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Seismogenic structure of the 26 March 2025 Yongqing ML4.6 earthquake and its implication for seismic hazard assessment
Estructura sismogénica del terremoto ML4.6 de Yongqing del 26 de marzo de 2025 y su implicación para la evaluación del peligro sísmico
DOI:
https://doi.org/10.15446/esrj.v30n(2).127009Keywords:
Yongqing earthquake, Seismogenic structure, Focal mechanism, Earthquake relocation, Rupture directivity, North China Plain, deep aquifers, Xiadian fault zone (en)terremoto de Yongqing, estructura sismogénica, mecanismo focal, relocalización de terremotos, directividad de ruptura, Llanura del Norte de China, evaluación del peligro sísmico, zona de falla Xiadian (es)
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Despite being an economically developed sedimentary basin with significant oil and gas production, the North China Plain exhibits anomalously high intraplate seismicity for a densely populated region. On 26 March 2025, a ML4.6 earthquake struck Yongqing County, following a similar ML4.8 event in 2018. Both earthquakes occurred near the epicentral region of the devastating 1679 M8 Sanhe-Pinggu earthquake and the seismically active Tianjin Gap, thus drew widespread public attention due to their tectonic implications. This paper conducted a comprehensive investigation of the 2025 Yongqing earthquake's seismogenic structure through the following points. (1) the first one is focal mechanisms inversion for the mainshock and three ML≥2.5 aftershocks, (2) the second one is the earthquake relocation by waveform cross-correlation, and (3) the third one is rupture direction estimation by centroid relative relocation and the spectral ratio technique. The results reveal that the 2025 ML4.6 earthquake ruptured a NE-striking, steeply dipping right-lateral strike-slip fault, with predominant SW-to-NE rupture propagation. This kinematic behavior shows striking similarity to the 2018 ML4.8 event, suggesting potential structural linkage. While both seismogenic faults remain unmapped in regional geological surveys, they potentially link with the Xiadian fault zone at mid-crustal levels. Nevertheless, our analysis reveals no conclusive evidence of structural continuity between these faults and the 1679 Sanhe-Pinggu earthquake rupture zone. The nearby Late Pleistocene-active Hexiwu Fault, which has historically produced only one M~5.5 earthquake recorded but exhibits persistent moderate seismicity, may be capable of generating larger ruptures in the future, highlighting the necessity for intensified seismic monitoring within this area.
A pesar de ser una cuenca sedimentaria económicamente desarrollada con una importante producción de petróleo y gas, la Llanura del Norte de China presenta una sismicidad intraplaca anómalamente alta para una región densamente poblada. El 26 de marzo de 2025, un terremoto de magnitud ML4.6 sacudió el condado de Yongqing, tras un evento similar de ML4.8 en 2018. Ambos terremotos ocurrieron cerca de la región epicentral del devastador terremoto de M8 Sanhe-Pinggu de 1679 y de la activa brecha sísmica de Tianjin, lo que atrajo una gran atención pública por sus implicaciones tectónicas. Este artículo realizó una investigación exhaustiva de la estructura sismogénica del terremoto de Yongqing de 2025 a través de los siguientes puntos: (1) inversión de los mecanismos focales para el sismo principal y tres réplicas de ML≥2.5, (2) relocalización del terremoto mediante correlación cruzada de formas de onda y (3) estimación de la dirección de ruptura mediante relocalización relativa del centroid y la técnica de relación espectral. Los resultados revelan que el terremoto ML4.6 de 2025 rompió una falla de deslizamiento lateral derecho con rumbo NE y buzamiento pronunciado, con una propagación de ruptura predominante de SW a NE. Este comportamiento cinemático muestra una notable similitud con el evento ML4.8 de 2018, lo que sugiere una posible conexión estructural. Aunque ambas fallas sismogénicas no están cartografiadas en los estudios geológicos regionales, podrían estar vinculadas con la zona de falla Xiadian a niveles medios de la corteza. Sin embargo, nuestro análisis no revela evidencia concluyente de continuidad estructural entre estas fallas y la zona de ruptura del terremoto Sanhe-Pinggu de 1679. La cercana Falla Hexiwu, activa durante el Pleistoceno tardío, que históricamente solo ha producido un terremoto registrado de M~5.5 pero muestra una sismicidad moderada persistente, podría ser capaz de generar rupturas mayores en el futuro, lo que resalta la necesidad de intensificar la monitorización sísmica en esta área.
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