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Earthquake Signal Imagery Classification

Introduction

Earthquake detection plays a critical role in disaster mitigation by providing early warnings that can help save lives. Classifying seismic signals efficiently can distinguish between actual earthquakes and background noise, enabling faster and more reliable earthquake early warning systems (EEWS). The rapid classification of earthquake signals is essential for alerting systems to issue warnings within seconds of a seismic event. Recent advancements in machine learning, particularly Convolutional Neural Networks (CNNs), have shown significant potential in the classification of earthquake signal imagery. These methods analyze seismograph recordings and distinguish between earthquake events and noise by classifying images generated from the signals.

Background

Earthquakes generate seismic waves that propagate through the Earth, and these waves are recorded by seismographs. The seismograph outputs can be converted into spectrograms—visual representations of the signal’s frequency content over time. These spectrograms can then be classified using CNN models, which have proven effective in image-based tasks across many domains. The key challenge is to develop efficient models that can rapidly classify these signals while maintaining high accuracy. This is especially important for real-time applications like EEWS.

Signal Processing Techniques for Earthquake Classification:

Seismic signals are typically divided into two types of waves: P-waves and S-waves. P-waves (primary waves) are compressional and the fastest seismic waves, while S-waves (secondary waves) are slower but more destructive. Most early warning systems focus on detecting P-waves to issue alerts before the more damaging S-waves arrive.

Seismograph signals often contain noise, which can interfere with accurate classification. To improve the accuracy of earthquake detection, signal processing techniques such as Fast Fourier Transform (FFT) and Wavelet Transform are applied to extract the relevant features from the seismic data. These processed signals are used to train machine learning models, particularly CNNs, to differentiate between earthquake events and noise.

Convolutional Neural Networks (CNN) for Earthquake Classification:

CNNs have emerged as a powerful tool for classifying seismic data. In CNN-based classification, earthquake signals are transformed into spectrograms, which serve as the input for the network. A typical CNN consists of convolutional layers that apply filters to the input images to detect features, followed by pooling layers that reduce the spatial dimensions of the data, and fully connected layers that perform the classification.

The advantage of using CNNs lies in their ability to automatically learn hierarchical feature representations from the data. In earthquake signal classification, CNNs can learn the key features that distinguish seismic events from noise by training on large labeled datasets, such as the Stanford Earthquake Dataset (STEAD).

Pruning Techniques to Optimize CNNs:

While large CNN models often provide high accuracy, they come with the disadvantage of high computational cost and longer inference times, which are not ideal for real-time applications like EEWS. To address this, pruning techniques have been developed to reduce the size of CNN models without significantly sacrificing accuracy.

Pruning removes redundant neurons and filters that have little impact on the model's performance. A common approach is to apply L2-norm pruning, which ranks the filters or neurons by their importance based on the L2-norm of their weights. Filters with low L2-norm values are considered less important and are pruned. After pruning, the model is retrained to fine-tune the remaining weights. This approach allows for faster inference times and reduced memory usage, making it more suitable for real-time earthquake detection.

Applications in Real-Time Earthquake Detection:

The CNN pruning method is particularly valuable for real-time earthquake detection systems, where computational efficiency is critical. By reducing the size of the CNN model, inference times can be significantly improved while maintaining high accuracy. For instance, by pruning 90% of the filters and neurons from a ResNet50-based CNN model, the inference time was reduced from 22.45 milliseconds to 3.6 milliseconds per image, with an accuracy of 99.405%. This makes it feasible to deploy the model in real-time detection systems that require quick responses.

Future Directions:

The integration of CNN-based earthquake detection systems with Internet of Things (IoT) devices and edge computing platforms is an emerging area of research. By deploying lightweight, pruned CNN models on edge devices, earthquake detection systems can become more scalable and responsive. Additionally, combining CNNs with other machine learning techniques, such as Recurrent Neural Networks (RNNs), may further improve the accuracy and generalization of these models across different seismic regions.

Conclusion

The use of CNNs for earthquake signal imagery classification provides a powerful tool for improving the accuracy and speed of earthquake early warning systems. Pruning techniques enable the deployment of these models in real-time systems by reducing their computational requirements without compromising accuracy. As earthquake detection technology continues to evolve, CNN-based models are expected to play a central role in mitigating the impact of earthquakes on society.

References

1. Ugwiri, M. A., Carratu, M., Espírito-Santo, A., Monte, G., & Paciello, V. (2020). Edge Sensor Signal Processing Algorithms for Earthquake Early Detection. IEEE Instrumentation and Measurement Society.

2. Atmaja, B. K., Adi, H. N., Mustika, I. W., Musaddid, A. T., & Hidayat, R. (2022). Development of CNN Pruning Method for Earthquake Signal Imagery Classification. 2022 14th International Conference on Information Technology and Electrical Engineering (ICITEE).

3. Mousavi, S. M., Sheng, Y., Zhu, W., & Beroza, G. C. (2019). STanford EArthquake Dataset (STEAD): A Global Data Set of Seismic Signals for AI. IEEE Access, 7, 179464-179476.