Origin Time of the 1854 Ansei–Tokai Tsunami Estimated from Tide Gauge Records on the West Coast of North America

Abstract

We estimated the origin time of the 1854 Ansei–Tokai tsunami from the tsunami waveforms recorded at three tide gauge stations (Astoria, San Francisco, and San Diego) on the west coast of North America. The tsunami signal is apparent in the San Francisco and San Diego records, and the arrival time was 0–1 p.m. Greenwich Mean Time (GMT) on 23 December 1854, whereas the tsunami signal of Astoria is ambiguous, and the arrival time could not be determined from the waveform. The simulated waveforms on the basis of nonlinear dispersive wave theory by assuming an origin time of 0 a.m. GMT on 23 December arrived earlier than the observations. Cross-correlation functions between the observed and simulated waveforms recorded at San Francisco and San Diego showed a time gap between them of approximately 30 min. Based on these results, we concluded that the origin time of the 1854 Ansei–Tokai tsunami was approximately 00:30 a.m. GMT or 09:46 local time on 23 December. Our result is roughly consistent with reports by a Russian frigate anchored in Shimoda Bay, ranging the earthquake between 09:00 and 09:45 and the tsunami between 09:30 and 10:00. The earthquake was also reported in historical Japanese documents ranging from 8 and 10 o’clock in local time.

Time Difference Between the 1854 CE Ansei–Tokai and Ansei–Nankai Earthquakes Estimated from Distant Tsunami Waveforms on the West Coast of North America

“…By comparing the observations with simulations in which it was assumed that the 1854 CE Ansei-Nankai tsunami originated at 07:00 GMT on 24 December, we found that the observed waveforms of the Ansei-Nankai tsunami lagged behind the simulated waveforms by 0.4 h. Therefore, we estimated the origin time of Ansei-Nankai tsunami as 07:24 GMT on 24 December. Kusumoto et al (2020) estimated the origin time of the 1854 Ansei-Tokai tsunami to be 00:30 GMT on 23 December; thus we estimated the time difference between the Ansei-Tokai and Ansei-Nankai tsunamis to be approximately 30.9 h. Our result is in rough agreement with descriptions in historical materials (30-32 h; e.g., Usami, 2003;Central Disaster Management Council, 2005;Matsu'ura, 2017) if the substantial difference in temporal resolution between the seasonal timekeeping system (approximately 2 hours) and the waveform digitization (0.1 h) is taken into account. This finding suggests that information in historical documents can be extremely useful for determining the origin times of historical earthquakes.…”

“…The tide gauge records reported in Omori (1913) have been digitized at 1 min intervals (Kusumoto et al, 2020). The effects on the observed tsunami waveform of filtering due to the structure of the water pipe at the tide gauge station at the time of the earthquake and changes in the hydraulic response are unknown, and there is no information available that allows them to be estimated.…”

“…In this study, we first estimated the origin time of the 1854 CE Ansei-Nankai tsunami by comparing observed and simulated waveforms. Then, we calculated the time difference between the 1854 CE Ansei-Tokai and Ansei-Nankai earthquakes by using our estimated origin time for the Ansei-Nankai tsunami and the origin estimated by Kusumoto et al (2020) for the Ansei-Tokai tsunami and compared the result with historical descriptions of the two earthquakes and tsunamis.…”

“…Kusumoto et al (2020) compared simulated and observed waveforms recorded at San Francisco and San Diego tide gauge stations and concluded that the origin time of the 1854 CE Ansei-Tokai tsunami was 00:30 GMT on 23 December. Similarly, we estimated the origin time of the 1854…”

Time difference between the 1854 CE Ansei–Tokai and Ansei–Nankai earthquakes estimated from distant tsunami waveforms on the west coast of North America

“…Although there are several problems with the observed tsunami waveforms (e.g., the hydraulic filter at the time of observation is unknown), by comparing them with calculated waveforms, they can be used to quantitatively evaluate the tsunami origin time and time difference. In fact, Kusumoto et al (2020) estimated the origin time of the 1854 CE Ansei-Tokai tsunami to be 00:30 on 23 December by comparing the tsunami waveforms observed at stations on the west coast of North America with calculated waveforms. In this study, we first estimated the origin time of the 1854 CE Ansei-Nankai tsunami by comparing observed and simulated waveforms.…”