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Epicenter

In seismology, the epicenter is the point on the Earth's surface directly above the hypocenter (also known as the focus), which is the subsurface location where an earthquake's rupture begins.^[1] This surface point marks where seismic waves first emerge and is often associated with the most intense ground shaking, though the actual distribution of shaking can vary due to local geology and fault characteristics.^[2] Epicenters play a crucial role in earthquake analysis and hazard assessment, as they help scientists map seismic events and predict potential impacts on populated areas.^[3] They are determined through triangulation using data from multiple seismograph stations worldwide; the time differences in when seismic waves arrive at each station allow for calculating distances, which are plotted as circles on a map, with their intersection revealing the epicenter's location.^[4] Organizations like the U.S. Geological Survey (USGS) routinely report epicenter coordinates for major earthquakes to aid in emergency response and research into tectonic activity.^[5] While the term originates from geological contexts, "epicenter" is also used metaphorically to describe the central point of any major event or disturbance, such as the epicenter of a political crisis or epidemic.^[6]

Definition and Basics

Core Definition

In seismology, the epicenter is defined as the point on the Earth's surface that lies directly above the hypocenter, the subsurface location where an earthquake's rupture begins.^[7] This surface point is determined by projecting the hypocenter vertically upward through the Earth's crust to the ground level.^[8] The epicenter itself is not the site of energy release during an earthquake; rather, it serves as a geographic reference on the surface corresponding to the actual three-dimensional origin of seismic waves beneath the ground.^[5] This distinction emphasizes that the epicenter is a two-dimensional projection, useful for mapping and analysis, while the hypocenter represents the precise volumetric focus of the event.^[7] Notable examples illustrate this concept in major historical earthquakes. For the 1906 San Francisco earthquake, the epicenter was located in the Pacific Ocean approximately 2 miles west of the city, directly above the subsurface rupture along the San Andreas Fault.^[9] Similarly, the 1964 Great Alaska Earthquake had its epicenter in the Prince William Sound region, about 75 miles (120 km) east of Anchorage, marking the surface projection of a massive subduction zone rupture.^[10]

Relation to Hypocenter

The epicenter represents the geometric projection of the hypocenter onto the Earth's surface, specifically the point where a line drawn from the hypocenter perpendicular to the surface—or more precisely, along the radial direction from the Earth's center—intersects the surface. This vertical or radial projection defines the epicenter as the nearest surface location to the subsurface rupture initiation point, distinguishing it from the hypocenter, which is the actual three-dimensional origin of the earthquake within the Earth.^[11]^[7]^[12] The depth of the hypocenter significantly influences the relevance and interpretability of the epicenter in assessing earthquake impacts. In shallow earthquakes, typically occurring at depths less than 70 km in crustal settings, the epicenter closely approximates the area of maximum surface shaking intensity, as seismic waves travel a short distance to the surface with minimal energy loss. Conversely, for deep earthquakes exceeding 300 km, such as those in subduction zones where one tectonic plate descends beneath another, the epicenter becomes less indicative of damage patterns, since waves must propagate through greater thicknesses of rock, attenuating energy and potentially causing widespread but less intense shaking far from the projected surface point.^[13]^[14]^[15] In terms of coordinate representation, the epicenter is typically specified using two-dimensional geographic coordinates of latitude and longitude on the Earth's surface, facilitating mapping and communication of surface locations. The hypocenter, however, requires three-dimensional coordinates, incorporating latitude, longitude, and depth below the surface, to fully capture its position within the Earth's interior. This distinction arises from the need to account for the subsurface geometry in seismological analysis.^[16] Accounting for the Earth's spherical geometry, the direct projection of the hypocenter to the epicenter follows a radial line from the planet's center through the hypocenter to the surface, rather than a purely local vertical line that might apply on a flat plane. This radial projection ensures accuracy over global scales, as deviations from sphericity are negligible for most seismic events. A simple conceptual diagram would depict Earth as a sphere with a point (hypocenter) inside at a certain depth along a radius, extended outward to intersect the spherical surface at the epicenter, illustrating how the two points align along the same radial vector.^[12]^[16]

Determination Methods

Instrumental Determination

Instrumental determination of earthquake epicenters relies on global and regional seismograph networks that continuously monitor seismic activity to record the arrival times of primary (P) and secondary (S) waves generated by earthquakes. Organizations such as the United States Geological Survey (USGS) operate extensive networks, including the Global Seismographic Network (GSN) and the Advanced National Seismic System (ANSS), which consist of hundreds of high-fidelity seismometers deployed worldwide to detect and characterize seismic events. These instruments capture the ground motions caused by P-waves, which travel faster through the Earth (typically 5-8 km/s in the crust), followed by slower S-waves (typically 3-4.5 km/s), allowing scientists to analyze the timing differences for location purposes.^[17]^[18] The primary method for pinpointing the epicenter is triangulation, which involves calculating the epicentral distance from multiple seismic stations and finding the point where these distances intersect on the Earth's surface. For each station, the time lag between P- and S-wave arrivals, denoted as Δt, is used to estimate the distance d to the epicenter. This process begins with the basic physics of wave propagation: the travel time for the P-wave is t_p = \frac{d}{V_p}, where V_p is the P-wave velocity, and for the S-wave, t_s = \frac{d}{V_s}, where V_s is the S-wave velocity (with V_p > V_s). The observed time difference is then \Delta t = t_s - t_p = d \left ( \frac{1}{V_s} - \frac{1}{V_p} \right ) = d \frac{V_p - V_s}{V_p V_s}. Solving for d yields the epicentral distance formula:

d = \Delta t \cdot \frac{V_p V_s}{V_p - V_s}

Assuming average crustal velocities (e.g., V_p \approx 6 km/s and V_s \approx 3.5 km/s), this simplifies to an empirical relation where d is approximately 8 km per second of Δt, though velocity models are refined using travel-time tables for accuracy. By applying this to data from at least three stations, circles of radius d are drawn around each station on a map; their intersection defines the epicenter. Modern algorithms, such as least-squares inversion implemented in software like HypoInverse or NonLinLoc, iteratively adjust the location to minimize residuals between observed and predicted arrival times across the network.^[19]^[20]^[21] Since the 2000s, advancements in geodetic technologies have enhanced the precision of epicenter locations by integrating Global Positioning System (GPS) and satellite interferometry data, such as Interferometric Synthetic Aperture Radar (InSAR), to measure co-seismic surface displacements and refine initial seismic estimates. GPS stations within the ANSS, for instance, provide real-time measurements of ground motion with millimeter accuracy, allowing for post-event adjustments to epicenter coordinates by modeling fault slip and deformation patterns. Satellite data from missions like Sentinel-1 further validate and correct locations, particularly for remote or offshore events where seismic coverage is sparse. These integrations have reduced uncertainties in complex tectonic settings.^[22]^[23] As of 2025, further innovations include crowdsourced detection using smartphone accelerometer networks, such as the Android Earthquake Alerts system, which leverages millions of devices worldwide to record seismic signals and contribute to real-time epicenter determination. This approach improves coverage in underserved regions and enables rapid location estimates by triangulating data from dense, opportunistic sensors, complementing traditional seismograph arrays.^[24] Accuracy of instrumental epicenter determinations varies by event magnitude, depth, and network density: global events monitored by the USGS typically achieve locations within 10-100 km horizontally, while local networks can refine positions to within 1-10 km or better for well-recorded shallow earthquakes. These levels reflect the propagation of uncertainties in velocity models and phase picking, with ongoing improvements from denser instrumentation and advanced computing.^[19]^[25]

Macroseismic Determination

Macroseismic determination involves locating the epicenter of an earthquake based on qualitative observations of its effects on the ground surface, structures, and human perceptions, rather than instrumental recordings. The macroseismic epicenter is defined as the surface location where the earthquake's intensity, assessed from reported damage and shaking, reaches its maximum value. This approach relies on compiling historical accounts, eyewitness reports, and damage assessments to map the distribution of shaking intensity, providing a practical method for pre-instrumental or sparsely instrumented events. In modern contexts, digital platforms like the USGS "Did You Feel It?" (DYFI) system collect crowd-sourced reports from internet users to generate real-time intensity maps, aiding in epicenter refinement for recent earthquakes by integrating felt data with instrumental locations.^[26]^[27] A primary method in macroseismic determination is the construction of isoseismal maps, which delineate contours of equal seismic intensity across affected areas. These maps are created by assigning intensity values to individual localities based on observed effects, such as structural damage or human sensations, and then interpolating contours to identify the intensity peak, which indicates the epicenter. Intensity assessments typically employ standardized scales like the Modified Mercalli Intensity (MMI) scale in the United States, which categorizes shaking from I (not felt) to XII (total destruction) using descriptors of damage to buildings and ground effects, or the European Macroseismic Scale (EMS-98) in Europe, which similarly grades intensities from I to XII but incorporates vulnerability classes for different building types to enhance objectivity. By fitting these data to attenuation models, the epicenter is refined as the point maximizing the observed intensity pattern.^[27]^[28]^[29] Historical examples illustrate the application of these techniques. For the 1755 Lisbon earthquake, the epicenter was estimated through analysis of damage reports from churches, public buildings, and residential structures across Portugal and Spain, with over 1,200 intensity data points compiled to map the maximum shaking near the Atlantic coast offshore Lisbon. This macroseismic approach revealed an epicentral intensity of around X-XI on the EMS-98 scale, highlighting severe destruction in stone masonry constructions as key indicators. Such methods were essential before modern seismographs, relying on archival records to reconstruct the event's location.^[30] Despite its utility, macroseismic determination has notable limitations due to its reliance on subjective human reports and uneven data distribution. Assessments can vary based on interpreters' judgments, leading to inconsistencies in intensity assignments and epicenter placement, as evidenced by surveys showing divergent results among seismologists applying the same rules to isoseismal data. Additionally, the method depends heavily on population density, with sparser reports in rural or offshore areas biasing locations toward populated regions and causing offsets from true instrumental epicenters of up to 50 km in some cases. These factors underscore the need for cautious integration with instrumental methods for greater precision.^[31]

Spatial and Measurement Concepts

Epicentral Distance

The epicentral distance is defined as the great-circle distance along the Earth's surface from the earthquake epicenter to a specific point of interest, such as a seismic station or affected location.^[32] This measure accounts for the planet's curvature, providing the shortest path over the spherical surface rather than a straight-line Euclidean distance through the Earth.^[33] In seismology, it is denoted by Δ and plays a key role in analyzing wave propagation and ground shaking effects.^[34] To calculate the epicentral distance, seismologists use the haversine formula, which computes the great-circle distance between two points given their latitudes (φ) and longitudes (λ). The formula is:

d = 2R \arcsin\left(\sqrt{\sin^2\left(\frac{\Delta\phi}{2}\right) + \cos\phi_1 \cos\phi_2 \sin^2\left(\frac{\Delta\lambda}{2}\right)}\right)

where R is the Earth's mean radius (approximately 6371 km), \Delta\phi = \phi_2 - \phi_1 and \Delta\lambda = \lambda_2 - \lambda_1 are the differences in latitude and longitude (in radians), and angles must be converted from degrees to radians for computation.^[35] This equation derives from spherical trigonometry, avoiding numerical instabilities near antipodal points by using half-angle identities.^[33] For an example, consider an epicenter at latitude φ₁ = 0° (equator) and longitude λ₁ = 0°, and a point at φ₂ = 0° and λ₂ = 1°. Converting to radians: Δφ = 0, Δλ ≈ 0.01745. Then,

a = \sin^2(0) + \cos(0) \cos(0) \sin^2(0.008726) \approx 7.615 \times 10^{-5},

c = 2 \arcsin(\sqrt{a}) \approx 0.01745 \text{ radians},

yielding d \approx 6371 \times 0.01745 \approx 111 km, consistent with the approximate 111 km per degree of latitude at the equator.^[33] This method is routinely applied in seismic data processing to determine distances from reported epicentral coordinates.^[35] Epicentral distance is integral to seismic intensity attenuation laws, which model how shaking intensity diminishes from the epicenter outward due to geometric spreading and material damping. Empirical models often express this as I = I_0 - k \log(d), where I is the intensity at distance d, I_0 is the epicentral intensity, and k is a region-specific coefficient (typically 1.5–3 for logarithmic decay). For instance, in the Iberian Peninsula, analyses of historical earthquakes yield forms incorporating logarithmic terms to fit observed data, aiding in probabilistic hazard assessments. These laws inform risk evaluation by predicting intensity contours and potential damage zones.^[36] In seismology reports, epicentral distances are typically reported in kilometers for practical applications, though angular degrees (Δ) are used for teleseismic studies where arc length is proportional via d = R \Delta (with Δ in radians).^[37] Miles may appear in some U.S.-centric summaries, but kilometers predominate in international standards.^[38]

Fault Rupture Dynamics

The epicenter serves as the surface projection of the hypocenter, marking the approximate point where seismic rupture initiates on the fault plane, though the precise initiation can vary along the fault due to local stress heterogeneities and nucleation processes. This initiation point represents the onset of dynamic slip, where accumulated tectonic strain is suddenly released, propagating as a fracture along the fault. In relation to the hypocenter discussed in basic definitions, the epicenter thus provides a surface reference for understanding the vertical and horizontal extent of rupture onset.^[39] Earthquake ruptures propagate either unilaterally, primarily in one direction from the initiation point, or bilaterally, extending in both directions, with unilateral propagation being more common in large events due to fault segmentation and stress barriers that arrest expansion in one direction. In unilateral ruptures, the epicenter is often positioned at or near one end of the fault segment, leading to asymmetric slip distribution and directivity effects that amplify ground motions in the propagation direction. For instance, the 2011 Tohoku-Oki earthquake (Mw 9.0) featured asymmetric bilateral rupture starting near the epicenter, initially propagating northward for about 50 seconds before shifting southwestward, resulting in a total rupture length of approximately 440 km along the subduction interface.^[40] Rupture velocity, typically ranging from 2 to 3 km/s in crustal and subduction zone earthquakes, governs the speed at which the slip front advances along the fault, often subsonic relative to shear wave speeds to maintain stability. This velocity, combined with fault dimensions—such as lengths of tens to hundreds of kilometers and widths of 50 to 200 km—allows the rupture zone to extend far beyond the epicenter, encompassing multiple asperities where peak slip occurs. Bilateral ruptures tend to have the epicenter near the midpoint, balancing propagation, while unilateral cases shift it toward the up-dip or along-strike edge, influencing the overall energy release pattern.^[41]^[40] Advancements in the 2020s have utilized finite-fault inversions integrating Interferometric Synthetic Aperture Radar (InSAR) data with seismic waveforms to map epicenter-rupture relationships with high precision, revealing nuances in initiation points and propagation paths not captured by early models. These methods constrain rupture kinematics by jointly inverting surface deformation and body waves, often identifying the epicenter as offset from the centroid of slip in complex fault systems. For example, in the 2022 Mw 6.7 Menyuan earthquake, such inversions delineated a multi-segment bilateral rupture extending approximately 24 km along a left-lateral strike-slip fault, with the epicenter located near the center of the rupture zone. Similarly, analyses of the 2023 Mw 7.8 Türkiye earthquake highlighted geometry-driven phases of rupture acceleration, where InSAR-constrained models showed the epicenter near a fault bend influencing bilateral-to-unilateral transitions.^[42]^[43]^[44]

Effects and Applications

Surface Damage Patterns

Surface damage from earthquakes typically exhibits the highest severity near the epicenter, where ground shaking is most intense, and decreases with increasing epicentral distance due to the attenuation of seismic waves. This radial pattern is observed in intensity measures, such as the Modified Mercalli Intensity scale, which quantifies damage based on observed effects like structural collapses and ground failures. However, the decrease is not uniform, as local geology can lead to anisotropic damage distribution, with amplification in areas of soft sediments or basins that resonate with seismic frequencies.^[45]^[5]^[46] Key factors influencing these patterns include site effects, where unconsolidated soils amplify shaking more than firm bedrock, and rupture directivity, which directs stronger pulses of energy toward specific azimuths along the fault propagation direction. Directivity effects can result in forward-rupture zones experiencing up to twice the peak ground velocity compared to other directions, exacerbating damage asymmetry. These variations underscore why damage maps often show irregular contours rather than perfect circles centered on the epicenter.^[47]^[48] In the 1989 Loma Prieta earthquake (M6.9), damage correlated with epicentral distance but was markedly influenced by site conditions; while the epicenter in the Santa Cruz Mountains saw limited structural failure in engineered buildings, areas like the Marina District in San Francisco—about 100 km away—experienced severe collapses due to soil liquefaction and amplification on reclaimed bay mud. Similarly, the 2023 Kahramanmaraş earthquake sequence (M7.8 and M7.5) revealed extensive near-epicenter liquefaction in regions like Iskenderun and Golbasi, where saturated sands failed under intense shaking, contributing to widespread building collapses despite existing codes; post-event analyses highlighted how lax enforcement amplified damage in proximity to the fault, with over 50,000 fatalities linked to these failures. These cases illustrate how geological heterogeneity and construction practices can override simple distance-based expectations in damage patterns.^[49]^[50]^[51]^[52] More recently, the March 28, 2025, M7.7 Myanmar earthquake near Mandalay demonstrated similar deviations, with most devastation and over 3,600 fatalities concentrated within 15 km of the epicenter along the Sagaing Fault, but notable structural damage reported in Bangkok, Thailand—approximately 1,000 km away—due to amplification in the sedimentary basin.^[53]

Practical Uses in Seismology

The Pacific Tsunami Warning Center (PTWC) relies on the epicenter location of an earthquake as a key factor in issuing tsunami warnings and advisories. If the epicenter is near coastal areas, the PTWC issues local warnings to nearby regions based on seismic data indicating potential tsunami generation. For epicenters in the open ocean, regional or ocean-wide advisories are triggered to alert distant coasts, with travel time maps calculated from the epicenter to predict wave arrival.^[54] Epicenter data from historical earthquake catalogs contributes to probabilistic seismic hazard models, such as the USGS National Seismic Hazard Maps, by informing distributed seismicity rates and fault source characterizations. These catalogs, which include precise epicentral locations, enable the estimation of ground-shaking probabilities across regions, supporting zoning for building codes and risk assessment. The 2023 update of the National Seismic Hazard Model incorporates refined catalog data to enhance accuracy in hazard delineation.^[55]^[56] In emergency response, rapid epicenter determination facilitates public alerts through applications like MyShake, which delivers ShakeAlert notifications including the earthquake's location to users in affected areas. This enables timely evacuation decisions, with alerts providing seconds of warning based on the epicenter's distance from population centers in California, Oregon, and Washington. MyShake's integration with ShakeAlert has been evaluated for user experience in promoting safety actions during events.^[57]^[58] Epicenters of past earthquakes are essential in seismological research for analyzing fault segmentation and recurrence patterns, particularly along the San Andreas Fault system. By mapping epicentral distributions, researchers identify fault segments, such as the four major divisions in the northern San Andreas used in probability models for the San Francisco Bay Region. This approach supports estimates of recurrence intervals, as seen in studies of quasi-periodic events at Parkfield, aiding long-term forecasting.^[59]^[60]

History and Terminology

Etymology

The term "epicenter" derives from the Ancient Greek prefix epi- (ἐπί), meaning "upon" or "above," combined with kentron (κέντρον), meaning "center" or "point," to denote a position situated over or atop a central point. This etymological construction entered scientific vocabulary through Modern Latin epicentrum, reflecting its literal sense of "upon the center."^[61] In seismology, the word was first employed by Irish civil engineer and geologist Robert Mallet in his seminal 1846 paper "On the Dynamics of Earthquakes," presented to the Royal Irish Academy, where he described it as the surface point vertically above the underground origin—or focus—of seismic activity. Mallet's usage marked a precise terminological innovation, evolving from vaguer 19th-century expressions like "center of disturbance" in geological literature, and helped formalize the study of earthquakes as a distinct scientific discipline.^[62]^[63] The term gained wider adoption in the late 19th century, appearing in U.S. Geological Survey reports, such as Clarence E. Dutton's 1889 analysis of the Charleston earthquake, which referenced multiple surface points of maximum intensity as "epicenters." Spelling conventions vary by region: "epicenter" predominates in American English, while "epicentre" is standard in British English. Pronunciation follows a similar pattern, with American English rendering it as /ˈɛpɪˌsɛntɚ/ and British as /ˈɛpɪsɛntə/. Beyond seismology, "epicenter" has entered general English as a metaphor for the focal or most intense point of non-physical phenomena, such as the "epicenter of innovation" in a city or the "epicenter of a controversy," emphasizing concentrated impact rather than literal positioning. However, this extended usage stems directly from its seismic origins and remains secondary to its technical definition in geophysics.^[64]

Historical Evolution

The concept of the epicenter emerged gradually from ancient philosophical explanations of earthquakes, which lacked any notion of a precise surface projection of the subsurface rupture. In ancient Greece, Aristotle (c. 384–322 BCE) proposed that earthquakes resulted from subterranean winds trapped in caverns and released explosively, viewing them as diffuse atmospheric or geological events rather than localized phenomena with a definable origin point. This perspective, detailed in his Meteorologica, emphasized causes over spatial mapping and influenced Western thought for centuries without developing tools for pinpointing an epicenter.^[65]^[66] The 19th century marked the transition to empirical methods for locating earthquake "centers," pioneered by Irish civil engineer Robert Mallet. Mallet first used the term "epicentre" in his 1846 paper and applied it in his 1862 report on the 1857 Basilicata earthquake in southern Italy, where he analyzed damage patterns—including the orientation of wall cracks, fallen masonry alignments, and structural displacements—to infer the direction and approximate position of the seismic origin. His fieldwork, supported by the Royal Society, demonstrated that radial patterns in destruction could reveal the epicenter's location and even estimate focal depth, laying foundational principles for macroseismic analysis. Complementing this, Mallet's artificial earthquake experiments from 1847 to 1858 used controlled explosions to measure seismic wave velocities in various media, providing early insights into wave propagation from a source point.^[67]^[68]^[69]^[70] The 20th century shifted toward instrumental precision, with the epicenter becoming integral to quantitative seismology. In 1935, Charles F. Richter developed the local magnitude scale (M_L) at the California Institute of Technology, which calculated earthquake strength based on the logarithm of maximum seismic wave amplitude recorded on Wood-Anderson seismographs, adjusted for distance from the epicenter; this required accurate hypocentral locations to calibrate magnitudes for southern California events. The scale's adoption worldwide standardized epicenter usage in magnitude assessments. By the 1960s, the U.S. Coast and Geodetic Survey's Worldwide Standardized Seismograph Network (WWSSN), comprising over 120 stations, revolutionized global epicenter determination by enabling precise triangulation of P- and S-wave arrival times, reducing location uncertainties from hundreds to tens of kilometers and supporting plate tectonics research.^[71]^[72]^[73] In the 21st century, computational and network advancements have refined epicenter estimation for real-time applications, spurred by events like the 2010 M_w 7.0 Haiti earthquake, which exposed gaps in rapid location for vulnerable regions. Post-Haiti, the USGS expanded near-real-time processing, integrating dense seismic arrays and GPS data to compute epicenters within 10–60 seconds using algorithms like HypoInverse for initial locations and finite-fault inversions for refinements. Machine learning models, such as deep neural networks for phase picking (e.g., PhaseNet, 2019), have accelerated detection by automating waveform analysis, achieving sub-minute epicenter alerts in systems like ShakeAlert, which now covers the U.S. West Coast and informs global early warning efforts. These developments prioritize speed and accuracy, with post-2010 investments in Caribbean monitoring networks enhancing epicenter reliability for disaster response.^[74]^[75]^[76]

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Rupture process of the 2011 Tohoku‐oki earthquake and absolute ...
Oct 13, 2011 · The estimated seismic moment is 5.7 × 1022 Nm (Mw = 9.1), associated with a fault rupture 440 km long and 180 km wide along the plate interface.
[39]
Global catalog of earthquake rupture velocities shows ...
May 9, 2018 · Average rupture velocities slower than 3100 m/s represent 75% of the catalog. Several undocumented fast ruptures, very likely supershear, are ...
[40]
Rupture process of the January 8, 2022, Menyuan M 6.9 earthquake
In this study, InSAR coseismic deformation data and far-field waveform data were used to jointly invert the earthquake rupture process, and a four-segment ...
[41]
Rupture phases reveal geometry-related rupture propagation in a ...
Jan 22, 2025 · Some studies used the velocity peaks or energy envelopes to derive an average propagation speed of 2.8 to 3.2 km/s (26, 27, 31).
[42]
Rupture phases reveal geometry-related rupture propagation in a ...
Jan 22, 2025 · Rupture phases observed in the 2023 M w 7.8 Türkiye earthquake reveal complex earthquake rupture related to fault geometry.
[43]
Earthquake Magnitude, Energy Release, and Shaking Intensity
Magnitude is the size of the earthquake, energy release is the potential for damage, and intensity is the measure of shaking at each location.View Media Details · Magnitude Types · How much bigger is a...
[44]
Effects of Earthquakes - CSULB
Earthquakes cause many different kinds of damage depending on the strength of the quake, distance, type of underlying rock or soil and the building ...
[45]
What is Directivity? - Earthquake Hazards Program
Earthquake directivity is the focusing of wave energy along the fault in the direction of rupture. This means that, exclusive of local site conditions such as ...
[46]
Directivity - an overview | ScienceDirect Topics
Directivity is the effect on the seismograms of rupture propagation along the fault. It impacts both the high-frequency and the low-frequency seismograms.
[47]
The Loma Prieta, California, Earthquake of October 17, 1989
Jul 13, 2006 · Damage to vulnerable structures from the earthquake varied substantially with the distance from the causative fault and the type of underlying ...Missing: epicentral | Show results with:epicentral
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M 6.9 October 17, 1989 Loma Prieta Earthquake - USGS.gov
Oct 17, 1989 · Engineered buildings, including those near the epicenter, performed well during the earthquake. Most of the severe damage was sustained by ...
[49]
Geotechnical damage survey report on February 6, 2023 Turkey ...
The survey found landslides in Islahiye and Tepehan, liquefaction in Iskenderun and Golbasi, and building damage in Antakya and Kahramanmaras.
[50]
Soil liquefaction sites following the February 6, 2023 ...
Mar 18, 2024 · On February 6, 2023, two earthquakes, with moment magnitudes M7.8 and M7.6, occurred in Kahramanmaraş-Türkiye on the East Anatolian Fault zone, ...
[51]
[PDF] Operational users guide for the Pacific Tsunami Warning and ...
On the basis of this seismic evidence, the Center issues a local tsunami warning or advisory to areas located near the epicenter. A regional (sometimes ocean- ...
[52]
Earthquake Catalogs for the USGS National Seismic Hazard Maps
Oct 24, 2018 · We describe a methodology that has been developed at the US Geological Survey for making earthquake catalogs for seismic hazard analysis.
[53]
National Seismic Hazard Model | U.S. Geological Survey - USGS.gov
The USGS maps are the basis for seismic provisions in building codes and for risk models used in insurance rate structures. An integral part of this project is ...
[54]
User Experience of Early Warning Delivery and Earthquake Shaking
Aug 5, 2022 · MyShake is a free citizen science and public safety smartphone application that delivers the United States ShakeAlert program's Earthquake Early Warning to the ...
[55]
MyShake app
MyShake app provides earthquake alerts, damage reports, and helps build a global seismic network, delivering ShakeAlert alerts in CA, OR, and WA.
[56]
Earthquake Probabilities in the San Francisco Bay Region: 2000 to ...
Dec 7, 2016 · WG99 has built upon the WGNCEP segmentation model and divides the northern San Andreas Fault into four major segments. From north to south ...
[57]
[PDF] 02HQGR0061 Paul Segall Testing Earthquake Recurrence Models ...
San Andreas fault in central California we estimated rigorous bounds on the recurrence time ... Andreas is the 1966 epicenter, asterisk is the town of Parkfield.
[58]
Epicenter - Etymology, Origin & Meaning
1885 in seismology, "point on the earth's surface directly above the center or focus of an earthquake," from Modern Latin epicentrum (1879 in geological use).Missing: coined | Show results with:coined
[59]
https://pubs.usgs.gov/of/1999/0517/intro.html
[60]
Scientist of the Day - Robert Mallet, Irish Engineer and Geologist
Jun 3, 2021 · It occurred on Dec. 16, 1857, with an epicenter near Montemurro, and it was the most devastating seismic event of the century. About 10,000 ...
[61]
What is the Epicenter? | Meaning Breakdown - Merriam-Webster
Deriving from Greek by way of Latin, the prefix epi- means “upon” or “over,” among other things. So it makes sense that the epicenter sits above the site where ...
[62]
Aristotle and Earthquake Data: A Historical Note - ResearchGate
Aug 6, 2025 · The earliest known written work on earthquake theory was written by Aristotle (c. 330 BC). Aristotle had collected a lot of earthquake data.
[63]
[PDF] Historical Earthquake Theories Historische Erdbebentheorien ...
ARISTOTLE was the first to deliver a rational theory of earthquakes. In contradistinction to mythical and astrological theories. (conjunction of planets, comets) ...
[64]
Mallet, Robert - Dictionary of Irish Biography
He invented and patented buckled plates (1852), which combined maximum strength with minimum depth and weight and were used to floor the Westminster and London ...Missing: epicenter | Show results with:epicenter<|control11|><|separator|>
[65]
Robert Mallet - Oxford Reference
In a series of experiments starting in 1850, Mallet attempted to determine the speed of earthquake waves. He did this by setting off small explosives at ...
[66]
Robert Mallet Founds the Science of Seismology
Robert Mallet founded seismology, coined the term, created terms like "epicenter", and determined seismic wave speeds in different materials.
[67]
Richter scale | Seismology, Earthquake Magnitude & Intensity
Oct 27, 2025 · The scale was developed for temblors occuring in southern California that were recorded using the Wood-Anderson seismograph and whose epicentres ...
[68]
[PDF] The Richter scale: its development and use for determining ...
The M, scale, introduced by Richter in 1935, is the antecedent of every magnitude scale in use today. The scale is defined such that a magnitude-3.
[69]
Achievements and Prospects of Global Broadband Seismographic ...
Jul 19, 2022 · Deployment of the WWSSN in the early 1960s (Figure 1) substantially improved global seismic station coverage and enhanced monitoring ...
[70]
USGS Near‐Real‐Time Products—and Their Use—for the 2018 ...
Dec 11, 2019 · The most fundamental near‐real‐time information that the USGS produces is the identification and description of the earthquake itself, which ...<|control11|><|separator|>
[71]
Real‐Time Earthquake Detection and Magnitude Estimation Using ...
Apr 14, 2022 · An integrated deep learning framework for real-time earthquake detection and magnitude estimation is developed The new framework leverages ...
[72]
Earthquake Early Warning: Advances, Scientific Challenges, and ...
Earthquake early warning (EEW) is the rapid detection and characterization of earthquakes and delivery of an alert so that protective actions can be taken.