<p>Magnitude determination in earthquake early warning (EEW) systems remains a significant challenge. On April 2, 2024, a Mw 7.4 earthquake struck Taiwan. The Central Weather Administration (CWA) EEW system estimated the magnitude at 6.8 within 15 s, resulting in no alerts for the Taipei metropolitan region, which experienced an intensity level of 5 lower (PGV ≥ 15 cm/s) on the CWA’s intensity scale. The lack of warning alerts sparked widespread complaints, highlighting concerns over the effectiveness of the current EEW system. This study compares the parameter cumulative absolute absement (<InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_97748_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="43" /> </InlineMediaObject> <EquationSource Format="TEX">\(\:CAA\)</EquationSource> </InlineEquation>) with the currently used parameters — the peak vertical displacement (<InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_97748_Article_IEq2.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="27" /> </InlineMediaObject> <EquationSource Format="TEX">\(\:Pd\)</EquationSource> </InlineEquation>) and the average period (<InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_97748_Article_IEq3.gif" Format="GIF" Height="12" Rendition="HTML" Resolution="72" Type="Linedraw" Width="21" /> </InlineMediaObject> <EquationSource Format="TEX">\(\:{\tau\:}_{c}\)</EquationSource> </InlineEquation>) — for quick magnitude estimation of the April 2, 2024, earthquake using low-cost sensors. Results indicate that <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_97748_Article_IEq4.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="27" /> </InlineMediaObject> <EquationSource Format="TEX">\(\:Pd\)</EquationSource> </InlineEquation> provides closer estimates of the CWA final M<sub>L</sub> but carries higher uncertainty. Conversely, <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_97748_Article_IEq5.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="43" /> </InlineMediaObject> <EquationSource Format="TEX">\(\:CAA\)</EquationSource> </InlineEquation> yields more stable estimates. Notably, the northward rupture of this earthquake caused overestimation when only northern stations were used and underestimation with only southern stations, underscoring the critical importance of proper station distribution. Interestingly, <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41598_2025_97748_Article_IEq6.gif" Format="GIF" Height="12" Rendition="HTML" Resolution="72" Type="Linedraw" Width="21" /> </InlineMediaObject> <EquationSource Format="TEX">\(\:{\tau\:}_{c}\)</EquationSource> </InlineEquation> demonstrates less sensitivity to rupture directionality, suggesting its potential robustness in such scenarios. These findings underscore optimizing parameter selection and station configuration for robust EEW, enabling rapid magnitude estimation to significantly reduce losses.</p>

Magnitude determination for earthquake early warning using P-alert low-cost sensors during 2024 Mw7.4 Hualien, Taiwan earthquake

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2025年4月12日

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Yueh-Ho Lin,
Yih-Min Wu

摘要

Magnitude determination in earthquake early warning (EEW) systems remains a significant challenge. On April 2, 2024, a Mw 7.4 earthquake struck Taiwan. The Central Weather Administration (CWA) EEW system estimated the magnitude at 6.8 within 15 s, resulting in no alerts for the Taipei metropolitan region, which experienced an intensity level of 5 lower (PGV ≥ 15 cm/s) on the CWA’s intensity scale. The lack of warning alerts sparked widespread complaints, highlighting concerns over the effectiveness of the current EEW system. This study compares the parameter cumulative absolute absement ( \(\:CAA\) ) with the currently used parameters — the peak vertical displacement ( \(\:Pd\) ) and the average period ( \(\:{\tau\:}_{c}\) ) — for quick magnitude estimation of the April 2, 2024, earthquake using low-cost sensors. Results indicate that \(\:Pd\) provides closer estimates of the CWA final M_L but carries higher uncertainty. Conversely, \(\:CAA\) yields more stable estimates. Notably, the northward rupture of this earthquake caused overestimation when only northern stations were used and underestimation with only southern stations, underscoring the critical importance of proper station distribution. Interestingly, \(\:{\tau\:}_{c}\) demonstrates less sensitivity to rupture directionality, suggesting its potential robustness in such scenarios. These findings underscore optimizing parameter selection and station configuration for robust EEW, enabling rapid magnitude estimation to significantly reduce losses.