Seismic Source Directivity from Doppler Effect Analysis, Part I: Theory

The directivity effects, a characteristic of finiteness seismic sources, are generated by the rupture in preferential directions. Those effects are manifested through different cadencies in the seismological measures from azimuthally distributed stations. The apparent durations are expressed as (e.g. Aki and Richards, 1980), (1), where L, v, c and ??are, respectively, the fault length, the rupture velocity, the wave velocity and the angle between rupture direction and ray. This time duration can be measured directly from waveform or indirectly from Relative Source Time Function (RSTF). Equation (1) is deduced from a simple source model (Haskell model) that considers unidirectional uniform rupture propagation and a homogeneous elastic isotropic media. If we consider a more general propagation model, with spherical concentric layers, we obtain (2), where p is the ray parameter and the earth radius. Similar equation can be obtained through physical considerations about a model composed by a sequence of subevents unilater- ally distributed along a line (Doppler Effect). Based on the same considerations we can do a more detailed analysis through (3), where is the time interval between 2 identified pulses in the rupture referential and j indicate the number of station. Based on this theory, we have developed a computational code DIRDOP (DIRectivity DOPpler effect) which determines the rupture direction and velocity from pulse durations observed in waveforms or RSTF. We used this code to analyse recent major seismic events including the unilateral 23 June, 1999 Arequipa (Peru, Mw=8.2) earthquake and the bilateral 21 May 2003 Boumerdes (Algeria, Mw=6.7) earthquake amongst others. The results are similar to those obtained by other methods

The 2007 Azores earthquakes: A case of triggering?

On 5 April (Mw=6.3) and 7 April 2007 (Mw=6.1 ) two earthquakes occur at the Formigas Islets (Azores Islands), both with same epicenter and felt (I=V/VI MSK) in S. Miguel Island. The rupture process of these earthquakes has been studied from body wave inversion of broad band data at telesesimic distances. Results obtained shown normal faulting for both shocks, with planes oriented in NW–SE direction, with focus at shallow depth (10 km and 6 km respectively). The slip distribution over the fault plane (152/44/-88) shows for the 05-04-07 event, the rupture propagating downward and a duration of 12s for the source time function. For the 07-04-07 event, the slip distribution over the fault plane (125/52/-81) shows de rupture propagating downward and duration of 10s for the STF. From these results we have estimated the static Coulomb stress change. We find that the static stress change caused by the 5 April event is higher, about 2 bar at epicenter the location of the second event (April 7), triggering the second rupture. Locations of aftershocks do not agree well with areas of increased Coulomb failure stress, which can be explained by the complexities of the rupture process oy by uncertainties at the hypocerter locatio

Perfil andrológico de touros nelore criados extensivamente no planalto e no Pantanal sul-mato-grossense.

bitstream/item/56426/1/CT100-lancado.pdfNa publicação: Juliana Corrêa Borges

Recent Seismic Activity in the Azores Region

This seismic activity in the Azores Region is characterized by sequences of low-magnitude events, usually with epicenter off-shore. These seismic sequences are sometimes triggered by larger events, felt by the population, that could produce significant material and human losses. This characteristic is confirmed by the historical and instrumental seismicity, in particular by the recent earthquakes occurred on 1980 (Mw=6.8), 1997 (Mw=6.2), 1998 (Mw=6.2) and 2007 (Mw=6.3, Mw=6.1). The mechanism responsible for this spatial and temporal seismic pattern still yet not very well known. In this work we discuss the recent (2007) seismic activity of the Azores region by analyzing the spatial and temporal distribution of seismic events associated with two sequences with different characteristics. The fisrt one is a seismic swarm started on April 21st 2007, centered at about 40 kilometers west of the Faial Island (maximum magnitude mb=4.0). The second one corresponds to an aftershock sequence associated to the events of 2007/04/05 (Mw=6.3) and 2007/04/07 (Mw=6.1), both with epicenter in the Formigas Islets and felt (I=V/VI in Mercali scale) in S. Miguel. We calculate the static Coulomb stress change for both events using focal mechanisms derived from the inversion of body waves. We find that the static stress change caused by the April 5 event is higher, about 2 bar at the location of the second event (April 7), triggering the second rupture. Locations of aftershocks do not agree well with areas of increased Coulomb failure stress

Optimized Multimode Interference Fiber Based Refractometer in A Reflective Interrogation Scheme

A fiber based refractometer in a reflective interrogation scheme is investigated and optimized. A thin gold film was deposited on the tip of a coreless fiber section, which is spliced with a single mode fiber. The coreless fiber is a multimode waveguide, and the observed effects are due to multimode interference. To investigate and optimize the structure, the multimode part of the sensor is built with 3 different lengths: 58 mm, 29 mm and 17 mm. We use a broadband light source ranging from 1475 nm to 1650 nm and we test the sensors with liquids of varying refractive indices, from 1.333 to 1.438. Our results show that for a fixed wavelength, the sensor sensitivity is independent of the multimode fiber length, but we observed a sensitivity increase of approximately 0.7 nm/RIU for a one-nanometer increase in wavelength

Still a New Problem for Defeasibility: A Rejoinder to Borges

I objected that the defeasibility theory of knowledge prohibits you from knowing that you know that p if your knowledge that p is a posteriori. Rodrigo Borges claims that Peter Klein has already satisfactorily answered a version of my objection. He attempts to defend Klein’s reply and argues that my objection fails because a principle on which it is based is false.I will show that my objection is not a version of the old one that Klein attempts (unsuccessfully) to address, that Borges’ defence of Klein’s reply fails and that his argument against my new objection leaves it untouched

Enhancing the Sensitivity of SMS Fiber Sensors by the Use of High Refractive Index Coatings

This paper presents a study on the behavior of single-mode/multimode/single-mode sensors with diamond-like carbon coating of high refractive index. Spectra and response for different values of the external medium refractive index are recorded and analyzed