Earthquake Report: M 7.7 Burma

Two nights ago as I was falling asleep there was a magnitude M 7.7 earthquake in Burma.

https://earthquake.usgs.gov/earthquakes/eventpage/us7000pn9s/executive

Upon viewing the earthquake location on the map (the epicenter), I knew this was associated with the Sagaing fault. We will learn more about this fault system as we journey through this Earthquake Report.

I had been preparing a report for the M 6.7 earthquake along the Puysegur convergent plate margin in southwest New Zealand. I will get back to that report later as it was an interesting earthquake.

This region of Burma (Myanmar) is amidst the fourth year of a civil war and the government has continued to launch attacks in the epicentral region (Sagaing, Mandalay, etc.). Their emergency response efforts were focused in the region to the south (for political reasons) and they were not sending aid into Sagaing/Mandalay.

Though, the govt is now letting China and India to bring aid into these more heavily hit areas.

The USGS PAGER alert program (funded by USAID) uses a combination of population density and earthquake ground shaking data to estimate the likelihood of the number of fatalities and the amount of economic impact to physical infrastructure.

Shortly after the temblor, the PAGER alert for this earthquake showed a high probability for large numbers of fatalities and significant economic impact.

The USGS earthquake program produces a suite of products for earthquakes downloadable from the earthquake event page.

These USGS products are initially generated automatically but are updated over time. For large and interesting earthquakes, these products may have many updates. At the time I write this, the USGS version number is 12.

Below is the 12th version of the PAGER estimates for this earthquake.



The USGS also use statistics from previous earthquakes (empirical relations between earthquake fault parameters and earthquake magnitude) to drive a computer model that generates an aftershock forecast.

Every fault has a unique parameters (e.g., the “b-value”) and this parameter can change with time. So these aftershock forecasts are heavily dependent upon the parameters the USGS chooses for each forecast. They are pretty good at this.

Here is the aftershock forecast at the time that I write this (3/30 19:00 pacific time). The length of each colored bar stands for the chance of an earthquake for a given magnitude over the next week.


Below i present some information about this earthquake and the tectonics of the area and region. We must always be clear that this information is important to help people prepare their surroundings for earthquakes (e.g., through the successful application of building codes).

However, this is not always the case.

  • Sometimes the building code is not strong enough.
  • Sometimes the building code is not followed for some reason.
  • Sometimes the earthquake is larger in size than the building code was designed to meet.

We must have empathy for those suffering from these natural hazards. Hopefully we will continue to reduce the impact of these natural hazards, so that we can all see less suffering in the world.

Tectonic Setting.

    This part of the world is dominated by the alpide belt, one of the largest convergent plate boundaries on earth.

    The Alpide Belt begins along the collision zone between Australia on the south and Java (and other islands east of Java) on the north. This turns into a subduction zone as the fault extends to the west and northwest (e.g., Sumata), where the 2004 Boxing Day Earthquake happened.

    Depending upon the orientation of the plate boundary, the fault system changes from pure convergence (pure subduction or pure collision) to oblique convergence.

    In Sumatra, the convergence is oblique. Since the fault is not perpendicular to the convergence, the relative plate motion is not purely convergent (i.e., pure thrust faults). Strike-slip faults form to accommodate this lateral relative motion.

    This type of strike-slip fault is called a forearc sliver fault. There are other examples of these “strain partitioning” (where the tectonic strain is “partitioned” between thrust faults and strike-slip faults).

    This forearc sliver fault (the Sumatra fault) extends northwards from southern Sumatra, into the Andaman Sea (where there is some backarc spreading) and onshore to form the Sagaing fault.

    The subduction zone follows along with and eventually turns into the collision zone that forms the Himalayas, the Zagros fold and thrust belt, the collision zone that forms the Alps, and terminates somewhere west of Portugal.

    The Sagaing fault is a right-lateral strike-slip fault with a slip rate between 15 and 25 millimeters per year (similar rate as the San Andreas fault system in California, USA).

    In 2018 Ray Weldon and others ran a paleoseismology (the study of prehistoric earthquakes) field workshop in Burma. They studies a portion of the faults in this region.

    Based on studies of prehistoric and historic earthquakes along the Sagaing fault, the section of the fault (the Meiktila section) that slipped during this M 7.7 earthquake had not had an earthquake since 1839.

    A geologist had even suggested that when this part of the fault slips next, it would be a M 7.7 earthquake!

    The India plate is moving northwards, pummeling into the southern part of the Eurasia plate, at a rate of about 25 to 50 mm per year, depending upon the reference frame (Pusok and Stegman, 2020). The India plate began moving northward from Antarctica since before 80 million years ago.

    The details of the story has changed as more geological information is interpreted. But the general story is that the India plate moved away from Antarctica as an oceanic spreading center formed between these plates. The India plate moved towards Asia.

    Prior to about 45-50 Ma, there was oceanic crust between India and Eurasia. But at this time, the continental crust of the India and Eurasia plates collided. This collision would eventually cause uplift of the Himalaya mountain range and the Tibetan Plateau to the north of the Himalaya.

    There are marine fossils on the top of the mountains in the Himalaya! (this is how we know there was ocean between these plates in the past)

    Here is a time series showing the convergence of these two plates modified from Pusok & Stegman (2020) and the USGS.


    A part of the tectonic story is told by one of the rock stars of plate tectonics, Dr. Paul Tapponier. Tapponier conducted experiments that showed how north-south convergence, like that of India and Asia, coupled with a backstop (something that is more difficult to move) from the west, would lead to some crust to squish out to the east.

    This is called extrusion tectonics as the crust of eastern Asia is being extruded to the east, like a watermelon seed is extruded from between one’s fingers when they squeeze on the wet seed.

    Below is a color version of the results from Tapponier’s experiment. Compare this with maps showing the GPS motion of the crust in this region.


    Note that the plastic has numerous faults develop as part of the extrusion. We can see how the blue and yellow lines show lateral offset along these faults.

    Many of these faults are left-lateral strike-slip faults. Strike-slip means that the curst moves side-by-side when looking down on the crust from outer space (or an airplane, or Google Earth).

    Left-lateral means that, when standing on one side of the fault, looking across the fault at something, that thin one is looking at is moving to the left during an earthquake. More about tectonic fundamentals here.

    In the map on the right ^^^ we can see that these left-lateral strike-slip faults that are mapped in the region are just like the faults in the blue-yellow plastic.

    One of the major left-lateral strike-slip faults along the Tibetan Plateau is the Kunlun fault, which has been well studied in places. A tectonic history of the region, and how the Kunlun fault fits into this history, is presented by Staisch et al., 2020.

    There are also right-lateral strike-slip faults. Note the red arrow to the east of India, showing that the crust west of a fault is moving northwards. This is the Sagaing fault, where the M 7.7 earthquake ruptured the Earth’s surface.

Below is my interpretive poster for this earthquake

  • I plot the seismicity from the past month, with diameter representing magnitude (see legend). I include earthquake epicenters from 1925-2025 with magnitudes M ≥ 3.0 in one version.
  • I plot the USGS fault plane solutions (moment tensors in blue and focal mechanisms in orange), possibly in addition to some relevant historic earthquakes.
  • A review of the basic base map variations and data that I use for the interpretive posters can be found on the Earthquake Reports page. I have improved these posters over time and some of this background information applies to the older posters.
  • Some basic fundamentals of earthquake geology and plate tectonics can be found on the Earthquake Plate Tectonic Fundamentals page.

    I include some inset figures. Some of the same figures are located in different places on the larger scale map below.

  • In the upper left corner is a map showing the plate tectonic boundaries (from the GEM).
  • In the lower right corner is a map that shows the M 7.7 earthquake intensity using the modified Mercalli intensity scale. Earthquake intensity is a measure of how strongly the Earth shakes during an earthquake, so gets smaller the further away one is from the earthquake epicenter. The map colors represent a model of what the intensity may be. The USGS has a system called “Did You Feel It?” (DYFI) where people enter their observations from the earthquake and the USGS calculates what the intensity was for that person. The dots with yellow labels show what people actually felt in those different locations.
  • To the left of the intensity map is a plot that shows the same intensity (both modeled and reported) data as displayed on the map. Note how the intensity gets smaller with distance from the earthquake.
  • Above the intensity plot are two profiles that show estimates of the slip rate along the Sagaing fault. The plot on the left shows a 22.4 mm/yr slip rate and the plot on the right shows a 17 mm/yr slip rate.
  • In the upper right corner are two maps showing the possibility of earthquake induced liquefaction for these two earthquakes. I discuss these phenomena in more detail later in the report.
  • To the left of these ground failure maps is a map showing the earthquake history for the region.
  • To the right of the tectonic boundary map is another map showing earthquake faults that are part of the Sagaing fault system, with a space time diagram showing these earthquakes back through time.
  • In the middle left is the USGS finite fault model for the M 7.7 earthquake. They model slip on a rectangular fault and color represents how much the fault moved (up to about 6.5 meters).
  • In the lower left is a plot from Wells and Coppersmith (1994) showing the empirical relations between subsurface fault rupture length and earthquake magnitude. The USGS fault model is 350 km long, but this corresponds to a M 8.2 earthquake. Something does not match.
  • Here is the map with a week’s seismicity plotted.


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Other Report Pages

Shaking Intensity

  • Here is a figure that shows a more detailed comparison between the modeled intensity and the reported intensity. Both data use the same color scale, the Modified Mercalli Intensity Scale (MMI). More about this can be found here. The colors and contours on the map are results from the USGS modeled intensity. The DYFI data are plotted as colored dots (color = MMI, diameter = number of reports).
  • In the upper panel is the USGS Did You Feel It reports map, showing reports as colored dots using the MMI color scale. Underlain on this map are colored areas showing the USGS modeled estimate for shaking intensity (MMI scale).
  • In the lower panel is a plot showing MMI intensity (vertical axis) relative to distance from the earthquake (horizontal axis). The models are represented by the green and orange lines. The DYFI data are plotted as light blue dots. The mean and median (different types of “average”) are plotted as orange and purple dots. Note how well the reports fit the green line (the model that represents how MMI works based on quakes in California).
  • Below the map and the lower plot is the USGS MMI Intensity scale, which lists the level of damage for each level of intensity, along with approximate measures of how strongly the ground shakes at these intensities, showing levels in acceleration (Peak Ground Acceleration, PGA) and velocity (Peak Ground Velocity, PGV).


Potential for Ground Failure

  • Below are a series of maps that show the potential for landslides and liquefaction. These are all USGS data products.
    There are many different ways in which a landslide can be triggered. The first order relations behind slope failure (landslides) is that the “resisting” forces that are preventing slope failure (e.g. the strength of the bedrock or soil) are overcome by the “driving” forces that are pushing this land downwards (e.g. gravity). The ratio of resisting forces to driving forces is called the Factor of Safety (FOS). We can write this ratio like this:

    FOS = Resisting Force / Driving Force

  • When FOS > 1, the slope is stable and when FOS < 1, the slope fails and we get a landslide. The illustration below shows these relations. Note how the slope angle α can take part in this ratio (the steeper the slope, the greater impact of the mass of the slope can contribute to driving forces). The real world is more complicated than the simplified illustration below.


  • Landslide ground shaking can change the Factor of Safety in several ways that might increase the driving force or decrease the resisting force. Keefer (1984) studied a global data set of earthquake triggered landslides and found that larger earthquakes trigger larger and more numerous landslides across a larger area than do smaller earthquakes. Earthquakes can cause landslides because the seismic waves can cause the driving force to increase (the earthquake motions can “push” the land downwards), leading to a landslide. In addition, ground shaking can change the strength of these earth materials (a form of resisting force) with a process called liquefaction.
  • Sediment or soil strength is based upon the ability for sediment particles to push against each other without moving. This is a combination of friction and the forces exerted between these particles. This is loosely what we call the “angle of internal friction.” Liquefaction is a process by which pore pressure increases cause water to push out against the sediment particles so that they are no longer touching.
  • An analogy that some may be familiar with relates to a visit to the beach. When one is walking on the wet sand near the shoreline, the sand may hold the weight of our body generally pretty well. However, if we stop and vibrate our feet back and forth, this causes pore pressure to increase and we sink into the sand as the sand liquefies. Or, at least our feet sink into the sand.
  • Below is a diagram showing how an increase in pore pressure can push against the sediment particles so that they are not touching any more. This allows the particles to move around and this is why our feet sink in the sand in the analogy above. This is also what changes the strength of earth materials such that a landslide can be triggered.


  • Here Dr. Bohon demonstrates the phenomena of liquefaction.
    • @drwendyrocksit #Liquefaction is a process by which water-saturated sediment temporarily loses strength and acts as a fluid. This can happen during #earthquake shaking. #geophysics #geology ♬ Quicksand – Hatchie

  • And, another video demonstration.

  • Below is a diagram based upon a publication designed to educate the public about landslides and the processes that trigger them (USGS, 2004). Additional background information about landslide types can be found in Highland et al. (2008). There was a variety of landslide types that can be observed surrounding the earthquake region. So, this illustration can help people when they observing the landscape response to the earthquake whether they are using aerial imagery, photos in newspaper or website articles, or videos on social media. Will you be able to locate a landslide scarp or the toe of a landslide? This figure shows a rotational landslide, one where the land rotates along a curvilinear failure surface.


  • Below is the liquefaction susceptibility and landslide probability map (Jessee et al., 2017; Zhu et al., 2017). Please head over to that report for more information about the USGS Ground Failure products (landslides and liquefaction). Basically, earthquakes shake the ground and this ground shaking can cause landslides.
  • I use the same color scheme that the USGS uses on their website. Note how the areas that are more likely to have experienced earthquake induced liquefaction are in the valleys. Learn more about how the USGS prepares these model results here.


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    Some Relevant Discussion and Figures

    • This is a tectonic map from Molnar and Tapponier (1975).
    • “We stand on the shoulders of giants.”


      • Preliminary map of recent tectonics in Asia. Bold lines represent faults of major importance-usually seismic and with very sharp morphology. Bold arrows indicate sense of motion, corroborated by fault plane solutions or surface faulting of earthquakes (6. 30. 33, 34). Open arrows indicate sense inferred from analysis of photographs. For Tertiary folding bold symbols indicate more prominent, more recent folds. The dotted areas indicate region of inferred recent vertical motion associated with thrust faulting and compressional tectonics. Areas shaded by dashed lines are covered by thick recent alluvial deposits and are dominated by horizontal extension and subsidence (/4). Contours in the northeast China basins and recent volcanic centers. except for the Hsing An fissure basalts, are from Terman (43). This map is preliminary; coverage by ERTS photographs is not complete, and surely many features relevant to the understanding of Asian tectonics have not yet been recognized or were not plotted. The names of faults are not official names but purely for reference in this article.

    • This is a later map from Tapponier et al. (1982) as part of his paper on extrusion tectonics.


      • Schematic map of Cenozoic extrusion tectonics and large faults in eastern Asia. Heavy lines = major faults or plate boundaries; thin lines = less important faults. Open barbs indicate subduction; solid barbs indicate intracontinental thrusts. White arrows represent qualitatively major block motions with respect to Siberia (rotations are not represented). Black arrows indicate direction of extrusion-related extension. Numbers refer to extrusion phases: 1 =50 to 20 m.y. B.P.; 2 = 20 to 0 m.y. B.P.; 3 = most recent and future. Arrows on faults in western Malaysia, Gulf of Thailand, and southwestern China Sea (earliest extrusion phase) do not correspond to present-day motions.

    • Here is the Curray (2005) plate tectonic map.


      • Tectonic map of part of the northeastern Indian Ocean. Modified from Curray (1991).

    • Here is a map from Maurin and Rangin (2009) that shows the regional tectonics at a larger scale. They show how the Burma and Sunda plates are configured, along with the major plate boundary faults and tectonic features (ninetyeast ridge). The plate motion vectors for India vs Sunda (I/S) and India vs Burma (I/B) are shown in the middle of the map. Note the Sunda trench is a subduction zone, and the IBW is also a zone of convergence. There is still some debate about the sense of motion of the plate boundary between these two systems. This map shows it as strike slip, though there is evidence that this region slipped as a subduction zone (not strike-slip) during the 2004 Sumatra-Andaman subduction zone earthquake. I include their figure caption as a blockquote below.


      • Structural fabric of the Bay of Bengal with its present kinematic setting. Shaded background is the gravity map from Sandwell and Smith [1997]. Fractures and magnetic anomalies in black color are from Desa et al.[2006]. Dashed black lines are inferred oceanic fracture zones which directions are deduced from Desa et al. in the Bay of Bengal and from the gravity map east of the 90E Ridge. We have flagged particularly the 90E and the 85E ridges (thick black lines). Gray arrow shows the Indo-Burmese Wedge (indicated as a white and blue hatched area) growth direction discussed in this paper. For kinematics, black arrows show the motion of the India Plate with respect to the Burma Plate and to the Sunda Plate (I/B and I/S, respectively). The Eurasia, Burma, and Sunda plates are represented in green, blue, and red, respectively.

    • Here are some figures from Fadil et al. (2023). Fadil et al. (2023) used a high resolution focal mechanism catalog to evaluate the seismogenic depth for faults in Burma.
    • Focal mechanisms tell us about the orientation of the faults that slip during earthquakes.
    • Seismogenic depth refers to the depth that faults are capable of producing earthquakes.
    • This first map shows the earthquakes that they used, as well as some cross sections of the seismicity. Cross section P2 crosses the Sagaing fault where the 28 March 2025 M 7.7 earthquake epicenter is located.


      • (a) Historical earthquakes in Myanmar and surrounding regions from global earthquake catalogs. The circles represent hypocenters from Global Historical Earthquake Archive (GHEA; 1664–1956; Albini et al., 2014) and International Seismological Center (ISC) earthquake catalogs (1964–2021). The focal mechanism represent focal mechanisms from Global Centroid Moment Tensor (Global CMT) catalog (1976–2021) plotted at their centroid locations. M >7 earthquakes are labelled by year, mag. The black lines represent mapped geological faults from Wang et al. (2014). The black vectors represent the motion of India relative to the Shan–Thai block (Mallick et al., 2019). (b–d) Elevation (SRTM90m; Jarvis et al., 2008) and depth cross sections along three trench perpendicular profiles (P1–P3) indicated in panel (a). Earthquakes within 25 km of the profile are projected onto the cross section. Colored contours indicate the estimated depth to the top of the Indian plate from slab2 (Hayes et al., 2018). (e) Elevation and depth cross section along the Sagaing fault (profile P4). Abbreviations: CMB, central Myanmar basin; EHS, eastern Himalayan syntaxis; IMR, Indo-Myanmar range; MDY, Mandalay; MFT, main frontal thrust; NPT, Nay Pyi Taw;SF, Sagaing fault; and YGN, Yangon. ? means that the earthquake magnitude is unknown and inferred from historical documents.

    • This map shows the focal mechanisms for the earthquakes used in their study.
    • On the left are earthquakes located withing the overriding plates. On the right are earthquakes that are within the India plate.


      • Focal mechanisms of earthquakes in this study (a) within the overriding Myanmar plate and Shan–Thai block (centroid depth >40 km) and (b) within the subducting Indian plate (centroid depth >40 km). The black dashed boxes indicate thrust earthquakes close to the Sagaing fault. The black solid box indicates earthquakes at lower crust to uppermost mantle depths. Focal mechanisms of earthquakes within the Indian plate (centroid depth >40 km). Note the different depth color scales in each panel. Tectonic faults are plotted as black lines (Wang et al., 2014), and red triangles indicate locations of volcanoes and lava fields. The black arrows show the motion of India relative to the Shan–Thai block in mm/yr (Mallick et al., 2019). The red contours indicate depth to the top of Indian slab estimated from slab2. Cross section profiles (A–A′ to H–H′) are shown in Figure 8. ADB, Ayeyarwaddy delta basin; BYB, Bago Yoma basin; BYR, Bago Yoma range; CMf, Churachandpur Mao fault; Kyf, Kyaukkyan fault; MPf, Mae Ping fault; Nf, Nanting fault; PB, Pyay basin; SB, Shwebo basin; and WPA, Wuntho-Popa arc.

    • These are the cross sections with the mechanisms plotted.
    • Note that these mechanisms are drawn as if one was looking at them from the side, not the top as we usually view them.


      • Cross sections perpendicular to the subduction front from north to south along profiles in Figure 7b, showing the location of relocated focal mechanisms and seismicity beneath the Indo-Myanmar range (IMR) and central Myanmar basin (CMB). The focal mechanism plots colored by depth represent earthquakes in this study, while gray focal mechanisms represent Global CMT mechanisms plotted at centroid depth (1976–2021). The circles represent relocated seismicity from ISC-Engdahl–van der Hilst–Buland catalog (EHB) catalog (gray), HYPODD relocations from Mon et al. (2020) (magenta), and tomoDD relocations from Zhang, He, et al. (2021) (cyan). The regional VS model derived from ambient noise tomography is shown in the background, while the black lines indicate the Moho of the overriding Myanmar plate (Wu et al., 2021). The red line indicates the top of the subducting Indian slab from slab2, whereas the dashed black lines approximate the ∼30 km thickness of the continental crust proposed by Zheng et al. (2020), Bai et al. (2021), and Zhang, He, et al. (2021). The blue and red dashed boxes in profile C–C′ represent the high-angle thrust earthquakes in the lower crust to uppermost mantle beneath the eastern IMR and the thrust earthquakes within the lower crust of the subducting Indian plate, respectively. Elevation profiles (SRTM90m) are plotted at the top of each panel.

    • These are the cross sections with the mechanisms plotted along the Saigang fault.
    • The M 7.7 earthquake slipped much of (if not all) of the Meiktila section of the Sagaing fault..


      • (a) Focal mechanisms of M >4 earthquakes in our catalog colored by centroid depth and Global CMT mechanisms (1976–2021; gray). The circles represent relocated seismicity from ISC-EHB catalog (1964–2018; gray), Zhang, He, et al. (2021) (2016–2018; cyan) and Mon et al. (2020) (2016–2018; magenta). The colored lines represent estimated locations of Global Positioning System (GPS) transects from Maurin et al. (2010) (purple, MR1-3) and Tin et al. (2022) (magenta, TH1-3). The white squares indicate major cities close to the SF. (b) Earthquakes from our catalog located within 10 km of the Sagaing fault are projected along the profile A–A′. A larger projection width is used for Global CMT (40 km) due to its larger centroid location uncertainty. The VS model from Wu et al. (2021) is plotted in the background. The locking depth of different segments of the fault from GPS transects are plotted as vertical arrows, and the estimated slip rates in mm/ yr are indicated. The elevation (SRTM90m) along the profile is shown at the top. The white inverted triangles show the location of the profile segments in panel (a).

    • Here is a different cross section that shows how Maurin and Rangin (2009) interpret this plate boundary to have an oblique sense of motion (it is a subduction zone with some strike slip motion). Typically, these different senses of motion would be partitioned into different fault systems (read about forearc sliver faults, like the Sumatra fault. I mention this in my report about the earthquakes in the Andaman Sea from 2015.07.02). This cross section is further to the south than the one on the interpretation map above. I include their figure caption as a blockquote below.


      • Present cross section based on industrial multichannel seismics and field observations. The seismicity from USGS catalog and Engdahl [2002] is represented as black dots. Focal mechanisms from Global CMT (http://www.globalcmt.org/CMTsearch.html) catalog are also represented.

    • This figure shows the interpretation from Maurin and Rangin (2009) about how the margin has evolved over the past 10 Ma.


      • Cartoon showing the tectonic evolution of the Indo-Burmese Wedge from late Miocene to present.

    • Wang et al. (2014) also have a very detailed map showing historic earthquakes along the major fault systems in this region. They also interpret the plate boundary into different sections, with different ratios of convergence:shear. I include their figure caption as a blockquote below.


      • Simplified neotectonic map of the Myanmar region. Black lines encompass the six neotectonic domains that we have defined. Green and Yellow dots show epicenters of the major twentieth century earthquakes (source: Engdahl and Villasenor [2002]). Green and yellow beach balls are focal mechanisms of significant modern earthquakes (source: GCMT database since 1976). Pink arrows show the relative plate motion between the Indian and Burma plates modified from several plate motion models [Kreemer et al., 2003a; Socquet et al., 2006; DeMets et al., 2010]. The major faults west of the eastern Himalayan syntax are adapted from Leloup et al. [1995] and Tapponnier et al. [2001]. Yellow triangle shows the uncertainty of Indian-Burma plate-motion direction.

    • Here is the map showing the SF fault segments (Wang et al., 2014).


      • Fault segments and historical earthquakes along the central and southern parts of the Sagaing fault. Green dots show relocated epicenters from Hurukawa and Phyo Maung Maung [2011]. Dashed and solid gray boxes surround segments of the fault that ruptured in historical events. NTf = Nanting fault; Lf = Lashio fault; KMf = Kyaukme fault; PYf = Pingdaya fault; TGf = Taunggyi fault.

    • Here is a Sloan et al. (2017) map that shows fault plane solutions (including the 1930 M 7.3 SF earthquake) for earthquakes in the region.


      • Seismotectonic map of Myanmar (Burma). Faults are from Taylor & Yin (2009) with minor additions and adjustments. GPS vectors show velocities relative to a fixed Eurasia from Maurin et al. (2010). Slip rate estimates on the Sagaing Fault are given in blue and are from a, Bertrand et al. (1998); b, Vigny et al. (2003); c, Maurin et al. (2010); and d, Wang et al. (2011). Major earthquakes (Ms ≥7) are shown by yellow stars for the period 1900–76 from International Seismological Centre (2011) and by red stars for the period 1836–1900 from Le Dain et al. (1984). The location and magnitude of theMb 7.5 1946 earthquake is taken from Hurukawa&Maung Maung (2011). Earthquake focal mechanisms are taken from the GCMT catalogue (Ekström et al. 2005) and show Mw ≥5.5 earthquakes, listed as being shallower than 30 km in the period 1976–2014. IR, Irrawaddy River; CR, Chindwin River; HV, Hukawng Valley; UKS, Upper Kachin State; SF, Sagaing Fault; KF, Koma Fault. The inset panel is an enlargement of the area within the dashed grey box. It shows the dense GPS network in this area.

    • This map shows that the region where the 28 March 2025 M 7.7 earthquake is located is in the region of uplifted regions along the SF (Sloan et al., 2017).


      • Regional setting, and fault geometries and uplift distribution associated with the Sagaing Fault.

    • Here is a comprehensive map showing the complicated tectonics of this region (Sloan et al., 2017).


      • Regional tectonic setting of the Andaman Sea Region modified from Morley (2017). See text for explanation of labels A–E. The locations of Figures 2.15– 2.17 are indicated.

    • This map shows how Rangin (2017) hypothesizes about the platelets formed along the plate boundary.


      • Extension of the Burma–Andaman–Sumatra microplate (shown in green). The Burma Platelet is the northern part in Myanmar. Active faults are shown in red and inactive faults in purple. The post-Santonian magnetic anomalies and associated transform faults of the Indian and Australian plates are suggested in blue. Left-lateral red arrows along the 90° E Ridge illustrate left-lateral motion between the Indian and Australian plates. India/Eurasia relative motion is shown with a yellow arrow, India/Sunda motion with purple arrows and Australia/Sunda motion with black arrows (modified from Rangin 2016).

    • This is a great summary figure from Ranging (2017) showing how these plates and platelets interact in this region.


      • Structural map of the active buckling of the Burma Platelet considered not to be rigid. The curved Sagaing Fault, Lelong, Kaladan and coastal faults outline this arched platelet. WSW extrusion of the platelet is outlined by the NE–SW diffuse dextral shear south of the South Assam Shear Zone into the north and by the left lateral Pyay-Prome shear zone in the south. The western margin (CSM: collapsing Sunda margin) of this platelet is affected by dextral wrench and active collapse of the continental margin, but no sign of active subduction was found. This platelet is bracketed tectonically between the drifted 90° E Ridge and the accreted volcanic ridges into the south and the Eurasian Buttress (Himalayas and Shillong) into the north. The East Himalaya Crustal Flow (EHCF; large curved red arrow) imaged in the East Himalaya Syntaxis (EHS) is induced by the Tibet Plateau collapse and could be an important component of the tectonic force causing the platelet buckling. The Burma Platelet is jammed between the Accreted Volcanic Ridges in the south, and the Shillong Plateau crustal block in the north, participate to the buckling of the Myanmar Platelet. BBacc, Bay of Bengal attenuated continental crust (Rangin & Sibuet 2017); CMB, Central Myanmar Basins; CMF, Churachandpur-Mao Fault (Gahalaut et al. 2013).

Geodetic Analyses

  • Geodesy is the study of the motion of the Earth. The data used to measure how the Earth moves can be from GPS data, tide gage data, benchmark surveys, and satellite remote sensing data (e.g. InSAR, LiDAR, etc.). The motion can be partitioned into different directions (e.g. horizontal, vertical, and rotational).
  • The maps below are from Taylor and Yin (2009, lower map) and Zhang et al. (2004, upper map) shows the velocity (speed) of locations where GPS locations (positions) have been collected over a period of time (probably decades). The arrows called vectors represent the direction of motion and the rate of motion (speed or velocity). The GPS sites are where the dots are and the uncertainty (sometimes called error) of the velocity calculation is represented by the ellipse at the tip of the arrow.
  • These arrows represent motion relative to stable Eurasia. So, arrows that are pointing to the north tell us that that GPS site is moving north relative to Eurasia. Unfortunately there is no scale, but based on the Zhang et al. (2004) paper (also shown below), the most southwest GPS site (in India) has a velocity of about 25 mm per year (mm/yr)
  • We can make some simple observations and interpretations from these data. Look at the lower map with the red and blue arrows (vectors).
    1. GPS sites in northern India (in the lower left (southwest) part of the map) show that this region is moving north-northeast relative to Eurasia. This matches the long term motion of the India plate we discussed in the introduction to this report above.
    2. GPS sites in the Tian Basin (the low, green colored area in the central upper left (northwest) part of the map) are also moving north relative to Asia. However, they are moving to the north more slowly than the sites in India
    3. Because the GPS sites (and the crust in that location) are moving slower in the north, north of the Himalaya and Tibetan Plateau. This tells us that the crust is slowing down between India and the Tarim Basin. Why is this?
    4. The crust is slowing down because the crust is deforming, either elastically where the deformation of the crust buldges up or flexes sideways, or anelastically where the deformation is accommodated by fault slip on tectonic compressional faults (e.g. reverse or thrust faults).
    5. Note how these GPS plate motion vectors (the red and blue arrows) change whether they are slightly to the east or slightly to the west of North. In northeast India, the motion is slightly to the northeast and in the Tarim Basin some of them are moving slightly to the west. If this difference is larger than the error ellipses, it would tell us that the crust may also be experiencing changes in lateral motion through this region. This type of lateral motion may be accommodated by strike-slip faults (see the arrow shaped figure from Taylor and Yin (2009) below).


  • Caption from Zhang et al., 2004)

    • Global positioning system (GPS) velocities (mm/yr) in and around Tibetan Plateau with respect to stable Eurasia, plotted on shaded relief map using oblique Mercator projection. Ellipses denote 1s errors. Blue polygons show locations of GPS velocity profiles in Figures 3 and DR1 (see footnote 1). Dashed yellow polygons show regions that we used to calculate dilatational strain rates. Yellow numbers 1–7 represent regions of Himalaya, Altyn Tagh, Qilian Shan, Qaidam Basin, Longmen Shan, Tibet, and Sichuan and Yunnan, respectively.

  • Caption from Taylor and Yin (2009), Figure 4 is the arrow shaped figure below.

    • Color-shaded relief map of the Indo-Asian collision zone with global positioning system (GPS) velocities (arrows) from the Zhang et al. (2004) compilation. Blue arrows indicate data used in Figure 4A and line indicates data used in Figure 4B.

  • Here is the Sloan et al. (2017) map showing the faults and GPS derived plate motion.


    • Seismotectonic map of Myanmar (Burma) and surroundings. Faults are from Taylor & Yin (2009) with minor additions and adjustments. GPS vectors show velocities relative to a fixed India from Vernant et al. (2014), Gahalaut et al. (2013), Maurin et al. (2010) and Gan et al. (2007). Coloured circles indicateMw > 5 earthquakes from the EHB catalogue. Grey events are listed for depths <50 km, yellow for depths of 50–100 km and red for depths >100 km. The band of yellow and red earthquakes beneath the Indo-Burman Ranges represents the Burma Seismic Zone. The dashed black line shows the line of the cross-section in Figure 2.13. ASRR, Ailao Shan–Red River Shear Zone.

  • Here is a geodetic analysis for the slip rate of the Sagaing fault from Wigny et al., 2003.
  • First we see the map showing the east-west profile.


    • (top) Regional and Myanmar velocities in the Sundaland reference frame. (bottom) Mandalay area transect stations. Error ellipses show the 99% confidence level of formal uncertainties given in Table 1.

  • In the plot we see geodetic velocities (how fast different benchmarks are moving) relative to each other.
  • On the west side of the fault the benchmarks are moving relatively northwards and on the east side, the benchmarks are moving relatively south.
  • The difference between the rates on the west and the rates on the east tells us how much slip the fault is accumulating per year.
  • These authors estimate that the Sagaing fault is accumulating 18 mm/yr of slip. This rate is called the slip rate or slip rate deficit.


    • Elastic loading across Sagaing fault. Fault parallel velocity component in mm/yr (dots) as a function of distance to fault trace. Gray, solid, and open circles represent northern, central, and southern transect fault parallel velocities, respectively. The solid curved line shows the best fit profile obtained for a locking depth of 15 km. Vertical dashed line shows location of the Sagaing fault, 17 km west of the elastic dislocation.

  • Here are some fault slip rate estimates from Tun and Watkinson (2017). The three profiles are oriented east-west across the fault
  • In each plot on the right, we see geodetic velocities (how fast different benchmarks are moving) relative to each other.
  • Slip rates (i.e., slip rate deficits”) for these profiles, from north to south, are 21.1, 21.1, and 22.4 mm/yr.
  • Profile 3 is located closest to the M 7.7 earthquake.


    • GPS vectors from all published surveys within Myanmar and around the eastern Himalayan syntaxis. After Maurin et al. (2010). Stations referred to in the text are marked as yellow triangles.

  • Here are some results from Tin et al. (2022).
  • Tin et al. (2022) use geodetic data to evaluate the slip rates along the Sagaing fault system.
  • They model different rates along each segment and the sigmoidal lines in the plots on the right represent the different models and how they fit these data.
  • From top to bottom, the slip rate is estimated to be 22.8, 23.7, and 15.8 mm/yr.


Earthquake History

    • This map shows the earthquake history along the Sagaing fault (Hurukawa & Maung, 2011).


      • Epicentral distribution of 18 earthquakes analyzed in this study. (a) Epicenter locations according to ISS (International Seismological Summary) and ISC (International Seismological Centre) data. (b) Locations of epicenters relocated by the MJHD (Modified Joint Hypocenter Determination) method in this study. Red and blue circles indicate earthquakes before and after 1964. The numbers assigned to each earthquake indicate the year and month of M≥ 7.0 earthquakes and of the January 1991 earthquake. Numbers 1 and 2 (not in parentheses) indicate foreshocks of the December 1930 earthquake; number 3 indicates an aftershock of the January 1931 earthquake. Because two earthquakes occurred in September 1946, their sequence is indicated by numbers in parentheses. Large, intermediate, and small open circles indicate earthquakes with M ≥ 7.0, M ≥ 6.0, and unknown magnitude, respectively. Red lines in Figure 2b show the fault planes of the M ≥ 7.0 earthquakes analyzed in this study. Solid arrows indicate the rupture directions of the M ≥ 7.0 earthquakes. The paired arrows in Figure 2a indicate the sense of movement along the Sagaing Fault. Dotted arrows in Figure 2b indicate seismic gaps. The green star denotes Nay Pyi Taw, a new capital of Myanmar.

    • Here is another earthquake history map (methinks this is from Wang as it matches maps in Wang et al., 2014).
    • This is the same inset in the main interpretive poster.


    • The upper panel is a map that shows the fault systems (Wang et al., 2014).
    • The center panel shows fault sections and proposed earthquake magnitudes that each section may host.
    • The lower panel is a space-time diagram showing historic earthquakes. Time is on the vertical axis and space is on the horizontal axis (aligned to the map)


      • Map and chart of potential maximum earthquake magnitudes (Mw) associated with named segments of the Sagaing fault. Blue arrows show the boundaries of fault segments. Ruptures of the past century appear in the lower box. Green lines are the proposed rupture patches along the Sagaing fault since the beginning of the twentieth century; gray line shows the proposed rupture section along the Kyaukkyan fault, parallel to the Sagaing fault. Red linemarks the possible rupture patch of the 1839 earthquake, inferred from historical data. BMs = Ban Mauk segment; TMs = Tawma segment; IDs =In Daw segment; MIs =Mawlu segment; SZs =Shaduzup segment; KMs = Kamaing segment; MGs =Mogang segment.

    • When an earthquake fault slips, it squishes the surrounding lithosphere or mantle. This changes the stress on faults within this deforming lithosphere or crust.
    • In some places the stresses on faults increase and in other places the stresses decrease.
    • One can use earthquake histories to evaluate the changes in static coulomb stress along adjacent faults.
    • Xiong et al. (2017) use these earthquakes to study the accumulation or release of stress over time to consider whether a fault may be loaded towards earthquake rupture.
    • Here is a map showing the earthquakes used in their study.


      • Map shows location of the SF region and 10 earthquakes (M > 6.5) along the fault from 1906 to 2003. The open red circles and beach balls display the proposed [Maurin et al., 2010; Kundu and Gahalaut, 2012; Hurukawa and Maung Maung, 2011] and the modified epicenters in this study, respectively. The black beach balls indicate the large historical earthquakes. The black solid lines and black thick lines represent faults and ruptured segments, respectively. The grey lines are other active faults in this region. The red dashed line indicates the unruptured section on Sunda Trench. The green stars denote the cities with population more than 1 million. Shaduzup (SZs), Kamaing (KMs), and Mogang (MGs) segments are three strands on the northern Sagaing fault system [Wang, 2013]. Nay Pai Taw is the new capital of Myanmar, and Yangon is the largest and highest populated city of Myanmar. Inset shows study area at regional scale. The segments are labeled right of the figure, after Wang [2013].

    • This map shows the changes in coulomb stress over time.


      • (a–i) ΔCFS evolution since 1906. The black thick line indicates the SF. The thick green, red, and gray lines represent the portion of the next earthquake rupture, the current earthquake rupture, and the previous ruptured portions, respectively. Figures 2a–2i indicate the ΔCFS immediately before the earthquake labeled by green thick lines; the label of year in each figure indicates the occurrence time of event labeled by red thick line.

    • This map shows change in coulomb stress for specific times.


      • (a) ΔCFS (coseismic and postseismic) on the SF in the year of 2016. Units A–C are the three sections on which ΔCFS is significantly positive. (b) Stress accumulation on the SF caused by the tectonic loading of 10 years. (c) Time for tectonic loading being equivalent to the ΔCFS in Figure 3a. In this study, time for tectonic loading is calculated by dividing the earthquake-induced ΔCFS with the tectonic loading rate.

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    References:

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    • Specific References

  • Curray, J.R., 2005. Tectonics and history of the Andaman Sea Region in Journal of Asian Earth Sciences, v. 25, p. 187-232.
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