A Method of Hypocentral Location by Means of an Earthquake’s First Motion

Abstract An automatic detection algorithm has been developed which is capable of time P-phase arrivals of both local and teleseismic earthquakes, but rejects noise bursts and transient events. For each signal trace, the envelope function is calculated and passed through a nonlinear amplifier. The resulting signal is then subjected to a statistical analysis to yield arrival time, first motion, and a measure of reliability to be placed on the P-arrival pick. An incorporated dynamic threshold lets the algorithm become very sensitive; thus, even weak signals are timed precisely. During an extended performance evaluation on a data set comprising 789 P phases of local events and 1857 P phases of teleseismic events picked by an analyst, the automatic picker selected 66 per cent of the local phases and 90 per cent of the teleseismic phases. The accuracy of the automatic picks was “ideal” (i.e., could not be improved by the analyst) for 60 per cent of the local events and 63 per cent of the teleseismic events.

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Efficient lock and home security system

Algerian Journal of Signals and Systems ◽

10.51485/ajss.v4i2.87 ◽

2019 ◽

Vol 4 (2) ◽

pp. 112-120

Author(s):

Hadjira BELAIDI ◽

Nour-El-Houda MEDDAH

Keyword(s):

Protected Area ◽

Smart Phone ◽

Security System ◽

Motion Sensors ◽

Entire System ◽

Security Systems ◽

Home Security ◽

Rfid Reader ◽

First Motion

This work deals with lock and home security systems. First, Motion sensors detect movement indoors and outdoors to guard against intruders, protect valuables and more. Thus, if any movement, RFID reader will be activated and database will be scanned to identify the persons who have the access to the home. This enhances the effectiveness of the security system and provides the user with the complete, whole-house protection he needs. An RFID badge can be used to unlock the door and access to the home. Alerts also are received on the smart phone if motion is sensed in a protected area inside or outside; giving the user the information it needs to act quickly. The door can also be remotely locked/unlocked. A microcontroller (ATmega2560) is used to control the entire system, and GSM is used to send alerts to the Smartphone. An Ethernet shield that connects the microcontroller to the database (DB) is also added.

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A simple P-wave polarization analysis: its application to earthquake location

Annals of Geophysics ◽

10.4401/ag-4181 ◽

1994 ◽

Vol 37 (5) ◽

Author(s):

B. Alessandrini ◽

M. Cattaneo ◽

M. Demartin ◽

M. Gasperini ◽

V. Lanza

Keyword(s):

Ground Motion ◽

Seismic Wave ◽

Heterogeneous Media ◽

Seismic Wave Propagation ◽

Least Square ◽

P Wave ◽

Motion Direction ◽

Arrival Times ◽

Hypocentral Location ◽

Ray Path

We present a method for hypocentral location which takes into account all three components of ground motion and not only the vertical one, as it is usually done by standard least-square techniques applied to arrival times. Assuming that P-wave particle motion direction corresponds to the propagation direction of the seismic wave, we carried out a simple statistical analysis of ground motion amplitudes, carefully using three-component records. We obtained the azimuth and the emersion angle of the seismic ray, which, added to Pg and Sg arrival times, allowed us to find reliable hypocentral coordinates of some local events by means of a ray-tracing technique. We compared our locations to those obtained using a least-square technique: our polarization method's dependence on the accuracy of the model used (on the contrary, the least-square technique proved to be quite stable with respect to changes in the model's velocity parameters) led us to conclude that polarization data provide coherent information on the true ray-path and can be successfully used for both location procedures and seismic wave propagation studizs in strongly heterogeneous media.

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Minimising the computational time of a waveform based location algorithm

10.5194/egusphere-egu21-15664 ◽

2021 ◽

Author(s):

Emmanouil Parastatidis ◽

Stella Pytharouli ◽

Lina Stankovic ◽

Vladimir Stankovic ◽

Peidong Shi

Keyword(s):

Computer Architecture ◽

Time Window ◽

Real Data ◽

Computational Time ◽

Enhanced Geothermal Systems ◽

Geothermal Systems ◽

Migration Method ◽

Location Algorithm ◽

Hypocentral Location ◽

Grid Interval

Accurate and fast localisation of microseismic events is a requirement for a number of applications, e.g. mining, enhanced geothermal systems. New methods for event localisation have been proposed over the last decades. The waveform-based methods are of the most recent developed ones and their main advantage is the ability to locate weak seismic events. Despite this, these methods are demanding in terms of computational time, making real-time seismic event localisation very difficult. In this work, we further develop a waveform-based method, the Multichannel coherency migration method (MCM), to improve the computational time. The computational time for the MCM algorithm has been reported to linearly depend on several parameters, such as the number of stations, the length of the waveform time window, the computer architecture, and the volume of the area we are searching for the hypocentre. To minimise the computational time we need to decrease one or more of the above parameters without compromising the accuracy of the result. We break the localisation procedure into several steps: (1) we locate the event with a relatively large spatial grid interval which will give less potential hypocentral locations and less calculations as a result. (2) Based on the results of step (1) and the locations of maximum coherencies we decrease the grid volume to a quarter of the original volume and the spatial interval to half the original, focusing only around the area identified in step (1). Step (2) is repeated several times for decreased grid volumes and spatial intervals until the hypocentral location does not significantly change any more. We tested this approach on both synthetic and real data. We find that while the accuracy of the hypocentre is not compromised, the computational time is up to &#160;125,000 times shorter. &#160;&#160;&#160;

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Implementation of a new real time seismicity detector for the Mayotte crisis

10.5194/egusphere-egu21-10646 ◽

2021 ◽

Author(s):

Jean-Marie Saurel ◽

Lise Retailleau ◽

Weiqiang Zhu ◽

Simon Issartel ◽

Claudio Satriano ◽

...

Keyword(s):

Real Time ◽

Volcanic Activity ◽

A Priori ◽

Processing System ◽

Activity Level ◽

Phase Identification ◽

Real Time Processing ◽

S Waves ◽

Hypocentral Location ◽

New Processing

Seismology is one of the main techniques used to monitor volcanic activity worldwide. Seismicity analysis through several seismic sensor deployments has been used to monitor Mayotte volcano crisis since its beginning in May 2018. Because volcanic activity can evolve rapidly, efficient and accurate seismicity detectors are crucial to assess in real-time the activity level of the volcano and, if needed, to issue timely warnings.&#160;Traditional real-time seismic processing software, such as EarthWorm or SeisComP, use phase onset pickers followed by a phase association algorithm to declare an event and proceed with its location. Real-time phase pickers usually cannot identify whether the detected phase is a P or S arrival and this decision or assumption is made by the associator. The lack of S arrival has an obvious impact on the hypocentral location quality. S-phases can also help detection on small earthquakes where weak P-phases can be missed.&#160;We implemented the deep neural network-based method PhaseNet to identify in real-time seismic P and S waves on 3-component seismometers deployed on Mayotte island. We also built an interface to subsequently process PhaseNet results and send pick objects to EarthWorm. We use EarthWorm binder_ew associator module specifically tuned for PhaseNet a priori phase identification to detect and locate the events, which are finally archived in a SeisComP database. We implemented this innovative real-time processing system for the REVOSIMA (Reseau de surveillance Volcanologique et Sismologique de Mayotte) hosted at OVPF (Observatoire Volcanologique du Piton de la Fournaise). We assess the robustness of the algorithm by comparing the results to existing automatic and manually detected seismicity catalogs.&#160;We show that the existing SeisComP automatic system is outperformed by our new algorithm, both in number of earthquake detections and location reliability. Our implementation also detects more events than the daily manual data screening. While this promising new processing system was first applied to study the Mayotte seismicity, it can be used in any seismic active zone, of volcanic or tectonic origin. Indeed, it will be installed at Martinique volcanic and seismic observatory later this year.

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