Distance from Epicenter

Calculate your distance from an earthquake epicenter and check if you would have felt the shaking.

Calculation

진앙으로부터의 거리가 진동에 미치는 영향

진앙은 단층 파열이 시작되는 지진의 초점(진원) 바로 위 지구 표면의 지점입니다. 지진파는 진원에서 모든 방향으로 방사되며, 기하학적 확산과 감쇠(암석과 토양에 의한 에너지 흡수)로 인해 거리에 따라 진폭이 감소합니다. 이것이 진앙에서 멀어질수록 진동 강도가 감소하는 이유이며, 감소율은 지역 지질, 지진 깊이, 파동 유형에 따라 달라집니다.

체감 반경, 즉 사람들이 지진을 인지할 수 있는 최대 거리는 주로 규모와 깊이에 따라 달라집니다. 얕은 규모 6.0 지진은 200~400 km 떨어진 곳에서도 느껴질 수 있지만, 깊이 300 km의 깊은 규모 6.0 지진은 같은 규모임에도 체감 반경이 더 작을 수 있습니다. 얕은 지진은 지표면 근처에 에너지를 집중시켜 더 강하지만 국지적인 진동을 발생시키고, 깊은 지진은 더 넓지만 덜 강한 범위에 에너지를 분산시킵니다.

핵심 개념

하버사인 공식은 구 위의 두 점 사이의 대원 거리를 계산하며, 이는 진앙 거리를 결정하는 데 사용되는 방법입니다.
지진파 유형 — P파(1차, 압축파)가 가장 먼저 가장 빠르게 도달합니다. S파(2차, 전단파)가 다음으로 도달하며 더 큰 피해를 유발합니다. 표면파(러브파와 레일리파)가 마지막에 도달하지만 가장 파괴적인 에너지를 전달합니다.
USGS ShakeMap과 같은 진도 감쇠 모델은 주어진 규모와 깊이에 대해 수정 메르칼리 진도가 거리에 따라 어떻게 감소하는지 예측합니다.
부지 증폭으로 인해 연약한 토양 위의 먼 장소가 기반암 위의 가까운 장소보다 더 강한 진동을 경험할 수 있습니다.

일반적인 용도

보고된 지진의 체감 범위 내에 해당 위치가 포함되는지 신속하게 판단.
비상 계획 시나리오를 위해 특정 거리에서의 진동 강도 추정.
깊이와 규모가 상호작용하여 다양한 진동 범위를 생성하는 방식 이해.

How to Use

1
Set the Epicenter Coordinates
Enter the earthquake epicenter latitude and longitude, or search by a recent event name. Epicenter coordinates are published by USGS, EMSC, and national seismological agencies within minutes of a significant event.
2
Enter Your Location
Provide your current location as coordinates, a city name, or an address. The tool calculates the great-circle (surface) distance using the Haversine formula.
3
Interpret Your Shaking Estimate
Review your estimated Modified Mercalli Intensity (MMI) and whether the shaking would likely be felt. The estimate uses USGS ShakeMap attenuation relations and assumes average soil conditions.

About

The relationship between distance and ground shaking follows well-defined attenuation functions central to seismic hazard analysis. As seismic waves travel outward from the hypocenter, their amplitude decreases due to geometric spreading (energy distributed over an ever-larger spherical surface) and anelastic attenuation (energy absorbed as heat by imperfectly elastic rock). These effects are codified in Ground Motion Prediction Equations (GMPEs), empirical models derived from thousands of recorded earthquakes that predict median and standard deviation of ground motion parameters—such as peak ground acceleration (PGA) or spectral acceleration—as functions of magnitude, distance, depth, and site class.

ShakeMap, developed by the USGS and now adopted by agencies worldwide, combines recorded ground motions from seismograph networks with GMPE predictions to produce near-real-time maps of shaking intensity across a region. The maps use the Modified Mercalli Intensity (MMI) scale, where MMI I–II represents not-felt or barely-felt shaking, MMI V causes objects to fall from shelves, MMI VII–VIII damages poorly constructed buildings, and MMI X–XII represents near-total structural destruction. ShakeMaps are generated within minutes of significant earthquakes and are used immediately by emergency managers for resource deployment decisions.

For coastal regions, distance from a submarine epicenter carries additional significance beyond ground shaking: earthquake-generated tsunamis. Tsunamis are most efficiently generated by thrust earthquakes on shallow-dipping (< 30°) submarine faults with vertical displacement components greater than roughly 1 meter. The 2004 Sumatra tsunami was triggered 250 km offshore Aceh; wave heights at the coast reached 30 m. Coastal residents within 100 km of a subduction zone should be familiar with the Drop-Cover-Hold guidance for shaking, followed by immediate vertical or inland evacuation upon feeling prolonged shaking lasting more than 20 seconds.

FAQ

How is distance from an earthquake epicenter measured?

Seismologists distinguish between epicentral distance (the surface distance from a location to the point directly above the focus) and hypocentral distance (the straight-line distance to the actual rupture source, accounting for depth). For shallow earthquakes (< 20 km depth), the two values are nearly identical at distances greater than a few kilometers. Epicentral distance is measured along the Earth's surface as the great-circle arc between two points and is expressed in degrees (1° ≈ 111 km) in seismological contexts, or in kilometers for engineering applications. Hypocentral distance is the appropriate quantity for attenuation relations used to predict ground motion.

How far away can an earthquake be felt?

Felt distance depends primarily on magnitude, depth, and regional geology. As a rough guide: a M4.0 may be felt up to 100 km away; a M6.0 up to 400–500 km; a M8.0 can be felt across continental scales exceeding 1,500 km. Deep earthquakes (> 300 km) can be felt at exceptional distances because their waves travel through the mantle with lower attenuation than crustal paths. The 2013 Okhotsk Sea M8.3 deep earthquake (610 km depth) was felt across Russia and as far as Moscow (6,000+ km). Geological structure also plays a role: the central US has lower attenuation than the western US, meaning eastern earthquakes historically felt over larger areas than western events of similar magnitude.

What is the difference between epicenter and hypocenter?

The hypocenter (also called the focus) is the actual point within the Earth where the rupture initiates—where elastic strain energy is first released along the fault. The epicenter is the geographic point on the Earth's surface directly above the hypocenter, obtained by projecting vertically upward. USGS and other agencies report both: epicenter coordinates (latitude/longitude) and focal depth. Depth matters greatly for hazard: a M6.5 earthquake at 5 km depth can be highly destructive, while the same magnitude at 600 km depth may be barely felt at the surface. The 2001 Bhuj earthquake (India) had a shallow depth of 23 km and caused catastrophic damage; in contrast, deep subduction events in the Tonga trench at 600+ km rarely cause surface damage.

Does earthquake depth affect felt shaking?

Earthquake depth has a major influence on the distribution and character of felt shaking. Shallow earthquakes (< 20 km, called 'crustal' earthquakes) concentrate energy near the surface and produce intense, short-duration shaking in a relatively small area. As depth increases, the energy radiates over a larger spherical surface, reducing peak intensities but spreading felt shaking over broader regions. Intermediate-depth earthquakes (70–300 km) in subducting slabs can shake large areas at lower intensities. Very deep earthquakes (> 300 km, 'deep focus') are felt across enormous distances but rarely cause significant damage. The 1994 Northridge M6.7 at 19 km depth caused 57 deaths and US$20 billion in damage; its shallow depth was a key factor in the severity.

Can I determine my distance from an earthquake using a seismograph?

Yes—this is the classical method of locating earthquakes. Seismographs record P-waves (compressional, faster, ~6 km/s in the crust) and S-waves (shear, slower, ~3.5 km/s). The time interval between the P-wave and S-wave arrivals, called the S-P time or Wadati plot, is directly proportional to the distance: distance ≈ S-P time × Vp × Vs / (Vp − Vs). A simple rule of thumb: for every 8 seconds of S-P interval, the earthquake is approximately 80 km away. Three or more seismograph stations allow triangulation of the epicenter. Modern seismic networks with hundreds of stations achieve epicenter location accuracies of 1–5 km within seconds of a significant event.