Investigation of the Ionosphere TEC Anomalies for Earthquake Precursor
detection using Machine Learning Models
Abstract
Real-time forecasting of anomalies in the Ionosphere TEC is attempted
using machine learning models such as Autoregressive Integrated Moving
Average (ARIMA) and Long Short-Term Memory (LSTM). The Performances of
both models were demonstrated on three Earthquakes (EQs), i.e. Mw 6.8,
2020 Indonesia, Mw 8.0, 2019 Peru and Mw 7.8, 2015 Nepal EQs. In this
study, GNSS-derived TEC values from the CODE server have been utilized
and the statistical boundary limits have been defined with 95%
confidence level for anomaly detection in daily TEC variations. The
training and test TEC dataset was divided into 8:2 ratio. After the data
processing the hyper model parameters were optimized for the training
dataset following which the TEC anomalies were validated by comparing
the forecasted and actual TEC values on the test dataset. For ARIMA
analysis, we start with the ADF test to check for stationarity of TEC
data and after observing the test-statistics critical values and p-value
we reject the null hypothesis. On calculating the ACF and PACF plots we
select model parameters values in accordance with the lowest AIC value.
While, for the LSTM model, we start with standardizing the training data
to have zero mean and unit variance. The model is fit using the ‘Adam’
version of stochastic gradient descent, optimized using the ‘mse’
loss-function and run through 250 epochs using the rectified linear
activation-function (ReLU) for better performance. Both the models were
successfully able to detect and predict significant evidence for
pre-seismic ionospheric TEC anomalies on 01 May 2020, 20 May 2019 and 11
April 2015 respectively before the occurrences of Indonesia, Peru and
Nepal EQs. The time series analysis of forecasted TEC data revealed that
the RMSE and MAPE error on the anomalous day was found to be
significantly higher than the preceding non-anomalous day error and the
overall forecasted error. Both ARIMA and LSTM models performed well for
Indonesia and Peru EQs, forecasting TEC anomalies accurately within the
5-6 day window before the EQ, but the LSTM model outshined the former in
long term TEC forecasting for the Nepal EQ performing well in the 11 day
window before the EQ. Overall, the LSTM model was found to be more
precise especially in long term forecasting and was also able to detect
the weaker TEC anomalies which went unnoticed in the ARIMA model.