The Japan Meteorological Agency (JMA) announced that an earthquake occurred in northeastern Chiba Prefecture at 00:07 on October 29, 2026 ^[1]. The agency detected the quake at the same time it occurred, 00:07 on October 29 ^[1]. The preliminary magnitude was given as 5.5, an update from the initial rapid estimate of 5.4 ^[1]. The focal depth was reported as 52 kilometers, revised from an initial estimate of about 50 kilometers ^[1]. According to the JMA, the earthquake's mechanism was a reverse-fault type with a pressure axis running west-northwest to east-southeast, occurring at the boundary between the Pacific Plate and the Philippine Sea Plate ^[1]. The maximum seismic intensity recorded was 5 lower (震度5弱), observed in the town of Yokoshibahikari in Chiba Prefecture, while intensities ranging from 4 to 1 were observed across a wide area from the Tohoku region to the Izu Islands ^[1]. As of 01:40 on October 29, the JMA reported that no subsequent earthquakes of seismic intensity 1 or greater had occurred following the main quake ^[1]. The agency also noted that long-period ground motion of class 1 was observed in northeastern Chiba Prefecture ^[1]. The JMA stated there is no tsunami concern from this earthquake ^[1]. The agency noted that in areas where shaking was strong, conditions may make rockfalls or landslides more likely to occur ^[1]. The JMA pointed to past cases in which earthquakes of similar scale followed a major quake at a rate of 10 to 20 percent, and said that in areas with strong shaking, the public should remain mindful of the possibility of earthquakes reaching a maximum seismic intensity of around 5 lower for roughly one week, with larger earthquakes most common in the following two to three days ^[1]. Full details, including charts and diagrams, are available in the JMA's full press release ^[1].

Source credit 出典：「令和８年10月29日00時07分頃の千葉県北東部の地震について」（気象庁）（https://www.jma.go.jp/jma/press/2610/29a/202610290210.html）、PDL1.0（https://www.digital.go.jp/resources/open_data/public_data_license_v1.0）を加工してJapan News (j.apan.news)が作成 This article is Japan News's own English summary of the Japanese original. It has been translated and edited by Japan News; it is not an official translation, and the Japan Meteorological Agency did not write or review it.