Fusakichi Omori

1.1. Birth and Early Life

Omori was born on October 30, 1868, in the castle town of Fukui, Echizen Province (present-day Teyori 2-chome, Fukui City, Fukui Prefecture). He was the fifth son of Omori Tōsuke, a lower-ranking samurai, and grew up in a family of eight siblings facing economic hardship. He began his education at the newly established Asahi Elementary School in Fukui. In 1877, his family relocated to Tokyo, where he transferred to Kōritsu Sakamoto School (now Chuo City Sakamoto Elementary School). He later attended Kyōritsu School (now Kaisei High School) in 1881 and entered the Tokyo Imperial University Preparatory School in 1883.

1.2. University Education and Early Career

In 1887, Omori enrolled in the Faculty of Science at Tokyo Imperial University, specializing in physics. He graduated in 1890 and continued his studies in meteorology and seismology under the guidance of the influential British seismologist John Milne, who was a foreign advisor to the university. During this period, Omori also collaborated with Japanese colleagues, including Sekiya Seikei, who had become the first professor of seismology at Tokyo Imperial University in 1880. Sekiya and Omori jointly published the first clear record of a destructive earthquake obtained by their measuring devices at the university. By 1886, Sekiya was appointed chair of seismology and secretary to the Imperial Earthquake Investigation Committee, a body that significantly expanded Japan's seismological network to nearly 1,000 recording stations by the time of his death. In 1891, Omori was appointed assistant to Sekiya, and by 1893, he became a lecturer in seismology at the Imperial University. His early research focused on the aftershocks of the 1891 Mino-Owari earthquake, which laid the empirical foundation for his later formulation of Omori's Law.

1.3. European Study Tour

From 1894 to 1896, Omori undertook a significant study tour in Europe, spending three years in Germany and Italy for advanced research. He also made a brief visit to England in September 1896 on his return journey. This period broadened his scientific perspective and exposed him to cutting-edge research methods. Upon his return to Japan in 1896, following Sekiya Seikei's death on January 9, 1896, Omori was appointed chair of seismology at Tokyo Imperial University and secretary of the Imperial Earthquake Investigation Committee. He was highly proficient in multiple languages, including English, German, Italian, and Japanese, enabling him to maintain extensive correspondence with international seismologists and publish his research papers in all four languages. His leadership roles cemented his position as a guiding figure in Japanese seismology, earning him the title "Father of Japanese Seismology."

2.1. Founder of Japanese Seismology

Fusakichi Omori is widely recognized as a foundational figure in Japanese seismology. After his return from Europe in 1896, he was appointed the second Professor of Seismology at Tokyo Imperial University. He also served for an extended period as the secretary and later president of the Imperial Earthquake Investigation Committee, which was established by the Ministry of Education following the devastating 1891 Mino-Owari earthquake. In these influential roles, Omori provided crucial leadership, laying the scientific and institutional groundwork for the systematic study of earthquakes in Japan, a contribution that earned him the esteemed title "Father of Japanese Seismology."

2.2. Omori's Law (Aftershock Decay)

One of Omori's most significant contributions is the empirical relationship known as Omori's Law, which describes the temporal decay of aftershock frequency following a major earthquake. He first formalized this observation in 1894, based on his detailed studies of the aftershocks from the 1891 Mino-Owari earthquake and other seismic events. The original formulation of Omori's Law states that the number of aftershocks n(t) at time t after the mainshock is inversely proportional to (c+t), where k and c are constants specific to each earthquake sequence.

This law indicates that the rate of aftershock occurrence rapidly decreases over time. For instance, the probability of an aftershock on the day after the mainshock is approximately half that of the first day, and after ten days, it is about one-tenth. This pattern provides a statistical framework for estimating future aftershock probabilities.

In 1961, Japanese seismologist Tokuji Utsu refined Omori's Law, leading to the widely used Utsu-Omori Law, which introduces an additional constant p. This refined law states that n(t) is inversely proportional to (c+t)^p, where p is a constant typically ranging from 0.7 to 1.5, which further adjusts the aftershock decay rate. While Omori's Law is primarily empirical, its theoretical underpinnings have been explored, with interpretations linking it to the deactivation of fault lines after a mainshock and the nucleation process of earthquakes. More recent studies have also shown that solutions to fractional reactive differential equations can yield power-law decay models, including forms consistent with the Utsu-Omori Law.

2.3. The Omori Seismograph

In 1898, Fusakichi Omori developed the Omori seismograph, a groundbreaking instrument that became the world's first continuously recording seismograph. Prior to his innovation, existing seismographs, such as the G.M.E. (Gray-Milne-Ewing) common seismograph, only began recording when their sensors were activated, often missing crucial initial seismic waves like P-waves. Omori's design addressed this limitation by employing a soot-writing method on a drum wrapped with recording paper, which was continuously moved by a spring mechanism. This continuous recording capability allowed for the clear distinction and capture of P-waves, S-waves, and L-waves.

In 1899, Omori formally described his horizontal recording pendulum. With minor modifications by the J&A Bosch Company of Strassburg, it became known as the "Bosch-Omori Seismometer." This instrument was widely distributed globally and formed the backbone of the international seismographic network until after World War II. The enduring impact of his design is evidenced by the fact that the last operating Bosch-Omori seismograph, now functioning independently of the main network, is exhibited at the Ferndale Museum in California. Various improved models, including tremor meters and simple tremor meters, were later developed based on Omori's original design, further solidifying its global influence in earthquake observation.

3.1. Investigations of Japanese Earthquakes

Omori's field research began with a focus on significant Japanese seismic events. The devastating 1891 Mino-Owari earthquake on October 28, 1891, which ravaged Mino and Owari provinces, provided a crucial initial dataset for his studies. The fault lines of this earthquake were meticulously traced by Bunjiro Koto, a colleague at Tokyo Imperial University, who observed a strike-slip fault extending for at least 40 mile on the surface, with the northeast side shifting 3.3 ft ^{(1 m)} to 6.6 ft ^{(2 m)} relative to the other. Some areas exhibited scarps as high as 18 ft to 20 ft. This event, and the data collected on its aftershocks, were instrumental in Omori's formulation of Omori's Law.

Omori also meticulously measured the three principal phases of earthquake motion-preliminary tremors, the main portion, and the end portion-a categorization originally described by John Milne. He consistently visited affected areas after major earthquakes to verify the data collected by his instruments on the ground, demonstrating a rigorous, data-driven approach to seismological investigation.

3.2. International Earthquake Studies

Omori's commitment to understanding seismic impacts extended beyond Japan, leading him to investigate major earthquakes across the globe.

3.2.1. 1906 San Francisco Earthquake Investigation

The 1906 San Francisco earthquake was a pivotal event in Omori's international research. Both Milne-type and Bosch-Omori seismographs worldwide recorded this major seismic event, and seismologists from across the globe converged on Northern California shortly after the disaster. Omori departed Tokyo on May 1, 1906, leading an Imperial committee of distinguished Japanese architects and engineers, including Professors Tatsutaro Nakamura and Toshikata Sano, and architect Magoichi Noguchi. They arrived in San Francisco on May 18, with the dual purpose of studying the earthquake's aftermath and donating a new seismograph to the University of California, Berkeley.

During his approximately 80 days in California, Omori and his colleagues meticulously measured damaged buildings and documented the destruction with photographs. Despite their scientific mission, they encountered instances of anti-Japanese sentiment. Reports indicate they were assaulted on more than one occasion, including an incident on Mission Street where they were attacked by a gang, which some local press outlets, reflecting the prevailing racist climate, reportedly lauded. However, historical records indicate that a boy involved in stoning Dr. Omori was promptly fired from his Post Office job following protests from the Japanese Association of America. Omori, demonstrating remarkable composure and forgiveness, later remarked, "referring to some trouble I had with hoodlums in San Francisco. I was very glad to see that the people of Hawaii did not like to have me treated in that way, but then it did me no injury and I bear no malice. There are hoodlums in all countries. The people of California treated me extremely well and I am very much pleased with my trip."

His extensive fieldwork took him as far north as Humboldt County, California. In Eureka, California, on July 6, 1906, he was mistakenly assaulted by a ruffian who believed him to be a non-union strikebreaking sailor, prompting a prompt apology from the mayor of Eureka. Omori continued his observations south into the Eel River Valley, noting a massive landslide south of Centerville at False Cape. This landslide covered the former coast road and created a new promontory extending into the Pacific Ocean, causing significant damage to local property and buildings. He then meticulously followed the trace of the San Andreas Fault by land south to San Francisco, observing the effects of the earthquake on the ground, buildings, and even large redwood trees, which he noted were split by the shearing motion of the ground.

Omori's visit led to the establishment of the Ferndale Seismographic Station, a collaborative effort between Omori, the University of California (Berkeley), and the United States Coast and Geodetic Survey. This station, located near the Mendocino Triple Junction, supported the installation of a Bosch-Omori Seismograph, which continues to operate independently and is now exhibited at the Ferndale Museum. His detailed observations included studying the directions of ground movement by examining tombstones south of San Francisco and cracks in the walls of buildings like the St. James Hotel in San Jose.

Based on his correlation of damage in Western and Japanese construction, Omori released the first scale of earthquake damage that integrated both instrument readings and observed effects. He described the faulting in California as parallel to the strike of the fault, caused by shear stresses on the plane of fracture. Following his recommendations, Omori seismographs were rapidly installed across Northern California, and a comprehensive list of aftershocks to the San Francisco earthquake was compiled and published. Omori returned to Japan on August 4, 1906.

3.3. Volcanic Seismology

Omori's scientific interests extended to volcanic seismology, a field he continuously researched from his early papers on the 1893 eruption of Mount Azuma until his death. He meticulously described various types of volcanic earthquakes, drawing data from regular eruptions of Mount Asama in central Japan, the 1910 eruption of Mount Usu, and the 1914 Sakurajima eruption.

During the 1910 Mount Usu eruption, Omori installed his prototype seismograph in Sōbetsu Town, conducting detailed observations that led to the world's first recording of volcanic tremors, significantly advancing volcanology. In 1911, he expressed confidence that "prediction of large eruptions is not terribly difficult in some cases," and actively proposed the establishment of permanent volcanic observatories to facilitate eruption forecasting, publishing a paper on Mount Usu.

His foresight was again demonstrated during the 1914 Sakurajima eruption. On the morning of January 12, having received reports of increasing seismic activity around Sakurajima, he was preparing to issue a warning telegram when the eruption commenced. Following the eruption, on January 16, he inspected Sakurajima from the sea and issued a crucial statement that Kagoshima City was not in immediate danger, effectively restoring calm to the then-chaotic city.

Internationally, Omori collaborated with Thomas Jaggar of the Massachusetts Institute of Technology, who was planning a volcanic observatory on the Big Island of Hawaii. Omori designed the foundations and seismograph emplacement for the Whitney Laboratory of Seismology, Building 29, near Volcano House, which is now part of the Hawaiian Volcano Observatory. In 1912, he shipped two instruments-an Omori-type Horizontal Tromometer and a seismograph-to Hawaii for installation on these specially built foundations. A year later, MIT further donated two Bosch-Omori seismographs to the Hawaiian Volcano Observatory, underscoring the global recognition of Omori's instrumental designs.

3.4. Earthquake Engineering and Disaster Impact

Omori's work extended significantly into earthquake engineering and the study of disaster impact. As early as 1889, he collaborated with John Milne on experiments at the Engineering College of the University of Tokyo, investigating how horizontal ground motion could overturn and fracture brick and other types of columns. This research was particularly pertinent during the Meiji Restoration, as Japan was undergoing a modernization drive that involved replacing traditional light wooden structures with heavier red brick buildings and iron bridges, a shift that raised concerns about seismic vulnerability.

Omori continued this pioneering research, becoming recognized as the first to systematically study the effects of earthquakes on man-made structures through the use of shaking tables. He conducted controlled experiments and compared these results with observations from actual earthquakes, providing invaluable data for seismic-resistant design. His investigations consistently highlighted the critical link between building resilience and casualty rates. For instance, following the devastating 1908 Messina earthquake, Omori observed the immense loss of life, estimating around 75,000 people perished, and critically noted that 99% of these fatalities were due to houses not being constructed to withstand seismic forces. This underscored his strong advocacy for robust building codes and effective disaster mitigation strategies to reduce societal vulnerability to earthquakes.

4.1. Research Methodology and Scientific Approach

Fusakichi Omori's academic thought was characterized by a rigorous, empirical approach to seismological research. He emphasized meticulous data collection, both through instrumental recordings and extensive fieldwork. He systematically measured the three principal phases of earthquake motion-preliminary tremors, the main portion, and the end portion-a framework initially outlined by John Milne. Crucially, Omori would visit affected areas after major earthquakes to ground-verify the data collected by his instruments, ensuring the accuracy and practical relevance of his findings.

His development of the Omori seismograph in 1898 exemplifies his commitment to improving data acquisition. This instrument, the world's first continuously recording seismograph, allowed for the clear distinction of P-waves, S-waves, and L-waves, overcoming the limitations of previous models that often missed initial seismic phases. The widespread adoption of his seismograph, both in Japan and internationally, facilitated a global network of continuous seismic observation.

Omori's proficiency in English, German, Italian, and Japanese enabled him to maintain extensive correspondence with a broad network of international seismologists. This linguistic versatility fostered significant collaborative efforts, allowing him to share his research findings globally and integrate diverse perspectives into his own work, thereby advancing the field of seismology on an international scale.

4.2. Views on Earthquake Prediction

Omori held a cautious and statistically grounded stance on earthquake prediction, particularly concerning major seismic events. While he recognized the imperative for disaster preparedness, he was wary of public panic induced by unverified forecasts. In 1905, when his assistant professor, Akitsune Imamura, published an article in the magazine "Taiyo" warning of a potential major earthquake in Tokyo within 50 years, the media's sensationalized reporting turned it into a significant social issue. Omori, fearing the societal disruption that such a warning could cause without sufficient scientific backing, publicly dismissed Imamura's article as baseless, despite his own understanding of the need for earthquake countermeasures.

However, his views on volcanic eruption prediction were more optimistic. In 1911, based on his detailed observations of volcanic activity, he stated that "prediction of large eruptions is not terribly difficult in some cases," and actively proposed the establishment of permanent volcanic observatories to facilitate eruption forecasting. This distinction highlights his empirical approach: while he acknowledged the statistical nature and inherent difficulties in precise earthquake forecasting, he saw greater potential for prediction in volcanic seismology where more direct precursors could be observed and systematically monitored.

5.1. Debates with Contemporaries

A notable debate in Omori's career involved his contemporary, Akitsune Imamura, an assistant professor in the same department. In 1905, Imamura published an article in the magazine "Taiyo" warning of a high probability of a major earthquake striking Tokyo within the next 50 years and urging preparedness. This article was sensationalized by newspapers, causing considerable public alarm and becoming a significant social issue. While Omori recognized the importance of disaster prevention, he was deeply concerned about the potential for social confusion and panic that such a public warning, lacking immediate scientific certainty, could trigger. Consequently, he publicly rejected Imamura's predictions as unfounded, leading to a prominent scientific and public controversy known as the Omori-Imamura controversy. This disagreement underscored differing philosophies on the communication of scientific forecasts and the responsibility of scientists to society.

5.2. Societal Context and Incidents

Omori's scientific endeavors were not isolated from broader societal contexts, and he encountered various public reactions and incidents throughout his career. During his investigation of the 1906 San Francisco earthquake, he and his Japanese colleagues faced instances of anti-Japanese sentiment. They were reportedly assaulted on multiple occasions, including an attack on Mission Street by a gang, which some local press outlets, reflecting the prevailing racist climate, reportedly lauded. However, historical records indicate that a boy involved in stoning Dr. Omori was promptly fired from his Post Office job following protests from the Japanese Association of America. Despite these incidents, Omori maintained a remarkably composed and forgiving attitude, publicly stating, "referring to some trouble I had with hoodlums in San Francisco. I was very glad to see that the people of Hawaii did not like to have me treated in that way, but then it did me no injury and I bear no malice. There are hoodlums in all countries. The people of California treated me extremely well and I am very much pleased with my trip." Further north in Eureka, California, he was mistakenly assaulted by a ruffian who mistook him for a non-union strikebreaking sailor, leading to an immediate apology from the city's mayor.

His interactions with the public also demonstrated his commitment to societal well-being. For example, following the 1914 Sakurajima eruption, his swift assessment and public announcement that Kagoshima City was not in immediate danger played a crucial role in calming widespread panic and restoring order. These episodes highlight the intersection of Omori's scientific work with the social realities and public perceptions of his time.

6.1. Personal Life

Fusakichi Omori was the fifth son in a family of eight siblings, born to Omori Tōsuke, a lower-ranking samurai. His early life was marked by economic hardship, which he overcame through his dedication to education and scientific pursuit. While historical records primarily focus on his professional achievements, they suggest a life dedicated to his research and public service.

6.2. Final Years and Death

In the fall of 1923, Fusakichi Omori traveled to Australia to attend the Second Pan-Pacific Science Congress. While there, at the Riverview College Observatory in Sydney, he and its director, Edward Pigot, observed a seismograph recording the devastating 1923 Great Kantō earthquake. This catastrophic event, which struck on September 1, 1923, annihilated Yokohama and Tokyo, claiming approximately 140,000 lives and leaving 1.9 million people homeless.

Upon learning the scale of the disaster in Japan, Omori cut short his trip. He returned to Japan from Melbourne, Australia aboard the Tenyo Maru on October 4, 1923. Shortly after his return, he was diagnosed with a severe brain tumor and was immediately admitted to the university hospital. Just days before his passing, he was honored with the Order of the Sacred Treasure from the Imperial Court, a testament to his distinguished service. Fusakichi Omori died at the age of 55 on November 8, 1923. His grave is located in Tama Cemetery.

7.1. Scientific Legacy

Fusakichi Omori's scientific legacy is profound and enduring, marking him as a pivotal figure in the history of seismology and earthquake engineering. He is widely celebrated as one of the principal founders of modern seismology in Japan, serving as the second chairman of seismology at Tokyo Imperial University and as president of the Imperial Earthquake Investigation Committee. His most renowned contribution, Omori's Law, an empirical formula describing the temporal decay of aftershock frequency, remains a fundamental concept in seismology, continuously refined and applied in modern earthquake analysis.

The Omori seismograph, his innovative design for a continuously recording instrument, revolutionized seismic observation. Its widespread adoption, particularly as the Bosch-Omori seismometer, formed the backbone of the global seismographic network until well after World War II, demonstrating its reliability and accuracy. Furthermore, Omori was a pioneer in earthquake engineering, being the first to systematically study the effects of earthquakes on man-made structures through the use of shaking tables and by comparing experimental results with real-world seismic damage. His work in volcanic seismology, including the world's first recording of volcanic tremors and his advocacy for permanent volcanic observatories, also contributed significantly to the understanding and prediction of volcanic activity. His foundational laws, instrumental designs, and rigorous empirical methodology continue to influence seismic research and disaster mitigation efforts worldwide.

7.2. Commemorative Efforts

Fusakichi Omori's contributions are commemorated in various ways, ensuring his legacy continues to be recognized. In his birthplace of Teyori 2-chome, Fukui City, a bronze statue of Omori stands in Teyori Park, alongside a relief that depicts the Omori seismograph, symbolizing his pioneering work in the field. His life and scientific achievements are also chronicled in numerous biographies and academic studies, including "The Man Who Created Seismology: Fusakichi Omori" and "The Two Men Who Predicted the Great Kanto Earthquake: Fusakichi Omori and Akitsune Imamura," which continue to highlight his impact on Japanese and global science. These commemorative efforts underscore his enduring recognition as the "Father of Japanese Seismology" and a crucial figure in the history of disaster science.