A Soil Base disaster
In the Ansei Edo earthquake, the most important causal factor in determining the severity of ground motion, and therefore destruction, was the soil base. Ground motion was least severe in upland areas such as the Yamanote Highlands. It was more severe but still relatively moderate in lowland areas of the city built on solid ground. Such areas typically experienced a level of five using the JMA seismic intensity scale (shindo). Ground motion, destruction, fires, and loss of life were most severe (level six) in areas built on unconsolidated fill. In other words, former wetland areas filled in with dirt or debris after Edo became Japan's de facto capital suffered dramatically more destruction than other parts of the city.
Owing to a phenomenon called material amplification, ground motion increases in severity as the base soil becomes softer. Alluvial soil amplifies seismic waves compared with sedimentary rock, and silt or unconsolidated fill produces the greatest degree of amplification. An increase in wave amplitude, a vertical shift in the path of seismic waves, and basement rock trapping seismic waves are the reasons for this amplification. Liquefaction is also common in areas built on unconsolidated fill. The 1995 HanshinAwaji (Kobe) earthquake was so destructive “because the strongest shaking was squeezed into a 3km wide plain between mountains and Osaka Bay” and many structures were built “on harbor fill.” Moreover, in the 1923 Great Kantō Earthquake, “disturbances in alluvial material were particularly marked” to such a degree that in one area, “potatoes were extruded onto the ground” from the shaking of soft soil. The basic geophysical principle that ground motion is most severe with soft, unconsolidated soil is what made the Ansei Edo earthquake primarily a “soil base disaster” (jiban saigai), to use Kitahara Itoko's term. One of the few studies of the Ansei Edo earthquake in English is Andrew Markus' fine essay, “Gesaku Authors and the Ansei Earthquake of 1855.” A work based in large part on a close and insightful reading of primary sources, Markus' essay has been influential as a reference point for comparisons of the Ansei Edo earthquake with later seismic disasters. Unfortunately, Markus' description of the damage, while not incorrect as far as it goes, is misleading:
Whether because of greater proximity to the epicenter of the earthquake, or softer alluvial soil, or whether because of a higher residential density, poorer quality of building construction, and a lack of open spaces for refuge, the plebian areas closest to the Sumida River were the most severely affected. Destruction was greatest in the Shitamachi (downtown) districts of Honjo, Fukagawa, Kameido, Asakusa. In contrast, Yamanote (uptown) districts like Yotsuya, Akasaka, and Ichigaya, topographically as well as economically superior, were far less susceptible to the worst effects of the catastrophe. While the Ansei earthquake deeply affected all sectors of the population and all facets of urban life, its 'social bias' against the least affluent classes of citizens is noteworthy.
Markus does indeed identify all the significant factors (aside from random chance) that determined degrees of destruction, but without prioritizing them. Moreover, in an attempt to demonstrate socio-cosmic bias against the “least affluent classes,” Markus leaves out a major component of the picture, namely the devastation of Daimyo Lane (Daimyō Kōji) and some other elite warrior neighborhoods. The reality on the ground did not conform so neatly to socioeconomic levels.
Markus' characterization of the overall damage pattern has influenced other studies. In his book on the Nōbi earthquake, for example, Gregory Clancey drew comparisons with 1855. Relying substantially on Markus, Clancey described the damage pattern as “disproportionately concentrated in the residential districts of the lower town. The great temples and shrines, and the residences of the Shogun, daimyō, and samurai had been comparatively less affected than those of the artisan and merchant classes. . . . Tokugawa elites had also commandeered relatively high, rocky ground for themselves away from the alluvial plains where the effects of earthquakes were most severe, but where common people often had no choice but to cluster and build.” In effect, Clancey logically extends Markus' description of the overall damage pattern to claim that elites suffered significantly less than commoners did. Moreover, this claim became part of Clancey's assessment of the 1891 Nōbi Earthquake: “That the physical infrastructure of the state or other elites (such as the new industrial concerns) should be particularly susceptible to damage from natural disaster was arguably unusual in the Japanese experience, and a reversal of the age-old order in which suffering had been more clearly demarcated along lines of wealth and power.” The notion that elites fared comparatively well in the Ansei Edo earthquake is in part a function of sources and data. We have very accurate data on commoner death and destruction owing to systematic surveys orchestrated by the City Magistrate and extensive essays, diaries, and other written accounts. Warriors wrote a few earthquake accounts, but most accounts were the products of townspeople. Deaths in military households were approximately as numerous as those in civilian households, but the military data is much more dispersed and difficult to interpret.
Another reason for a tendency to focus on the earthquake as a disaster mainly affecting townspeople of modest means was the general Meiji-era debates over architecture that Clancey analyzes in detail. Advocates of native, wood-based construction, as opposed to foreign, brick-and-mortar construction, tended to stress that well-built wooden structures have historically performed well in earthquakes. Because 1855 was the most recent test case, they emphasized that only shoddy structures in poor neighborhoods suffered severe damage. For example, in the context of debates about the best type of construction for the imperial palace, government architect and wood advocate Tachikawa Tomokata argued that in 1855, “'only the low degree houses' had fallen, while those 'above the middling level' sustained only the slightest damage.” This Meiji-era concern with construction quality reinforced a view of the Ansei Edo earthquake as an event whose destruction neatly divided along socioeconomic lines. It also contributed to the notion that traditional, premodern construction techniques evolved in response to earthquakes and were somehow more resistant to violent shaking than are modern structures. This claim is generally inaccurate. Indeed, today's scholars need to make adjustments when using damage to structures in estimating the level of historical earthquakes on the JMA seismic intensity scale (whose current iteration dates from 1995), because across all categories of construction, premodern structures were weaker than those of contemporary or recent vintage. As Clancey and Markus point out, earthquake damage indeed differed significantly along a divide of highlands versus lowlands. This high versus low topographical division, however, did not closely correspond to economic categories or the formal status categories of warrior versus commoner. Most commoners did live in lowland areas, but not all commoner neighborhoods were located on a poor soil base. Warriors occupied both high and low areas. The mansions of Matsudaira Buzen-no-kami and Hotta Bitchū-no-kami, for example, were built in Kanda's Ogawamachi on unconsolidated fill atop what was once the Ogawa Marsh. It might well have been the worst place in Edo to erect a building, and these two daimyō did not even attempt to rebuild in that location after the earthquake obliterated their residences.
The most prestigious district in Edo was the area within the outer castle precincts (o-kuruwa uchi), corresponding to present-day Marunouchi business district and parts of Ōtemachi. Most of this area was located atop a poor soil base. Indeed, much of it had been marsh or open water, the Hibiya Cove, prior to 1608. Classified as “foundational” (kaname), the area was the location of elite fudai daimyō residences and major bakufu offices such as the Hyōjōsho (the highest judicial organ), one of two Kanjōsho (treasury offices; the other was within the castle), and both City Magistrate
offices. The area was the heart of Tokugawa authority outside of Edo Castle itself, and it experienced severe, dramatic damage. According to Noguchi Takehiko, it was as if the earthquake “volitionally” targeted the center of bakufu power. The death rate in Daimyo Lane was unusually high (736), and Nihonbashi neighborhood head Saitō Gesshin provided a vivid account of the fate of this area: “The mansions of the domain lords came crashing down all at once. Right away, fires broke out here and there, and the sound as large timbers burnt and tiles collapsed resounded through heaven and earth—a repeat of the roar of the earthquake.” The passage continues with an extensive listing of the destroyed mansions.
Much of this elite zone faced a commoner district located just across the outer moat of Edo Castle and separated by the bridges Gofukubashi and Kajibashi. In terms of today's landmarks, the commoner district ran along present-day Chūō-dōri between Nihonbashi and Kyōbashi. This district suffered modest damage, mostly to storehouses. By contrast, just across the moat, the warrior side was a mass of collapsed buildings, fires, and general confusion. In 1600, only yesterday in geologic time, this devastated zone was Hibiya Cove. The nearby commoner neighborhood was located
Map 2 Produced by Jeffrey Smits, Cherokee Drafting Specialists. on solid ground—what in 1600 was an outcropping of land known as Edo Maejima, a wave-eroded plateau. The inner moat of Edo Castle marked the sixteenth-century boundary between land and sea. The Wadakura Gate, for example, was once the site of an underground storehouse (kura) that extended under Hibiya Cove. The Aizu mansion was located just to the east of this gate, atop the former cove, and the earthquake destroyed it. In terms of today's landmarks, Tokyo Station is on solid ground, and to the east of it is the former Edo Maejima. Yūrakuchō Station and Shinbashi Station are atop the former Hibiya Cove (map 2).
The landscape of Edo underwent a major transformation during the first decade of the Tokugawa bakufu. Beginning in 1603, a small army of workers from several domains began transporting dirt from nearby Kandayama to fill in Hibiya Cove. The newly created land became prime real estate. It was as if the 1855 earthquake shook the boundaries of an older, forgotten Edo back into sight, tracing the contours of pre-bakufu times via dramatically differing patterns of destruction. Jōtō Sanjin, the pen name of Iwamoto Sashichi, described leaving his residence and crossing Gofuku Bridge to enter Daimyo Lane and then the Wadakura Gate. After explaining that this area shook especially hard, he characterized it repeatedly as “fire earth” (kachi), possibly a term he created (it appears in the Classic of Changes in connection with the thirty-fifth hexagram). Fires in the Ansei Edo earthquake tended to correspond closely to the areas of most severe shaking, and according to a young police official at the scene, “Daimyo Lane burned intensely everywhere.” One additional factor that made the fires in Daimyo Lane especially dramatic was that several daimyō were in charge of the recently constructed offshore artillery batteries. Their mansions contained stores of potassium nitrate (saltpeter), which ignited in the flames.
Sanjin's account of the damage summarized the situation by explaining that upland areas shook mildly, whereas lowland areas (including Fukagawa, Honjo, and the castle precincts) shook severely. “This can be called a principle of nature,” he concluded. Other earthquake accounts made a similar point. Record of the Times (Jifūroku), for example, after describing the devastation in several low-lying areas, says, “Indeed, highland areas shook lightly and damage to structures as well as deaths were few.” Nearly every comprehensive account of the damage described the extreme devastation in both commoner and elite areas built on soft ground. In most instances, the authors of these accounts regarded elevation as the key variable, not soil base. Although upland neighborhoods were all built on a firm base, the soil base of lowland areas varied greatly, as we have seen.
At least one writer, however, precisely identified the relevant variables owing to his knowledge of Edo's history. After a detailed accounting of damage in the downtown areas, Mishima Masayuki explains, “Since the building of Edo Castle, this was an unprecedented shaking. Starting with the gosanke, and extending to daimyō, bannermen, gokenin, retainers, peasants, towns-people, and everyone else, very few were able to escape this disaster.” He also speculates that daimyō, bannermen, bakufu retainers, and other warriors would likely seek to conceal casualties in their households. “Based on what I witnessed,” Masayuki concludes, “amidst the collapses of residences in Daimyo Lane, there must have been many cases of injury and sudden death.” He continues his analysis, explaining that most daimyō household members live in two-story, long houses with limited exits, especially for the women of the household. Overall, Masayuki estimates casualties in military households as twice those of the townspeople. With greater precision than Sanjin, Masayuki explains the exact reason why the earthquake devastated areas such as Fukagawa, Honjo, and Daimyo Lane so severely: “Places built on land that long ago was created from the sea shore naturally shake more severely in an earthquake.”
Although the quality of the soil base was the most important variable in determining rates of death and destruction for everyone, population density and quality of construction were significant secondary factors. Arguably, the worst location for someone when the shaking started would have been the upper story of a Shin-Yoshiwara brothel. Also dangerous would have been a rented back-alley shop in the Tomigaoka Hachiman area of Fukagawa. Residents of the same neighborhood in comparatively spacious shops facing a main street were more likely to have survived. Sakuma Chōkei was a nineteen-year-old police official on duty when the earthquake struck. He described conditions in the back alleys in part as follows: “In the neighborhoods, those who lived in alleyway shops panicked to escape through the narrow paths. Their steps broke the drain-covering boards, causing sprained ankles or the inability to move. Many children were trampled to death. There were numerous instances of injuries from falling roof tiles.” Undoubtedly, the people who endured such harrowing conditions and survived would have been inclined to imagine levels of death and destruction in Edo much higher than the statistics collected at the time indicated. These statistics came from two surveys ordered by the City Magistrate and carried out by the neighborhood heads. The City Magistrate was able to act quickly after the earthquake struck. The shaking destroyed or damaged nearly every mansion in Daimyo Lane and major bakufu offices such as the Hyōjōsho and the lower Kanjōsho. Almost inexplicably, however, offices connected with city governance and relief survived with relatively little harm. After a lengthy listing of damage to elite mansions, Saitō Gesshin pointed out that many of the military households in the Marunouchi area were making do in makeshift, temporary structures. In a separate entry, he next pointed out that the northern and southern City Magistrate offices were unharmed except for damage to long houses attached to the northern Machibugyō. Moreover, Gesshin explained that the three offices of the Machidoshiyori (city administrators below the City Magistrate and above the neighborhood heads) were undamaged. Especially significant, the office of the Machigaisho (sometimes spelled Machikaisho), Edo's emergency relief agency, also escaped serious damage. Its grain storehouses were badly damaged, but they did not catch fire, and the grain was available for relief efforts. It was as if the cosmic forces had struck the center of bakufu power but spared precisely those parts of the government in a position to provide relief to the townspeople.
-  According to Edward A. Keller and Nicholas Pinter, “The potential for amplification of surface waves to cause damage was again demonstrated with tragic results in the 1989 Mw 7.2 Loma Prieta (San Francisco) earthquake, when the upper tier of the Nimitz Freeway in Oakland, California, collapsed, killing forty-one people (fig. 1.16). Collapse of the tiered freeway occurred on a section of roadway constructed on bay fill and mud. Where the freeway was constructed on older, stronger alluvium, less shaking occurred and the structure survived. Extensive damage was also recorded in the Marina District of San Francisco (fig. 1.17), primarily in areas constructed on bay fill and mud, including debris dumped into the bay during the cleanup following the 1906 earthquake.” See Keller and Pinter, Active Tectonics: Earthquakes, Uplift, and Landscape, 2nd ed. (Upper Saddle River, NJ: Prentice Hall, 2002), 21–23 (figures on 24).
-  Susan Elizabeth Hough, Earthshaking Science: What We Know (and Don’t Know) about Earthquakes (Princeton, NJ: Princeton University Press, 2002), 80–83.
-  Bruce A. Bolt, Earthquakes (New York: W. H. Freeman and Company, 1993, fifth printing, 1997), 266.
-  Bolt, Earthquakes, 132.
-  Kitahara Itoko, ed., Nihon Saigaishi (Yoshikawa kōbunkan, 2006), 254.
-  Andrew L. Markus, “Gesaku Authors and the Ansei Earthquake of 1855,” in Dennis Washburn and Alan Tansman, eds., Studies in Modern Japanese Literature (Ann Arbor: Center for Japanese Studies, University of Michigan, 1997), 55.
-  Gregory Clancey, Earthquake Nation: The Cultural Politics of Japanese Seismicity, 1868–1930 (Berkeley: University of California Press, 2006), 123, 220.
-  Ibid., 123.
-  Most major studies of the Ansei Edo earthquake from the 1990s onward discuss military casualties in some detail. The most extensive treatment, including discussion of issues in interpreting different types of data, is Chūō bōsai kaigi, 1855 Ansei Edo jishin hōkokusho (Fuji sōgō kenkyūsho, 2004), especially Kitahara Itoko, “Saigai to Shakaizō,” 43–59. See also the detailed tables and charts in this volume, 95–122. Also valuable is Noguchi Takehiko, Ansei Edo jishin: Saigai to seiji kenryōku (Chikuma shobō, 1997), 72–73, 108–110.
-  Clancey, Earthquake Nation, 55.
-  Nakamura Misao, “Ansei Edo jishin,” in Chūō bōsai kaigi, 1855 Ansei Edo jishin hōkokusho, 2–5.
-  Kitahara, “Saigai to Shakaizō,” 51.
-  Noguchi, Ansei Edo jishin, 71, 73, 75 (map), 91–92. For an extended discussion of the interconnections between topography and political power with respect to the destruction of prime bakufu real estate, see 71–128. Subsequent studies have reinforced many of Noguchi’s main points. See Nakamura Misao, Matsuura Ritsuko, Kayano Ichirō, Karakama Ikuo, and Nishiyama Akihito, “Ansei Edo jishin (1855/11/11) no Edo shichū no higai,” Rekishi jishin 18 (2002): 77–96, and Nakamura, Kayano, and Matsuura, “Ansei Edo Jishin no shutoken de no higai,” Rekishi jishin 19 (2003): 32–37.
-  Saitō Gesshin, Ansei itsubō bukō chidō no ki, in Edo sōsho kankō kai, eds., Edo sōsho 9 (Edo sōsho kankōkai, 1917), 2.
-  For a discussion of these geographical details, see Noguchi, Ansei Edo jishin, 73–81, 97–98. Especially helpful are the maps on 75, 79, and 99. Also helpful for visualizing the differences between pre-1600 Edo and post-1600 Edo are the two maps on the inside cover of Akira Naito, Edo, the City That Became Tokyo: An Illustrated History, Kazuo Hozumi, illus., H. Mack Horton, trans. (Kodansha, 2003).
-  See Naito, Edo, 36–37, for more details. See also Tsuji Yoshinobu, Sennen shinsai: Kurikaesu jishin to tsunami no rekishi ni manabu (Daiyamondo sha, 2011), 88–90, 182, for a useful discussion and map of daimyō mansions and Hibiya Cove.
-  Noguchi, Ansei Edo jishin, 98.
-  “Yabure mado no ki,” in DNJS, vol. 2 (otsu), 559–560.
-  Sakuma Chōkei, “Ansei daijishin jikken dan,” in NJS, vol. 5, supplement 2, part 1, 470.
-  Noguchi, Ansei Edo jishin, 95–96.
-  “Yabure mado no ki,” in DNJS, vol. 2 (otsu), 561.
-  “Jifūroku,” in DNJS, vol. 2 (otsu), 538.
-  “Nai no nochimigusa,” in DNJS, vol. 2 (otsu), 573–574.
-  “Nai no nochimigusa,” in DNJS, vol. 2 (otsu), 574. See also Noguchi, Ansei Edo jishin, 72–73, for discussion of another source reaching precisely the same conclusions, and Kitahara Itoko, Jishin no shakaishi: Ansei daijishin to minshū (Kōdansha, 2000), 109–111. See also Tsuji, Sennen shinsai, 88–90.
-  “Nai no nochimigusa,” in DNJS, vol. 2 (otsu), 572.
-  For discussions of secondary and tertiary factors such as population density, construction methods, access to open spaces, and so forth, see Kitahara, “Saigai no shakaizō,” 53, 60–64, and Kitahara Itoko, Jishin no shakaishi, 50–79.
-  “Ansei daijishin jikken dan,” in NJS, vol. 5, supplement 2, part 1, 473–474. See also Kitahara, “Saigai no shakaizō,” 64.
-  Saitō, Ansei itsubō bukō chidō no ki, 4. See also Noguchi, Ansei Edo jishin, 33–34, 148–149.