1. Why Phone Calls Become Congested After a Major Earthquake
When a disaster strikes, calls to the affected area increase rapidly. This volume exceeds the capacity of lines and switching equipment. This is called network congestion. [2]
If this congestion continues, critical communications for rescue and hospitals may fail to get through. Therefore, telecommunications companies intentionally limit the number of outgoing calls by limiting calls. During the Great East Japan Earthquake, mobile phone companies regulated voice calls by up to 70–95%, and fixed-line phones by up to 80–90%. [1]
At the peak, this meant that out of 10 attempts, 7 to 9 were restricted. It is important to note that these figures represent the upper limit during the most intense regulation. They did not apply uniformly across the entire country. [1] Regulations for packet communication, which sends text and data, were either lower than voice regulations or not applied at all. [1]
2. How Broadcasting Reaches Many People at Once While Phones Cannot
Telephones connect one speaker and one listener as a pair. As more people call, the equipment becomes insufficient. Broadcasting, however, involves a station sending radio waves widely, which receivers pick up. The work of the sender does not change regardless of how many people receive the signal. From this perspective, broadcasting is considered less likely to become congested.
This explanation is an inference from the materials. The Ministry of Internal Affairs and Communications White Paper states that emergency earthquake alerts on mobile phones are distributed simultaneously to terminals in specific areas, avoiding the impact of congestion. [4] The principle that "simultaneous distribution is less prone to congestion" can be read from this. [4]
Research papers on disaster broadcasting state that radio is considered a disaster-resilient media because it can be heard anywhere with a receiver and batteries, providing real-time information even when television is unavailable. This assumes the broadcast signal reaches the location. [3]
However, broadcasting stations themselves can stop. During the Great East Japan Earthquake, up to 120 broadcasting stations were confirmed to have stopped transmitting in 11 prefectures, including the six Tohoku prefectures. Of these, 118 were due to power outages. [4] Therefore, remembering that "radio never stops" is not accurate.
3. How the 1964 Niigata Earthquake Showed the Importance of Radio
Papers state that the importance of radio during disasters became widely known to the general public during the 1964 Niigata Earthquake. [3] At that time, television was just beginning to spread. NHK Niigata Broadcasting Station adopted a policy of using radio for those inside the disaster zone and television to convey the devastation to those outside. [3]
The paper introduces the observation by disaster broadcasting researcher Osamu Hiroi that this policy became the basic stance consistent in subsequent disaster broadcasting. [3]
In surveys of commercial radio stations, both AM and FM stations most frequently cited "life information" as a "radio-specific broadcast" during disasters. This suggests a strong awareness of delivering information to people inside the disaster zone. [3]
4. Why Hearing a Familiar Radio Voice Comforted People, Not Just Informed Them
During the Great Hanshin-Awaji Earthquake in 1995, many voices reached radio stations saying they felt relieved to hear the voice of a familiar radio host. [3] In a survey of the three prefectures affected by the Great East Japan Earthquake, there were responses stating that people were saved both materially and mentally by radio. [3]
The paper considers that people may have sought not only useful information but also programs that reminded them of daily life and calm voices. This is the researcher's interpretation and cannot be said to apply to everyone. [3]
Conversely, because it is a voice heard in daily life, a single word during an emergency may be more likely to reach people. [3]
5. How People Listen to Radio in Daily Life, in Cars and at Home
In a survey by the Ministry of Internal Affairs and Communications (October 2024 to March 2025, via the internet, targeting ages 15 to 70), 35.9% of people listened to the radio at least once a month. This equates to about 36 out of 100 people. Those who listened to internet radio at least one day a month were 16.8%. [5] Children were not included in the survey, so these are adult figures.
Listening locations are mostly at home, while commuting or traveling to school, and in cars. The purposes are often "as a habit" or "as background music." The devices used are mostly car audio/navigation systems and smartphones. [5]
Half of radio listeners are in their 50s to 70s, but for internet radio, the proportion of people in their 20s and 30s is higher. [5] This suggests that people listen to radio when their hands and eyes are busy, allowing listening with ears alone.
6. A Simple Experiment: Listening to a Home Radio for 15 Minutes
If you have a radio at home, try turning it on for 15 minutes during breakfast or cleanup. Experience whether you can understand the story without looking at a screen. If it is a battery-powered radio, check with your family whether batteries are inside. If you do not have a radio, a car radio is also fine.
To read the materials, the figures on call regulations come from the Ministry of Internal Affairs and Communications documents on the Great East Japan Earthquake [1], and the division of roles since the Niigata Earthquake and the role of "familiar voices" come from the paper in the Journal of the Japan Society for Safety Engineering [3] as starting points. The mechanism of congestion is explained by NTT Group [2], the number of station shutdowns by the Information and Communications White Paper [4], and current listening habits by the Ministry of Internal Affairs and Communications report summary [5].