hurdle than a barrier serving as a rupture barrier for certain events such as the 1604 event for the south and 1746 event to the north. Moreover, this feature is considered as a transition between a flat subduction zone to the north and a subduction steeply dipping to the south, with different azimuth of the shore line and seismicity activity (Okal et al., 2006; Sladen et al., 2010). The Mendana fracture zone is considered as a transition zone with a difference crustal age of about 10 Myr between north of the Mendana fracture zone and off the central and south of Peru (Muller et al., 1997).

- The volcanic chain: Located in the south of Peru from 14º S to 25º S in Chile. This chain is distributed along the Andean cordillera following an aparent linearity on NW-SE direction. Among the main volcanoes located in southern Peru: Coropuna (6425 m), Sabancaya (5795 m), Misti (5825 m), Ubinas (5672 m.), Chachani (3745 m.), Huaynaputina (4800 m.), Tutupaca (5806 m.), Yucamane (5508 m.). In northern and central Peru volcanic activity have disappeared approximately 8 Ma, due to changes in the form of the subduction process (Moroco 1980).

- The fault systems: are result of constant deformation process in the continental crust due to the subduction process. These faults are present in great number, from North to South along Sub-Andean zone and the eastern side of the Andes Mountains creating major folds in the contact with the Brazilian Shield. The main fault systems located in Peru are: Alto Mayo (AM), Satipo (SA), Madre de Dios (MD),  in less proportion located on the high Cordillera and the Altiplano: the Cordillera Blanca (CB), Huaytapallana (HU), Tambomachay (TM). All fault systems owe their origin to a heterogeneous distribution of tensional and compressional efforts within thecontinent (James, 1978).

VIDEO: El gran terremoto de Tohoku: premonitores, sismo principal y réplicas

Si bien el sismo de Tohoku ocurrido el 11 de marzo de 2011alcanzó una gran magnitud 9.1Mw, este sismo fue precedido por un precursor de magnitud 7.2Mw el día 9 de Marzo. La animación posteada por Nathan B. (investigador del Pacific Tsunami Warning Center) muestra en 4 minutos (equivalentes al periodo de enero a Septiembre) la distribución espacio-temporal de los eventos premonitores, evento principal y réplicas de este gran sismo. Al observar la actividad sismica durante estos nueve meses se aprecia que durante los primeros meses la actividad sismica de fondo es normal o típica de la región, luego al producirse el evento premonitor le suceden el sismo principal y la serie de replicas que terminan por completar y estabilizar el área de ruptura del sismo. De este contexto se puede desprender que el evento premonitor del 9 de Marzo corresponde a lo que los autores que estudian el ciclo sismico denominan etapa de carga o fase pre-sismica, luego el sismo principal del 11 de Marzo corresponde a la etapa en la que se libera la energia sismica usualmente denominada fase co-sismica y finalmente la serie de réplicas que al parecer a la fecha aún no cesan corresponde a la etapa de relajación denominada fase post-sismica.

En el video cada segundo corresponde aproximadamente a 1 día, y la magnitud de los sismos se presenta en escala logaritmica.

Debris avalanche simulation

This experiment has been done at IGP in Aug. 2011. The ingredients used were: Honey, fine sugar, sugar and little bit of patience... :-)

Welcome to geosoft

Very powerful!!!

earthquake classification according to its magnitude

Earthquakes are result of a sudden release of energy that creates seismic waves. Energy released from earthquakes includes (1) energy dissipated as heat through friction and (2) energy elastically radiated through the earth. Only the radiated energy can be measured since it propagates and shakes the earth surface.

Depending on their magnitude earthquakes are classified from minor to great:

CLASS          MAGNITUDE

 Great         -->    8 or more

 Major        -->    7 to 7.9

 Strong       -->    6 to 6.9

 Moderate  -->    5 to 5.9

 Light         -->    4 to 4.9

 Minor        -->    3 to 3.9

An approximated estimation of the number of earthquakes per year, its magnitude and effects:
Magnitude       Earthquake Effects         Estimated Number
2.5 or less           Usually not felt,                       900,000
2.5 to 5.4             Often felt, minor damage.        30,000
5.5 to 6.0             Slight damage to structures.        500
6.1 to 6.9             Damage in  populated areas.       100
7.0 to 7.9             Serious damage.                            20
8.0 or greater      Collapse of towns.             One every 5 to 10 years

1D VELOCITY MODEL FOR NORTHERN PERU USING LOCAL EARTHQUAKE DATA

We compute a new 1D velocity model for northern Peru by inverting the  arrival times of P and S waves. We follow the methodology based on the non-linear inversion using the Veslest algorithm. We use 1593 local earthquakes recorded during six years (1996-2001) by a local seismic network. The inversion was carried out using 2897 arrivals of P and S waves, corresponding to 547 earthquakes. We evaluated several models considering different velocities and thicknesses layer, this process allowed us to obtain 12 well-defined models that were re-evaluated through the earthquakes relocation. We selected a model that which showed reduction in the location and the root mean square (rms).
The 1D velocity model that we propose consists of six layers with velocities of Vp = 5.66 km/s for the first layer, to 7.92 km/s for the last one. This model defines the boundary between the crust and mantle (Mohorovicic) at a depth of 45 km below our study area. The earthquake relocation shows a better distribution of hypocenters in surface and depth and also shows a reduction of 35% in the rms values. This model constitutes a major contribution to the knowledge of the structure velocity in northern Peru and can be used as a reference in software for earthquake location, as well as in seismicity, tectonics and seismic risk studies in northern Peru.
Published in: Boletín de la Sociedad Geologica del Perú