Method and device for detecting earthquakes
A method of detecting an earthquake is described, comprising receiving a signal representative of measurements of three-dimensional acceleration of the device as a function of time; frequency filtering of the signal; determining, from the filtered signal, data representative of acceleration directions as a function of time; an earthquake being detected if a) the magnitude of the acceleration is greater than a first threshold and the directions of the acceleration are substantially collinear with one another for a first time interval; or b) the directions of acceleration are substantially collinear with one another during a second time interval, and the directions of acceleration are substantially collinear with one another during a third time interval subsequent to the second time interval, and the directions of acceleration of the second interval and the third interval are substantially orthogonal.
1 . An earthquake detection method implemented by a device including at least one processor and a memory including software code, the at least one processor causing the device to implement the method when it executes the software code, the method comprising:
receiving a signal representative of measurements of a three-dimensional acceleration of the device as a function of time, the signal being received from an accelerometer sensor;
frequency filtering of the signal, the filtering being configured with a low cut-off frequency and a high cut-off frequency to exclude at least frequencies not corresponding to seismic wave frequencies;
determining, from the filtered signal, data representative of acceleration directions as a function of time;
an earthquake being detected if
a) the magnitude of the acceleration is greater than a first threshold and the directions of the acceleration are substantially collinear with one another for a first time interval; or
b) the directions of acceleration are substantially collinear with one another during a second time interval and the directions of acceleration are substantially collinear with one another during a third time interval subsequent to the second time interval, and the directions of acceleration of the second interval and the third interval are substantially orthogonal.
2 . The method according to claim 1 , wherein the cutoff frequencies are adapted to exclude frequencies corresponding to noise from the device environment.
3 . The method according to claim 1 , wherein determining data representative of directions of acceleration as a function of time is performed only if a magnitude of acceleration exceeds a second threshold before signal filtering and exceeds a third threshold after signal filtering.
4 . The method according to claim 3 , wherein the second and third thresholds are adapted to be above acceleration magnitudes corresponding to noise from the device environment.
5 . The method according to claim 3 , comprising adapting the cut-off frequencies, respectively adapting the second threshold and the third threshold, as a function of labeled historical acceleration data at a device operating location.
6 . The method according to claim 1 , wherein a determination of the collinearity of acceleration directions is carried out, comprising:
determining a hyperplane with respect to N consecutive measurement points from the signal and determining a direction normal to this plane, with N>1;
iterating the previous step on M sets of N points of a given time interval, with M>1;
concluding that there substantially is collinearity over the time interval under consideration if the angles of the N normal directions taken in pairs are within two ranges comprising 0° and 180°, respectively.
7 . The method according to claim 1 , wherein a determination of the orthogonality of acceleration directions is carried out, comprising:
determining a hyperplane with respect to N consecutive measurement points from the signal and determining a direction normal to this plane, with N>1;
iterating the previous step on two sets of N points in a given time interval;
concluding that there substantially is orthogonality if the angle between the normal directions of the two hyperplanes determined in the previous step are within two ranges comprising 90° and 270°, respectively.
8 . The method according to claim 1 , comprising, in response to the detection of an earthquake, generating a control signal for equipment securing a resource metered by the device.
9 . The method according to claim 1 , comprising, in response to the detection of an earthquake, generating an alert message to a server.
10 . The method according to claim 1 , wherein an earthquake is detected in case b) only if the magnitude of the acceleration exceeds a fourth threshold, lower than the first threshold.
11 . An earthquake detection device comprising a memory including software code and the processor, the processor being adapted, when executing the code, to cause the device to implement the method according claim 1 .
12 . The device according to claim 11 , comprising the three-dimensional accelerometer.
13 . A non-transitory computer-readable storage medium comprising instructions which, when executed by at least one processor, cause said at least one processor to execute the method of claim 1 .